ELECTROPLATING AT HOME - WorldRadioHistory.Com...were a modern invention. The fact is that from the earliest days of the cinema-tograph there have been literally dozens of inventions

ELECTROPLATING AT HOME

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May, 1953 NEWNES PRACTICAL MECHANICS 317

M AY,1953

VOL. XXNo. 233

PRACTICALMECHANICS

EDITOR

F. J. CAMM

Owing to the paper shortage "The Cyclist," "Practical Motorist," and "Home Movies " are temporarily incorporated.

By The Editor

3-D DEVELOPMENTSSTEREOSCOPIC films have been

much discussed in recent weeksin newspapers as though they

were a modern invention. The fact isthat from the earliest days of the cinema-tograph there have been literally dozensof inventions for three-dimensionalfilms. In almost every case the vieweris expected to wear special glasses, andthe three-dimensional films being shownto -day, with two exceptions, still makeuse of that system, which has manydefects, not the least of which is that ifone's eyes are not perfectly matched, orif there is myopia or astigmatism in oneof them, the picture is not seen in threedimensions but becomes blurred.

Although colour films have mademarked progress in the last twenty yearsthey are still far from perfect. No onehas produced a film in natural colours ;they all look lurid and unreal. Thesame applies to colour photography.

With television the projection ofpictures in colour has made some pro-gress-no more than that. Such de-monstrations as I have witnessed, in-cluding a demonstration by the lateBaird and another by a well-knowntelevision manufacturer, merely indicatethat colour television is possible at somedistant date.

PROJECTION TVUNTIL someone can discover a means

of amplifying light as we can nowamplify sound, the development ofprojection TV will be hampered, becauseas the picture is " blown up " the lightdiminishes and the picture takes on awoolly aspect. This is not particularlynoticeable with pictures up to, say,loin. square, but for big screen tele-vision the problem becomes more diffi-cult of solution. It is my view, however,that eventually all TV receivers willmake use of a tiny tube which ischeaply replaced, in conjunction withan optical system incorporating theBresnel lens.

3-D television is already on the wayand is being considered by the BBC.Viewers will not need special glasses,merely a simple attachment to theviewing screen. This system can easilybe adapted for the cinema showing of

Fair Commentfilms and would require only mildalteration to existing apparatus.

Great strides are being made almostevery month in the science of television,one of the latest being automatic picturecontrol, which was recently demon-strated in London.

In many TV areas to -day a certainamount of signal fading occurs. Someplaces are far worse than others, but inmany districts, at some time during anevening's entertainment, controls haveto be reset due to a change in signalstrength. It is claimed that automaticpicture control TV will provide asteady picture of constant contrast andbrilliance even though signal strengthvaries by as much as z0 to i.

This was proved convincingly at thedemonstration, and although the pictureblacked out completely on an ordinaryTV receiver due to signal fading, theautomatic picture control set was notnoticeably affected.

A further advantage with this new setis the " interference damper," a devicewhich makes for a considerable reduc-tion of " snowstorm " interference. Inthe bright areas of the picture streaks ofinterference stay white, but in darkareas where they have shown up whitebefore on the screen they now becomegrey and are practically invisible.

TV AS AN AID TO INDUSTRYA RECENT application of TV is as

an aid to industry and science inobservation techniques, and the threecompanies manufacturing TV camerasare all producing apparatus for this

SUBSCRIPTION RATESincluding postage for one year

Inland - - - - 14s. per annum.Abroad - - - - 14s. per annum.Canada - - 13s. per annum.Editorial and Advertisement Office : " Practical

Mechanics," George Newnes, Ltd.,Tower House, Southampton Street, Strand, W.C.2

'Phone : Temple Bar 4363Telegrrns : Newnes, Rand, London.

Registered at the G.P.O. for transmission byCanadian Magazine Post.

Copyright in all drawings, photographs andarticles published in "Practical Mechanics " isspecially reserved throughout the countriessignatory to the Berne Convention and theU.S.A. Reproductions or imitations of any of

these are therefore expressly forbidden.

purpose. Cameras have graduallyacquired more lenses and up to six arenow accommodated on the lens turret,providing a wide and flexible range ofviewing angles. Dangerous research canbe made more safe by the use of suitablysited cameras. Electrically, experimentsconnected with circuit breakers operatingat high voltages are too dangerous foranyone to approach nearer than 2ooft.,whereas a camera can be placed intoposition only 3ft. from the main rotorof a 40o kV generator, providing theengineers with a close-up of whathappens when a generator is shortcircuited through tests.

Remote control of a large crane byradio and TV permits the crane to handledangerous products such as atomicmaterial in bulk, and the operator cansee what the crane is doing withoutexposing himself to danger.

DEVELOPMENTS IN SAFETYAT SEA

ANEW device for saving lives at seawas recently demonstrated in Lon-

don. It consists of a transmitter fittedinto a small box no larger than 12in. x7in. x Sin. deep, bolted to the undersideof the thwarts or seats of a lifeboat.

The only action that the unfortunatesin the boat have to take is to mount therod type aerial by a simple plug-inaction and then turn the handle of thetransmitter until a small neon light comeson and continue turning the handle untilthe signal is seen to be going out. Thisis shown by means of another neon in-dicator which blinks according to themorse signal being radiated.

Part of the signal is a continuous toneand rescuing ships can use it for directionfinding and navigating on to thoseadrift.

It is true that, by regulation, wirelesstransmitters have to be fitted in a pro-portion of the ship's lifeboats, andalthough it may be possible in a largenumber of cases to find the lifeboat withthe transmitter, it is virtually impossible,in anything like a heavy sea, for a flockof lifeboats not so equipped to keepwithin hail of the transmitting boat.

It is with the object of equippingthese other boats that this transmitterhas been developed.-F. J. C.


318 NEWNES PRACTICAL MECHANICS May, 1953

. .

LITCY OTLEFE gATEEThe Theory of Electroplating and its Practica Application in the Home Workshop

ELECTROPLATING is the process ofdepositing on a base metal a thin,

uniform, adherent, non -porous coatingof some other metal, from a solution of asuitable salt of this metal, by the use of anelectric current.

Reasons for ElectroplatingThere are many reasons why such a coat-

ing may be advantageous. For reasons ofmechanical strength and ease of working, thetwo metals most commonly used in engineer-ing are iron (including steel) and brass. Bothiron and brass are subject to attack by gasesof the atmosphere. In the case of iron, rust-ing with consequent loss of strength occurs,while in the case of brass, tarnishing spoilsthe appearance of the article. Electroplatingboth iron and brass with a coating of somesuitable metal, such as nickel or chromium,prevents the process of tarnishing and at thesame time provides a surface of permanentand attractive lustre. In the case of carlamp reflectors, the coating serves anotherpurpose. The reflector is easily spun frombrass, but brass tarnishes rapidly and wouldrequire constant polishing, and, added to this,brass has a yellow colour. Coloured objectspossess their colour by virtue of the fact thatthey absorb and abstract certain wavelengthsfrom white light ; thus coloured objects donot reflect all the light which falls upon them.By coating brass with a " white " metal, ahigher proportion of the light is reflected andthe reflector is thus made more efficient. Themetals commonly used for plating reflectorsare chromium and silver. Whether electro-plating beautifies an object is a controversialsubject with which I am not going to dealhere ; some readers may hold one opinion andothers another. There is one charge, how-ever, that cannot be laid against electroplating,and that is that it covers slip -shod work. Ifanything, the very reverse is true, for theeffect of plating a roughly finished article isto bring out all its deficiencies. More willbe said about this later when the practicalaspect of the subject is dealt with. Beside theadvantages mentioned above, there are otherspecialised uses for electroplating which neednot concern us here.

Theory of ElectroplatingIn order to understand the theory of

electroplating, it is necessary to know a littleabout the atomic structure of the elements.The full theory of this structure is, of course,a complicated affair, and so, in the followingparagraphs, I have attempted to develop asimplified version which covers just theground that we require.

Atomic StructureEvery material thing in this world, indeed in

the whole universe, is built up of an enormousnumber of minute particles which we callatoms. The atoms themselves are built upof three types of extremely small particles.These particles are known as protons, neu-trons and electrons. The proton is a rela-tively large particle which possesses a unitpositive electric charge. (The significantword here, is " relatively," since the actualmass of a proton is approximatelyo.00000000000000000000000t7 grams.There are about 28 grams in one ounce.)The neutron is a particle which is ofapproximately the same mass as a proton butwhiet possesses no electrical charge. The

By E. HARRIS MORGAN, B.Sc.

electron is an extremely minute particle(about t/t800th of the mass of a proton)possessing unit negative electric charge.

Now the atom is electrically neutral andtherefore must contain an equal number ofunit positive and unit negative charges, or,to put it another way, an equal number ofprotons and electrons. The positive charges,

0- ELECTRON

0 PROTON (P)

() NEUTRON (N)

O

Hydrogen

NucleusOrbit

Helium

Lithium Beryllium Boron

Fig. 1.-Diagrams illustrating the structureof the atoms of a few of the elements.

or protons, are clustered together in thecentre of the atom together with a certainnumber of neutrons, and this cluster is knownas the nucleus. Around the nucleus revolvea number of electrons equal to the numberof protons in the nucleus. These electronsrevolve in well defined paths, or orbits, aboutwhich more will be said later.

The simplest atom is one which has one

proton and one electron. This is the atomof hydrogen. In Fig. t there are shownthe atoms which result by taking first one,then two, then three protons, and soon. Itwill be noticed that in the nucleus of all theatoms, except that of hydrogen, there appear anumber of neutrons. It so happens, that inthe atoms illustrated in Fig. t, the number ofneutrons is the same as the number of protonsbut this is not necessarily always the case. Inthe case of the element lithium, it will be seenthat the extra electron takes up a new path,and that we now have two orbits. Eachadditional electron enters the second orbituntil there are eight electrons in this orbit,and then a third orbit is started. It is aninteresting fact that the elements with eightelectrons (or an octet) in their outermost orbitare all chemically inert ; that is to say, theydo not join with other elements to form com-pounds.

ElectrolytesThere are two main classes of compounds,

electrolytes and non -electrolytes. It is theelectrolytes with which we are concerned inelectroplating, and the theory which followsis confined to this class of compound.

The atoms of active elements, in combiningto form compounds, either give or receiveelectrons so that the outermost orbit possessesa complete octet. In Fig. 2a the atoms ofpotassium and chlorine are shown diagram-matically. It will be noticed that thepotassium atom has one electron in its outer-most orbit, and the atom of chlorine has sevenelectrons in its outermost orbit. Whenpotassium and chlorine combine to formpotassium chloride, each potassium atomgives one electron to each atom of chlorine,as shown in Fig. 2b. Each potassium atom

Young soldiers receiving instruction in electroplating at the Army Technical School, Arbarfie d,Berks.



is now left with a complete octet and eachchlorine atom also possesses a complete octet.There is a very important outcome to thischange however. If the charges at the centre(the protons), and the charges in the orbits(the electrons), are balanced, it is found thatthe potassium atom now has an extra unitpositive charge, and the chlorine atom anextra unit negative charge. Thus, potassiumin potassium chloride is not in the form ofa potassium atom but in the form of a posi-tively charged atom, and the chlorine in theform of a negatively charged atom. Thesecharged atoms are known as ions, and havevery different properties from unchargedatoms. A positively charged atom is knownas an anion, and a negatively charged atomis known as a cation. Since the ions ofpotassium and chlorine are present in equalquantities in potassium chloride, thesecharges cancel each other, and the net resultis that potassium chloride has no charge.

The above theory can be applied to anyelectrolyte, and it therefore follows that anyelectrolyte can be divided into two sets ofparticles, anions carrying a positive chargeand cations carrying a negative charge.

Electrolytes in SolutionWhen an electrolyte is dissolved in water

it breaks up (or ionises) into its constituentions (to a greater or lesser degree). Sincethese ions carry electric charges they arecapable of carrying an electric current.Thus, solutions of electrolytes are conductorsof electricity.

It is now necessary to consider the natureof an electric current. An electric currentmay be regarded as a flow of electronsthrough a wire or other conductor. Abattery or generator can be considered to bea pump which promotes this flow. Thedirection of the flow is from the negativepole of the battery, through the circuit andthen back to the positive pole. (This is inthe opposite direction from the conventionaldirection of flow of an electric current, i.e.,from positive to negative. This -is becausethe convention was decided upon before thetrue nature of electricity had been estab-lished.) Fig. 3a is a diagram showing theflow of electrons through a circuit. If wereplace the resistance of Fig. 3a by a vesselcontaining an electrolyte, leading the currentinto and out of the electrolyte by means ofmetal plates, we get the arrangement shownin Fig. 3b. The metal plates which areused to introduce the current into the electro-lyte are known as electrodes. The electrodeconnected to the negative pole of the battery

Potassium atom

©Potassium ion

Chlorine atom

Chlorine ion

Fig. 2.-(a) Diagrammatic representation ofatoms of potassium and chlorine. (b) Ions ofpotassium and chlorine formed by the transferof an electron from the potassium atom to thechlorine atom. (Note that the ions have eight

electrons in their outermost orbits.)

is called the cathode, and that connected tothe positive pole is called the anode.

I have shown that the solution of anelectrolyte contains charged particles, theions. The effect of passing an electriccurrent through an electrolyte is to causethe electro-positive ions or anions to movetowards the cathode where they receive anelectron, so converting the ion back into afree atom. The cations, on the other hand,move towards the anode where they are dis-charged and converted into atoms, their spareelectrons being absorbed into the circuit.

O

Electron flow

Resistance

1

NC- ArcElectron flow

Anode Cathode

Fig. 3.-(a) Electron flow in a simple circuit.(b) Electron flow through an electrolyte.

It is thus possible to deposit the electro-positive or metallic part of the compoundon the cathode, the electro-negative partbeing deposited on the anode. By a suitablechoice of electrolyte, and by using the samemetal- for the anode as is present in thecompound, it is possible to ensure that theelement or group set free at the anode attacksthe anode and dissolves it in the form of ions.Thus the strength of the solution is main-tained and metal is effectively transferredfrom the anode to the cathode. This is theprinciple of electroplating, although forpractical reasons certain departures are madefrom the simple theory outlined above.

Copper wires

Fixed electrode(Copper)

MoveableelectrodeCopper)

Electrodedetail

Copper sulphatesolution

(4oz/prnt)

Stone jar

Fig. 4.-Circuit resistance. Variation of theresistance is obtained by altering the positionof the movable electrode. Some simple arrange-ment for maintaining the electrode at the

required height should be adopted.

Factors Governing the Nature of theDepositTo be effective the deposit of the metal

used for plating must possess certairproperties. It must first be uniform. Thiscondition is obtained by placing the articleto be plated as a cathode between twcanodes, or, in certain cases, by makingarrangements for the rotation of the articleduring the plating operation. Secondly, thedeposit must have good adhesion with thearticle being plated. In order to obtain thiscondition all surfaces to be plated must bescrupulously clean and free from grease.Details of the process involved in cleaningand preparing for plating will be given later.The third desirable property is a depositwhich is already in a highly polished condi-tion, or one which can be worked up to ahigh polish. This last property is one whichis most difficult to obtain, as the nature ofthe deposit depends on a number of factors.The solutions used are not merely solutionsof simple salts, but are solutions to whichother chemicals, which play an importantpart in the process, have been added. Thetemperature of the plating solution is alsoof importance, different types of deposit beingproduced by solutions at different tempera-tures. Another important factor is thecurrent density. This is the current flowingper square inch of surface area of thecathode. Beside these factors, others, suchas the ratio of anode area to cathode areaand the strength of the solution, play theirparts. A good deal of research has beenmade on these factors enumerated above, andthe result has been a series of formula andtechnical details- which makes successfulelectroplating a practical possibility.

Apparatus RequiredThe apparatus required to electroplate

successfully in the home workshop dependson the size of the article to be plated. Ingeneral, the larger the article, the more com-plicated and expensive becomes the apparatusneeded. For small articles, such as the modelengineer might require to electroplate, theapparatus can be reasonably inexpensiveand uncomplicated.

Plating VatA glass beaker, such as is used in a

chemistry laboratory, makes a most con-venient plating vat for small articles. Thesebeakers can be obtained in a variety of sizesfrom any laboratory suppliers or chemistsand are not expensive. Since the platingsolutions are used hot, a beaker made of heat-resisting glass should be chosen.

ThermometerA thermometer which has the scale

engraved on the stem is necessary. Thereare many types to choose from and oneshould be selected which can be read easily.Two temperature scales are in current use,the centigrade and the Fahrenheit, and forthis reason temperatures will be given onboth scales. The thermometers should readfrom o deg. C. -s so deg. C. in the case of thecentigrade scale, and from o deg. F.-250 deg. F. in the case of the Fahrenheitscale.

Electrical InstrumentsSuitable instruments can be purchased

from advertisers in this journal. Two instru-ments are normally used, a voltmeter andan ammeter. Of these the ammeter is themost important, and, indeed, for simple workthe voltmeter is not essential. The amateuris advised to dispense with the voltmeter.The ammeter range depends on the type ofplating and the surface area to be plated.For most small work an ammeter reading



up to 5 or to amps is suitable, but if largeareas are to be plated, instruments readingup to 3o amps may be necessary. It ispossible to purchase an instrument which canbe converted to the required scale by addingsimple resistances as shunts.

Circuit. ResistanceThe circuit resistance is capable of varia-

tion, so that the current flowing in thecircuit can be controlled. The resistanceshould be variable between about o and15 ohms, and should be capable of carryingthe maximum current to be used. Ready-made sliding resistances are available, butthey are expensive, and the reader is advisedto construct one as shown in Fig. 4.

Power SuppliesFor small work, an ordinary six -volt dry

battery gives quite satisfactory results, but itis preferable to use a bank of three accumu-lators, which have the advantages of beingable to deliver a much greater current and ofbeing recharged. A six- or 2 -volt carbattery, if available, is admirably suited forthe operation.

"""---- Switch

Voltmeter(may be omitted)

Article beingplated

thin, has very little effect on the appearanceof the finished article, but when we come toplate the article, the grease, being a non-conductor, will prevent the flow of electricityat various points and thus prevent the forma-tion of an even coating of the plating metal.Moreover, when plating does occur, there willbe poor adhesion with subsequent peelingof the plating. An oxide layer will producethe same effects, and it is important toensure that once the article has been pre-pared it is plated without delay.

DegreasingIn order to degrease the article, it should

be immersed in a hot solution of causticsoda for about five minutes. The causticsoda solution can be prepared by dissolvingtwo ounces of caustic soda in one pint ofwater. A glass vessel should be used asa container for the solution. The articleis then rinsed in clean water and immersedin a dilute acid. Sulphuric acid is used forthe treatment of iron and steel articles, andnitric acid for articles of copper and brass.The dilute sulphuric acid is made up bydiluting one ounce of concentrated sulphuric

k6 Volt- batteryCircuit

resistance

Anode

Fig. 5.-Diagram of the Anode

circuit to be set up forplating.

SwitchSome simple switching arrangement, capa-

ble of making and breaking the circuit at theparticular current value used, is necessary.When the current is below 5 amps, a knifeswitch of simple design is satisfactory, butfor higher current values a switch designedto make and break at that value should beused. (Of course, there is no objection tousing a switch designed for 3o amps tobreak a circuit carrying 2 amps.) A low -voltage switch of the required type- can beobtained from a dealer in car accessories.

ChemicalsThe various chemicals used in the pro-

cesses will be detailed under the appropriateheadings.

Other ApparatusA quantity of connecting wire (copper 16

gauge) and a few crocodile clips are neces-sary for setting up the circuits. A pintmeasure will also be required for making upthe solutions.

Preparing the Article for PlatingThe golden rule of electroplating is that

the quality of the plating can never be betterthan the surface finish of the article beingplated. Every care should be taken, there-fore, to obtain as fine a finish as possible.All tool marks must be removed by thejudicious use of emery paper or a buffingwheel.

During its manufacture, the article willinevitably have picked up an uneven layer ofgrease. This layer, being normally quite

Platingvat Note : The plating solution

is brought to the requiredtemperature before switch-

ing on the current.

acid with three pints of water, and the nitricacid by diluting four ounces of con-centrated nitric acid with three pints of water.(WARNING. It is important to note thatthe acid must be added to the water, andnot the water to the acid. Stir well whencarrying out the addition.) The time ofimmersion should be between one and twominutes. A further rinse in clean waterfollows, and the article is then given a finalpolish with a damp cloth charged withpumice powder. After these operations thearticle is given a thorough wash in runningwater and transferred immediately to theplating bath. It should not be dried betweendegreasing and plating.

During the degreasing operation, thearticle should not be touched by the fingers.It is an easy matter to bend up a simplepair of tongs from wire or strip, and theseshould be used to handle it.Setting Up the Apparatus

The apparatus is set up as shown inFig. 5 (the voltmeter being omitted if notavailable). The vat is filled with the plat-ing solution at a temperature a few degreesabove that given (in order to allow for cool-ing during the operation). The solution canbe heated by placing the vat in a saucepanof water over a fire. A more convenientarrangement is to heat the vat directly, bystanding it on a wire gauze placed on atripod, and heating with a bunsen burner.In this way, a greater control over thetemperature of the solution is obtainable.Method of Operation

The surface area of the article is obtainedb7 direct measurement (this should be done

before the degreasing operation), and thecurrent to be used is calculated by makinguse of the figure given for current density.Thus, if the article has a surface area of20 sq. in., and the current density is ci.tamp/sq. in., then the required current willbe 20 x o.t = 2 amps. The article is sus-pended in the vat with the current switchedoff and the resistance set to its maximumvalue. The current is now switched on andthe resistance gradually decreased until theammeter indicates the appropriate value. Ifit is desired to inspect the article duringplating, the current must be switched offbefore the article is withdrawn from thesolution. If this precaution is not taken, avery high current density will be producedat the edges of the article and the platingwill be marred at these points. When theplating is completed, the article is removedfrom the bath and given a thorough rinse.The plating can now be brought to a highpolish by the use of a buffing wheel, or, ifthis is not obtainable, by the use of metalpolish on a soft cloth.

Formulae :-CopperCopper is rarely used as a final plating,

but is generally used as an intermediateplating. Since, however, the process andformula are quite simple and the chemicalsare comparatively inexpensive, I haveincluded details of the process here so thatit can be used as an initial exercise in elec-troplating.

Copper sulphate 4 oz.Sulphuric acid (conc.) r oz.Distilled water 2 pints.The copper sulphate is dissolved in the

water and the sulphuric acid added cautiouslywhile stirring the solution.

Plating is carried out at room tempera-ture and the current density employed shouldbe o.x amp/sq. in. The plating tame shouldbe 20-25 minutes. Two anodes of coppersheet are used.

This solution can be used repeatedly sincethe copper deposited on the cathode is re-placed by copper dissolved from the anodes.

NickelAlthough nickel plating requires a fairly

high current density, it is a process whichcan be carried out quite easily and effec-tively by the amateur when small articles areplated. The metal is softer than chromiumand the plating has a warmer colour. Nickelis often used as an intermediate plating oniron and steel in the operation of chromiumplating.

Nickel sulphateAmmonium chlorideBoracic acidDistilled water

4 Z.oz.oz.

2 pints.The plating bath should be used at a

temperature of about 90 deg. F. (32 deg. C.),and a current density of 1.5 amps/sq. in. Theplating time is four to five minutes. Theanodes should be pieces of nickel sheet, onebeing placed on either side of the cathode.As with copper, the plating solution can beused repeatedly.

ChromiumChromium is one of the most popular

metals for plating and there is no reasonwhy successful results should not be obtainedby the amateur if the instructions arefollowed. In the case of steel and iron,an intermediate coating of nickel will befound to be advantageous.

Chromic acid 5 oz.Sulphuric acid (conc.) 20 drops.Distilled water x pint.


May, 1953 NEWNES PRACTICAL MECHANICS

The operating temperature of the platingbath should be about 104 deg.F. (4o deg.C.),and the current density 0.5 amps/sq. in. Theplating time is to -i5 minutes. In thiscase anodes of lead are used, and after acertain amount of usage the bath will becomeexhausted. The quantities given above shouldbe sufficient for plating about i,000 sq. ins.,after which the bath should be discarded.

SilverThe amateur is advised to avoid silver

plating for two reasons. First, it is anexpensive process, and, secondly, the chemi-cals used in compounding the bath are ofan exceedingly poisonous nature. If anattempt at silver plating is made, great careshould be taken that the plating bath doesnot come into contact with any cuts or

abrasions .on the hands. At this junctureit might be well to say that many of thechemicals used in plating are of a corrosivenature and should be kept out of contactwith the hands, clothes, and so on. Abottle of household ammonia should be keptat hand, and if any of the plating solutionis accidently spilled, mopping up should bepreceded by a liberal application of theammonia. If a large quantity of platingsolution is spilled, it can be satisfactorilyneutralised by adding washing soda. (Vine-gar is a good antidote for caustic soda.)

Silver nitrate t oz.Potassium cyanide t oz.Distilled water II pints.

The working temperature of the bath is

321

68 deg. F. (20 deg. C.), and the currentdensity 0.2 amps/sq. in. The anodes shouldbe of silver, and the bath will last indefinitely.

Copper and brass can be plated directly,but iron and steel should receive an inter-mediate coating of copper before being silverplated.

ConclusionThe processes given above are not the

only ones which can be used. Other metalsbeside copper, nickel, chromium and silvercan be deposited electrolytically. It is alsopossible to deposit alloys, and, by suitablechoice of solutions, various grades of brasscan be formed. In general, however, theapplications of deposits of metals other thanthose outlined above, are outside the scopeof the requirements of the amateur.

Submarine Oil DrillingA Scheme for Drilling for Oil in the Sea Bed, Employing an

Aerial Ropeway for Carrying Men and MaterialsBY the end of this year the first major

submarine oil -drilling operation in theBritish Commonwealth from a plat-

form fixed on the sea bed will be underway in the South China Sea, about a mileoff the coast of British Borneo.

Initiated by Shell, the plari is to drill wellsinto the sea bed in an endeavour to find anunder -sea extension of the Seria oilfield,largest single oilfield in the British Common-wealth and now producing 5,000,000 tonsof crude oil annually. The under -waterextension of the field has so far beenexplored only by deviated wells drilled fromthe land and from platforms erected inshallow waters near the shore.

Four Wells from One PlatformFor this project, four separate submarine

oil wells can be drilled from a single fixedplatform. The foundation for the platformis a tubular steel jacket, which, prefabricatedin harbour, is carried out to a selected loca-tion and securely fixed in position on thesea bed. It is capable of supporting a weightof up to zoo tons.

The technique of drilling four wells fromthe same platform is designed to obviate theexpense of building a platform at each separ-ate location. One well can be vertical, andthe other three can be deviated, thus enablinga large area of the underlying formations tobe tested.

Two ProblemsThe setting -up of a platform sufficiently

rigid to permit drilling to proceed posed oneproblem. A second and, in this instance,even more formidable problem was to provideaccess to the platform itself during the longspells of stormy weather encountered in theSouth China Sea. Since vessels cannot bebrought alongside on account of the heavyswell experienced in this region for most ofthe year, a solution was found in the con-struction of an aerial ropeway linking thedrilling platform with the shore. By meansof this facility, constant communication canbe maintained with the platform, which hasbeen specially contructed to accommodate allthe equipment required for drilling.

Technical DescriptionThe drilling platform covers an area of

a 'oft. x 45ft., and is built on to a jacketcomposed of twenty-eight 24in. diametervertical steel guide piles tied together byhorizontal and diagonal bracings of angle

iron. The jacket rests on the sea bed in aboutSoft. of water, and befofe the drilling plat-form was erected steel bearing piles wereinserted into the guide piles and driven deepinto the sea bed until the required bearingcapacity had been obtained. Four rakingpiles have also been incorporated in thestructure in order to give greater stabilityand strength.

A special technique had to be employedfor assembling and placing the jacket. Itwas decided, therefore, to fabricate the jacketalongside the .shore in the sheltered river atKuala Belait and support it on two bargesclear of the water, each barge being equippedwith special framework Made up from Baileybridging. The whole assembly was thentowed out to sea and the jacket lowered on

to the bottom by means of winches. Thisoperation was carried out without incidentand, soon after the jacket had been loweredinto position, four corner bearing piles weredriven home by a steam hammer in orderto anchor it securely. This was necessaryas the main piling operation was a long joboccupying several weeks and was frequentlyinterrupted by unsuitable weather conditions.

The Aerial RopewayThe long span of the aerial ropeway con- '

necting the drilling platform to the shoremade it necessary to place intermediate struc-tures on the sea bed at 840 ft. intervals,these structures being supported on smallerjackets of a similar type to those employedfor the main drilling platform, each beingsecurely anchored by four bearing piles.Lifts of up to five tons for materials andequipment can be handled over the ropewayand a transporter car for personnel has alsobeen provided.

Royal. Dutch/Shell engineers were respon-sible for formulating the whole project anddesigning the steel structures and the drillingplatform.

Underwater drilling project in the South China Sea, off Seria, British Borneo. Four separatesubmarine oil wells can be" drilled from a fixed platform.



PLASTER CASTINGMaking the Master Forming the Mould : Casting Painting and Finishing

By E. S. WEERA

Fig. r.-A wall plaque in plaster.MAKING plaster models is an easy and

fascinating hobby. There is a readymarket for good quality work and

th's should well repay the initial cost.The following method of making plaster

wall plagues, statues, ornaments, etc., is wellwithin the scope and pocket of everyone. Inthe past the greatest difficulty in this kind ofwork has been in making a suitable mould ;but now there are a number of rubber orsynthetic resin products on the market whichsolve this problem for all. These mould-ing materials are melted and, when set, forma rubber -like, flexible mould which will wearlong enough for several hundred models to becast. The material can be melted down andused again and again.

Making the MasterWhile it is desirable to make models from

your own ideas and work, itis not essen:tial. A mould can be made for any small,non -porous object ; there seems little point,however, in merely copying something thathas already been made by someone else.

Clay, china -clay, plasticine or even puttycan be used to make the original model. Ofthese, plasticine is the best to use for thenovice modeller. If this is used it isnecessary to coat the finished job with threeor more coats of cellulose varnish. Thisholds the shape of the model long enough forthe hot, molten mould to take its form.

The wall plaque models illustrated inFigs. t and 2 were made in this way. Tryto model something from life, a good draw-ing, or photograph ; it is not nearly so hardas it seems, and after practice you will soonbe able to fashion a good likeness to the sub-ject. Use a reputable brand of plasticine.By warming, flattening out and rolling, itsoon becomes easy to work with and theonly tool required is a small, pointed stick,with which to put in tiny lines, marks, etc.

If clay is used it needs slightly more skillto produce a good model. The clay must bekept moist while modelling and be driedoff before making the mould ; it need not,however, be baked to hardness.

Putty is perhaps the most difficult to usebut quite good results can be obtained. Hereagain it is necessary to dry off the finishedmodel. Putty and clay can be used againafter making the mould ; plasticine, on theother hand, is usually melted and mixed upwith the cellulose skin. If a large model ismade it is possible to recover some of theplasticine by scraping off the cellulose.

The MouldAs previously mentioned, there are a

number of brands of flexible mouldingmaterials on the market. Prices range fromsix shillings up to 18 shillings per pound.Two pounds of low -melting -point mouldingmaterial were needed to make each of theillustrated models. These are roughly 6in. x4in. x tin.

Instructions as to melting temperature andsett'ng time are sent with orders ; but theprocedure is much the same for most kindsof th's product.

Before melting down, the moulding com-pound looks and feels like medium hardrubber blocks or slabs. It is necessary to cut

Fig. 2.-Another plaster wall plaque.

these up into smaller pieces and drop theminto a saucepan.

It is very important not to melt quickly ;a very low gas or electric stove will do thejob admirably. The product will give offa strong rubber -like smell but, generallyspeaking, it will only give off fumes whenover -heated.

A low gas will satisfactorily carry out themelting in 20 or 3o m:nutcs, but the timevaries acording to the type of material used.By using a full gas it can be melted in afew minutes but will then be burnt and toohot to pour. If you do not have a thermo-meter the best and safest policy is to takeplenty of time over melting.

The liquid should be sfrred gently witha clean stick or rod. While the melting isgoing on the master model can be madeready.

The clay, putty or plasticine model willhave been dried or cellulosed and the nextstep is to place it in a box, which can bewood, tin or even strong cardboard. Anordinary cooking dish or bowl can also beused for this. Makc sure that there areno holes in whatever is used to hold themould. Any holes which do exist can beplugged with putty or plasticine.

After completely melting the compound,take it off the gas and allow it to cool downfor a few minutes ; this will prevent thehot liquid from bubbling when it is pouredon to the master. After making certain that

the model is flat and firm against the bottomof the box, take a round stick or rod andhold against the lip or side of the saucepan.

The liquid should then be poured downthe rod quickly (see Fig. 3), and into onecorner of the box ; not directly on to themaster. At first there may be slight bubbling,but this should soon stop, and the liquidbegin to set. Tiny air bubbles will probablyform round the sides of the box. These canbe ignored, but should they form over themodel itself, they can be burst by jabbingquickly with a needle. If there are too manyto burst, it is a sure sign that the liquidhas not been cooled down enough. Withmoderate bubbling it is still possible to get agood mould but the top surface will bepocketed with holes and tiny bumps.

Three to four hours should elapse beforeattempting to take the master model fromthe mould. This is done by running asharp knife round the box, pressing themould with the fingers away from the wallsof the container, and then by turning oversame and gently knocking the bottom. Themould, complete with model, should thenslide out.

By flexing the mould the model can bewithdrawn. If this is plasticine, it mayleave traces inside the mould which must beremoved with a soft cloth. A clay or puttymodel will pull out cleanly and will be inthe same condition as when made.

It may be necessary to split the mould. Astatue or similar ornament will need thistreatment, but it does not require halving.One side of the mould can be cut with asharp knife and the mould flexed to allowthe model to be eased out. (See Fig. 4.)

A split mould will still hold the liquidplaster if it is held together by rubberbands, making sure that the joint matchesup cleanly.

CastingHaving made the mould the next stage is

casting a plaster replica of the original model.Fine white plaster is used, costing a fewcoppers per pound; one pound will makeseveral models.

The plaster is mixed in a suitable basinand added to the water ; do not add water

Fig. 3.-Using a rodfor pouring themoulding compound.



4.-Splitting theflexible mould.

to plaster or great difficulty will be experi-enced in mixing properly.

For a model of the size illustrated, onetea cup of water is sufficient. To this wasadded seven tablespoonfuls of plaster, onespoonful at a time. Each helping of plasteradded to the water should be quickly andthoroughly mixed, in before adding any more.

It is advisable to mix' the plaster quicklybecause it reaches the . stage when it willrapidly begin to set and harden. It shouldstill be liquid when poured into the mould.If it has begun to set,- it will not flow intoevery corner of the mould, 'and a modelwith holes or parts -missed off will beobtained.

The mould must be laid on a flat surfacebefore it is filled with plaster. After pour-ing in the plaster quickly a brief shake ofthe mould will get rid of any air bubbles.

A wall plaque may have been made, inwhich case a hook will be required in thefinished job. A good method is to bend apaper clip and simply drop it into the liquidplaster. The plaster will set hard and theclip be cast in, the bend in it preventing itfrom pulling out when the plaque is hungon a wall. (See Fig. 5.)

In ten minutes the plaster should havehardened and is now ready to be takenfrom the mould. Due to it still being wet,the model will break rather easily, and alittle care is needed here.

With the finger tips gently flex the mouldaway from the plaster, gradually working itoff the model. In the case of flat objects,such as wall plaques, calendars, or similarthings, all that is required is to place one

Fig. 5.-Method of fixin; a hook for supportinga plaque.

mould and carefully bendone end away from the model. (See Fig. 6.)

The plaster model is dried in a low gasor electric oven. It can also be satisfactorilydried by placing before -an open fireplace oreven in the strong sunlight, The one thingto remember is that if the drying is donetoo quickly, the model is liable to distort andmost certainly- to crack. Having got thisfar, it is wiser to take' three or four hoursin slowly drying the model.

Painting and FinishingNo matter how well cast a plaster model

might be, it can be completely, and horriblyspoilt by haphazard, careless painting. Abadly -cast model, however, is vastlyimproved, the faults hidden, by carefulpainting.

Ordinary, water colour, poster or cellulose

hand under the

paints will take on plaster. Of these, watercolours combined with poster paint give thebest results and also the widest range.

Should the model be of an animal orsomething from life, a common-sense studyof the real thing will make it easy to decidewhich colours to use.

Plenty of water is needed with poster andwater colour paints. The plaster will absorbthe water and, after painting, it should bedried for about twenty minutes. A coat ofclear cellulose varnish brushed on the driedmodel will preserve the colours and finishthe model off. The models illustrated werepainted in this way.

Cellulose paint can be brushed straighton to the model, and no other treatmentis required. This is the best paint to usewhen the effect needed is that of one or twocolours only.

Ordinary paints will give good results buthave the snag of taking a long time to dry.Here again, a coat of clear varnish can beapplied to the finished job.

There is no limit to the things that can

Fig. 6.-Bending the mould away from the cast.

be made from plaster or to the effects thatcareful painting can give. Aim at life -like-ness, 'unusual design and original ideas.

B.R. New Hopper WagonTo meet the requirements of bulk convey-

ance of chemicals suzh as soda ash,sodium tripolyphosphates or catalysts, thiswagon has been designed at Derby, and toobtain the maximum Capacity within a totalgross load of 35 tons, the body takes fulladvantage of the loading gauge.

The length of the vehicle over buffers is24ft. 6in. and the wheelbase is soft. 6in.

The underframe is of special design toaccommodate the hoppers through which theload is ejected between the frames. It is ofall -welded construction and is 2Ift. 6in. longwith standard buffing and drawgear with threelink couplings. The wheel diameter is3ft. 'lin. with loin. by 5in, journals andfabricated steel axleboxes. Standard lamin-ated springs 3ft. 6in. long are fitted withstandard spring shoes.

The most recent design of. brake used canbe applied from either side of the van andoperates one block on each wheel of one axle.

The body is of welded construction and isbuilt up of *in. mild steel plates for the roofand sides whilst kin. thick plates are usedfor the ends and the hoppered portion of thebody. Tee sections and gusset plates stiffenthe body and are welded to the underframe ;the combined body and underframe givingadequate strength and stiffness. A kin. thickpartition divides the body into two compart-ments and two 2 -hinged doors 6ft. t sin, longand 2ft. 5in. wide are -provided in the roof,fitted with rubber weather seals and secured

by screwed eyebolts. A roof vent is usedwith or without valve, according to traffic, anda cat walk is a'so provided to give readyaccess to the filling doors. The interior itcompletely flush and the hoppers can becompletely discharged by gravity through two

sliding doors per compartment. The openingmechanism for each door is a rack and pinionoperated from either side of wagon by aremovable handle. The doors can be sealrdby wire seals.

In the case of soda ash or sodium tripoly-phosphate a coupling of a quick detachablevibrator is welded to the sides of the hoppersto assist unloading.

The new hopper wagon for British Railways.



THE grpapiEJ OF

fftfilteV T°The Reasons for Sweptback Wingsand the Problems Which TheyIntroduce. Delta, V and Crescent Wings,and Possible Shapes for Supersonic Speeds

BETWEEN 1939 and 1945 we, in theUnited. Kingdom, were too busy win-ning the war to do as much funda-

mental research in aerodynamics as, we oughtto have done. The Germans, rather curi-ously, found time to do much more basicresearch, and if the war had continued muchlonger we should have found ourselves in adifficult position against the rocket propelled,swept. wing fighters which were just begin-ning to come from the German aircraftindustry.

War always provides a stimulus to techni-

cal advancement, but in this country thebiggest strides in the aerodynamic field havebeen taken since the war and were the directconsequence of jet propulsion, which made it

" The Shape of Wings to Come" wasfirst presented as a paper by DavidKeith - Lucas, B.A., M.I.Mech.E.,F.R.Ae.S., Chief Designer at ShortBrothers, Rochester, in Belfast, Septem-ber, 1952.

Fig. 3.-The Hill Pterodactyl of 1925.

Fig. I.-Hurel-Dubois HDio with aspectratio of 321.

possible to fly at higher speeds and enhancedthe importance of being able to do so.

Germany had reacted sooner than we tothe challenge of jet propulsion and we owe alot to the lead given to us by the Germanresearch work. It is healthy, if a littlefrightening, to recall that Lippisch, in Ger-many, was working on a high-speed deltadesign even before the last war.

It is intended to review the reasons whichhave led to the sweptback, crescent and deltawing forms and try to see where thesedevelopments are leading us.

I shall deal mostly with high-speed air-craft, although recent researches have led toat least one rather intriguing shape for lowspeeds, namely the Hurel-Dubois light 'planewhich is shown in Fig. I. As will be seen,the wing of the Hurel-Dubois has a verylarge span and small chord. Its aspect ratio,that is, the ratio of the span to the meanchord, is 321 compared with a maximum ofabout 12 on the wartime bombers and aboutfour on modern fighters.

Fig. 4.-All wingair liner projected

in 5945 -

It is quite possible that it may be theforerunner of others like it, and it is includedhere to show how low -speed aircraft aredeveloping in comparison with high-speedtypes.

Before the war the difference between ahigh-speed and low -speed aircraft was mainlyone of degree. They were both flying atsubsonic speeds and aerodynamic laws werethe same for both. The high-speed aircrafttherefore had more power and less drag, butwas not necessarily very different in outwardshape, from one designed for low speed.

To -day the picture is quite different,because by "high speed " we have come tomean that the aircraft flies at supersonic or,at least, very high subsonic speeds, and, bypassing through or even approaching thespeed of sound, it has entered a new regimeof aerodynamics. It is a natural corollarythat -the aerodynamic shapes have to bedifferent, too, and as aircraft speeds increasewe can expect a continuing divergence be-tween the design of " low speed " and " highspeed" types.

The Purpose of SweepbackThe outstanding development in high-

speed aircraft is the swept wing in its differ-ent guises.

It is often stated that sweepback enablesa wing to " slide " through the air in ratherthe same way as a bread knife or a scytheis drawn across what it is cutting. This,of course, is the principle of the guillotine,which always had a swept back or " delta "blade. But we are talking of air, whichbehaves differently from bread, grass or thehuman neck. Indeed, the analogy is dan-gerous, if not actually misleading, for at low

Fig. 2.-Diagram of a swept wing in a windtunnel.



SLOT

a 02 04 06 oa to

2

Iy

CHORDAL POSITION

Fig. 5.-Suction wing aerofoil section.

speeds the drag of a swept wing is no lessthan that of a straight one; the advantageis only at high speeds.

Perhaps the best way to illustrate thepurpose of sweepback is to take a rather far-fetched example from a wind tunnel. Let ussuppose that we have an untapered wingwhich spans the tunnel and, if you like,sticks out a bit at either side. The tunnelspeed is 400 mph and the pressure distribu-tion round the wing is, clearly, appropriateto its incidence to the airstream and to thespeed.

Now let us suppose that the wing is mademuch longer, so that it sticks a long wayout from one side of the tunnel, and that weproceed to push it through the tunnel at30o mph at right angles to the airflow.Apart from some slight corrections due toskin friction, the pressure distribution overthe wing is unaltered and is still that appro-priate to 400 mph. But if we consider anyone point of the wing it is, by simple vectors,in an air stream of 50o mph to which thewing is swept back at tan - or about35 deg. This is shown diagrammatically inFig. 2.

The flow round the wing is thereforebehaving like that round a straight wing at40o mph, whereaS the actual speed is 500mph. An aircraft with swept wings cantherefore fly much faster than a correspond-ing one with straight wings before meetingthe compressibility troubles which, on astraight wing, occur at and around the speedof sound. These troubles include increaseof drag, loss of lift, changes of trim,deterioration in stability and control, andalso the possibility of unpleasant buffeting.

This explanation really amounts to nomore than saying that we can resolve thevelocity into two component's, cne at rightangles to and the other along the wing, andthat we can then neglect the flow alongthe wing. For some strange reason mostpeople find the wind tunnel analogy easierto visualise.

In practice, due to boundary layer and endeffects, the advantage that can be realised isonly about half of that indicated by thisover -simple treatment. But, in spite ofthat, sweepback hastwo very importantcontributions to offer.In the first place, itreduces the adverseeffects of compressi-bility and in thisrespect a swept wingbehaves in much thesame way as a muchthinner, straight wing.In the second placesweepback postponest h e compressibilityeffects to higherspeeds and, if theangle of sweep is suffi-cient, can even post-pone them to speedswell above the speedof sound, which issomething which thin-ness by itself cannotdo.

Both contributionsare important, but the

second one is particularly important if theaircraft is designed for a maximum speedanywhere between, say, 8o per cent. and15o per cent. of the speed sound, i.e., for amach number between o.8 and 1.5.

All -wing AircraftNow sweepback was first introduced into

aircraft design for quite a different reason.With the development of cantilever mono-planes designers began to think in terms ofthicker wings and explored the possibility ofusing aerofoil section of up to 25 per cent.thickness : chord ratio, As the size of theaircraft increased it became tempting to tryto submerge the fuselage by putting itathwartships, in the wing, so saving theweight and drag of the fuselage. It alsoreduced the bending moments at the wingroots, arising from the upward lift forces,by spreading the load more uniformly acrcss

Fig. 6.-Australian suction wingthe span. The obvious development of thisidea was to dispense with the tail becausethere was no longer anything to support it.The longitudinal stability and control ofthe aircraft was then restored by sweepingthe wings back and, in effect, carrying thetailplane on the wing tips.

The Hill Pterodactyl, of 1925 was apioneering effort in this direction and isshown in Fig. 3, from which it will be seenthat although there is still a fuselage it isonly a small one. Fig.4 shows an exampleFig. 7.-(Below) Pro-posal for a suctionwing air liner.Fig. 8.-(Right) Air-craft with delta wing-

Avro 707.

of a design which was projected by ShortBrothers in 1945 as a transatlantic airlinerto much the same specification as the Braba-zon. With a wing of 22 per cent. thickness :chord ratio, it had to be a very largeaircraft to provide sufficient headroom in thecabin.

On paper it showed an advantage in pay-load and speed over a conventional design,but the passengers' view would have beenpoor and the stability and control problemsneeded further investigation.

Boundary Layer SuctionOne of the objections to using the thick

wing sections demanded by this sort ofdesign is that the drag of the wing becomesunduly high. A thick boundary layer ofrelatively stagnant air builds up round thewing and is shed as a wake from the trailingedge. The drag can be very much reduced

if this boundary layer

glider.

is sucked away nearthe trailing edge ofthe wing and it be-come.] possible to usevery thick sections,such as that shown inFig. 5, without incur-ring any penalty indrag over normalthin sections. Theengineering difficultiesare considerable asthe quantity of airwhich has to be re-moved is very large,but it can be done,and it makes the all-w:ng design bothfeasible and attractive.

Fig. 6 shows anexperimental glider

developed and flown by the AustralianAeronautical Research Laboratories.

It has a wing section of 311 per cent.thickness : chord ratio with boundary layersuction. In a lecture before the ThirdAnglo-American Aeronautical Conference,Mr. T. S. Keeble explained that the experi-ment was directed towards an all -wing airliner and that, basing the design on theresults of the glider tests, he calculated thatsuch an air liner could carry 4o per cent.

more load 4o percent. taster than onedesigned on conventional lines, while stillconsuming no more fuel for the same range,offering a large advantage in operating costs.

Fig. 7 shows the general arrangement ofKeeble's air liner. It is an attractive pro-position and looks like a high-speed aircraft,although, in fact, it cruises at under3oo mph.

Alternatively the same devices may be



used to obtain wings of very high aspectratio like the Hurel-Dubois, but without theneed for the strut and therefore of lowerdrag.

The great problem with such slender wingsis to provide sufficient stiffness and strengthin the wing structure without making it tooheavy, and 'so cancelling the aerodynamicadvantage. The thicker sections possiblewith boundary layer suction make the ideamore practical and it becomes very attractivefor low speed, long-range aircraft, and espe-cially for those which require -long enduranceas opposed to range, as, for example, CoastalCommand aircraft engaged on anti-submarinepatrol.

Tailless AircraftWe have got so used to the conventional

arrangement of aircraft with a straight wing,a long, slender fuselage and a tail, that weare apt to look on a tailless design as some-thing of an unnatural freak. But if weobserve nature carefully we notice that sea-gulls and ducks and many other birds are,in effect, tailless, at least in straight flight,and bats are taillessat all times, and areprobably the mostmanoeuvrable of allfliers. Gulls usetheir tails inmanoeuvring but, asfar as one can see,more as air breaksthan as elevators,a n d, incidentally,they use their feet inthe same way. ,

There is a strongargument for a tail-less design on struc-tural grounds. In apull out from a diveor a high-speed turnthere is a large up -load on the wing andusually a download on the tail. On a con-ventional -tailed aircraft with sweptback wingsthe moments due to these loads cancel eachother out only through the long path up thefuselage and the wing to the centre section.With a tailless design, on the other hand, thedownload of the tail occurs at the wing tips,and so we not only avoid the need for astructurally strong and stiff fuselage butreduce the bending moments in the wingsalso. There is therefore a potential gain instructure weight as well as in drag, whichmust be offset against the fact that the tail-plane, if we may call it that, has a shortermoment arm and therefore has to be larger.

aircraft. In America the controversy betweenthat type of design and the high aspect ratiowing with a long, slender fuselage has beendubbed the " big wing " against the " bigstick " and long-range bombers have beendeveloped to both formula. Both types ofaircraft were designed for relatively lowspeeds. As the speeds of military aircrafthave increased, the old controversy has diedaway and a new one has come to take itsplace. The new argument is between thedifferent rhapcs of swept wings, and thebig wing and big stick appear now as thedelta wing and the sweptback or V wing asused on the Boeing B47 and B52 and on theConsolidated B6o jet bombers. These twotypes are shown in Figs. 8 and 9.

Aero-elastic EffectsWe have already seen how sweepback was

first introduced as a means of providinglongitudinal stability and control on taillessaircraft. The odd part of the story is thatnowadays we are concerned with the ill-effects of sweepback on stability, both longi-tudinal and lateral. It seems as if it had

Fig.

Delta or V WingsEven without bondary layer suction there

is a good case for the all -wing and tailless

a-undeflected.

9.-Aircraft with V wing-Boeing B47.turned about and was now kicking for theother side; but still, if we keep a carefuleye on its behavioUr it is very well worthits place in the team for its high-speedqualities. The instability in its charactershows itself in various ways, of which themost pernicious are aero-elastic effects, tipstalling and rolling moment due to sideslip.It is the aero-elastic effects, the aerodynamiceffects of structural distortion in flight, whichoften have the biggest influence on the choiceof wing planform.

The fact that the sweepback is employedto allow high-speed aircraft to fly at stillhigher speeds is, in itself, a fair indicationthat we are likely to meet severe aero-elasticproblems because at high speeds even quitesmall distortions may give rise to large aero-dynamic forces.

Aileron ReversalAn example of the sort of problem that

I have in mind is the designer's old bug-bear of aileron reversal. Consider, say, thestarboard wing of an aeroplane on which theaileron is deflected downwards with the in-tention of increasing the lift on that side andmaking the aircraft roll to port.

On a perfectly rigid wing the resultantrolling moment would increase as the squareof thespeed, but in practice wings cannotbe perfectly rigid and the behaviour is morecomplicated. The air loads due to the down-ward aileron .produce a twist in the wing,up at the trailing edge and down at thenose, so that the wing loses incidence andloses lift and so produces a rolling momentwhich is in the opposite direction to thatdue to the aileron itself.

The amount of the twist increases withspeed because the air loads become greaterin comparison with the elastic restraint ofthe wing structure. Finally, there comes aspeed at which the rolling moment due tothe twist equals that due to the aileron andthe ailerons become totally ineffective.

At still higher speeds the effect of the twistexceeds that due to the ailerons and theaircraft rolls in the opposite direction to thatintended by the pilot.

The designer has to see that the " aileronreversal speed " falls well outside the opera-ting speed range of the aircraft and to dothis he may have to make the wing muchstiffer in torsion than would otherwise benecessary.

Aileron reversal is a problem which waswell known in the days of straight wings,but sweepback has made it a more subtleenemy. Not only must we now considerthe stiffness of the wing in torsion but also wemust see that the bending deflections do notcause a loss of aileron power. It is not imme-

why this should happen.The best way to see it is by deflecting an

actual model. Fig. ma shows a model of asweptback wing. The pointer at the tipshows the incidence of the wing in the lineof flight. The two vertical rods show whetherthe wing is twisted along its span. In Fig.ioa the wing is undeflected and untwisted.In Fig. sob a load applied centrally at thetip has deflected the wing while leaving ituntwisted but, as the pointer shows, thereis a severe loss of incidence at the tip. Thisin turn means a loss of lift which opposesthe intended effect of the aileron. Thischaracteristic of sweptback wings may, aswe have seen, produce a serious loss of aileronpower but cannot, by itself, produce aileronreversal because the effect dies away tonothing as the aileron power diminishes.

(To be continued.)

Fig. to.-Distortion of a model sweptback wing.b-untwisted but with loss of incidence c-no loss of incidence at the tip, but the

at the tip. wing is twisted.


May, 1953 , NEWNES PRACTICAL MECHANICS 327

for the Amateur Photographer

The completed grease -spot photometer.

THE instrument described below is similarto a commercial grease -spot photo-meter and can be constructed for little

outlay by the average home mechanic, asno doubt most of the required componentswill be found in the oddments box.

Basically, it consists of an electric bulbfixed below a grease spot, the brightness ofthe bulb being regulated by means of a vari-able resistance. If such a system is placedbeneath another light source the grease spotwill either appear light against a dark back-ground or dark against a light background,depending upon whether the upper lightsource is weaker or stronger than the lowerone. By altering the brightness of the lowersource the grease spot fades into the back-ground, and at this point the relative inten-sities of the two sources are equal. Henceit is possible to measure the intensity of theupper source.

To obtain as great sensitivity as possiblethe range of brightness controlled by thevariable resistance should be spread over asgreat an arc as possible. This is arrangedby choosing a value for the fixed resistancesuch that it cuts down the brightness of thelight to about the greatest that will berequired for normal enlarging purposes, andusing a variable resistance of such It valuethat it dims the light to almost zero over anarc of about 18o deg. This represents anexposure range of about 3o minutes on thefinal scale prepared for the instrument.

The values of the resistances ; so ohmsfor the fixed and 25 ohms for the variableone are not claimed to be the most effective,but gave in the original instrument a fairlylong scale as mentioned in the previousparagraph, when an initial voltage of about5 volts was used.

The blue filter was included to compensatefor the greater percentage of red lightemitted by the low voltage bulb comparedwith the normal enlarging bulb, and also toenable the balance point to be arrived atmore easily.

The actual filter used, was the pale bluecompensating one supplied with Dufay-color, but a piece of celluloid tinted withphoto tints or a square of blue gelatine(iix exposure as used in portraiture) maybe purchased.

If the photometer is to be used in con-junction with a voltage control unit the switchmay be omitted, it only being necessary if abell transformer is used,direct on to themains.

Filter MountThe filter mount is of card and the same

size as the ring used in the grease spotassembly.

Preparation of theGrease Spot

The grease spot itselfis made by dropping candlegrease on to a piece ofart paper and scraping offthe excess grease. It isbetter to prepare a fewsuch spots on one piece ofpaper and to retain anduse the best specimen,which should be about *in.dia. and symmetrical.

A celluloid ring and discas shown in Fig. r areprepared and after paintingone surface of the ringblack the three parts arecemented together, asshown.

Fig. 2.-Circuit diagram of control unit.

As the cord is opaque, and mounted closeto the bulb, it serves to restrict the beam oflight reaching the grease spot.

AssemblyThe wooden base and ends and the

aluminium top and sides, were given a coatof black cellulose after being drilled to takethe various components.

Wooden ends washerInsidating Aluminium

.1a baseora........4.t.aiop )(ides

Grease spot assemb/

A Grease-spot PhotometerConstructional Details of an Inexpensive Instrument;

By W. L. PEACOCK

To save space the bulb -holder was dis-mantled, only the threaded portion, thesoldering tags and the insulated spacingwasher being retained. These parts were thenfixed to one end with a wood screw, asshown.

The other components can now be added,care being taken to adjust the height of thefilter so that it is just above the bulb.

The switch, if used, fixed and variableresistance and bulb are now connected inseries, the leads being taken direct to thevoltage control unit or the bell transformer.

It will be noted that a lug has beensoldered to the locking nut of the scale toensure ease of locking.

Voltage Control UnitThe photometer as described here origin-

ally operated from dry batteries, but if anA.C. mains supply is available it may beconnected to this via a suitable bell trans-former.

The control unit, Fig. 2, consists of a toohm variable resistance, a voltmeter fittedwith a plain scale with a mark at about 5volts, a switch and a 6 volt dry battery. AnEver -ready 6 volt battery, No. 996, willsupply current for this instrument for a fewyears before its voltage drops to the mini-mum required for its accurate operation.

In practice, the power supply is switchedon and adjusted to the mark by means of thevariable resistance when the variable resis-tance in the photometer is fully out of cir-cuit, i.e. the lamp is at its brightest.

It could equally well be set with theresistance fully in the circuit, so long as thisprocedure is always adopted.

CalibrationThe method of calibration is to use the

height of the enlarger head above the easeland the iris to obtain a series of lightintensities one-half of the previous one. The

Small pointer for Pointer knobf/2 dia. hole Paper speeds Plate soldered to lock

2T-41nut to provide easy

locking of dial

r1 ." '4Ellue filter attached -== = -L- 1'., to card ring

4v.3a. bulb-._,_--7.-

____

.kCelluloid disc .743" dia. '

ContactsLampholder

Celluloid ring outsidedia. z$" inside dia. leOne surface painted

.black

Grease spot about ledia on art paper

Variable resistance 25.n.

1-*

Toggleswitch

Leads tovoltagecontrol

unit

Fig. 1. -Details of celluloid disc Fig. 3.-Sectional elevation and plan of the grease -spotphotometer.and ring, and grease spot disc.



spot is balanced out for each setting andthe position of the knob marked on a dummyscale.

Prepare a dummy scale (2in. dia.) andattach to the photometer, locking it inposition with the lock -nut provided ; replacethe pointer knob.

Set the voltage control unit as alreadydescribed and with the enlarger head in thelowest position in which it is used inpractice, open the lens to the first " whole "stop number and throw slightly out of focus.Place the photometer in the centre of theeasel and balance the two light sources .bymoving the knob until the grease spot is notvisible against the background.

Under these conditions the intensity of thelight from the enlarger will never exceedthat used in practice, as with a negative inposition even in the highlight there will besome cut in the intensity. If a bulb ofhigher voltage is substituted later, however,it may not be possible to balance the spctwith the head in this position and the lenswide open.

Care must be taken to ensure that a seriesof stops are used which will give half thelight intensity of the previous one. Twomethods of marking are in general use, theEnglish and Continental, a suitable series ofstops being 2.8, 4.o, 5.6, 8, I1,-16, 22, and3.2, 4.5, 6.3, 9, 12.5, 18, 25, respectively.If any intermediate values are employed thescale about to be prepared will not be linear.

When balancing out the spot for eachsetting of the light intensity it is desirableto approach the balance point from each sidein turn, and to take the average value asthe actual point recorded.

After marking the first point, close thelens one whole stop and balance again, con-tinue until the lens is fully closed.

Next, reset the pointer back one divisionand opening the lens to the original stopused, raise the enlarger head until a balanceis obtained, close the lens one stop andrebalance, proceed as previously describeduntil about 12 points have been made.

By setting the pointer back one divisionbefore rebalancing by raising the enlargerhead it is possible to check the accuracy ofthe last mark.

When a sufficient number of points havebeen recorded remove the scale, draw radiallines through each mark and measure theangle subtended by each pair.

Total and average the results. Anydeviation from the average is due to thenon -uniformity of the variable resistanceemployed.

Next prepare on a piece of plain cardand mark off 6 deg. intervals along itsedge, so making 6o divisions, which willeventually be used as paper speeds ; numberas shown in Fig. 3.

Using the average angle subtended by eachpoint on the dummy scale mark off a con-centric scale in such a position that thepointed knob is just in line with it, andnumber the points I 2, 4, 8, 16, 32 (secs.),I, 2, 4, 8, 16 (mins.) as shown in Fig. 3.

Cement the finished scale between twopieces of celluloid and fix it to the photo-meter.

Determination of Paper SpeedsThe speed of any type or batch of paper

is determined as follows:Set up the enlarger with a negative most

suited to the type of paper whose speed isbeing determined, and make an accurate teststrip using the middle tones of the negative.Develop, wash and fix in the usual way, anddecide the correct exposure by examinationof the strip in white light. If a test stripholder of the type which exposes a small

square of a piece of paper, in turn in thesame position each time, is available, thecalibration will be all the more accurate, asthere can be quite a variation in tone alonga large test strip. Alternatively, test stripsof the shadow and highlighter can beprepared and the average exposure used.

Now place the photometer on the easel inthe position occupied by the test strip at theportion of it which was correctly exposed ;balance out the spot. Leaving the knobin this position unlock the scale and rotateuntil the correct exposure required is inincidence with the pointer, then lock thescale. The paper speed may now be readoff against the pointer on the outer scale.

To obtain the correct exposure for anyother negative printable on this paper takea reading on the middle tones or an averagewith the dial set at this particular speed,and read off the exposure required againstthe pointer at the balance point.

Measurement of Contrast RangeThe comparison of the contrast range of

a negative with that of available papersenables the most suitable grade to be chosen.

The contrast range of the negative isdetermined by taking a highlight and shadowreading and expressing the results as a ratio:

Highlight reading ... soShadow reading ... 48oContrast range ... 48:1

To determine that of paper, raise theenlarger head high up on the column, stopdown the lens slightly and throw out offocus. Using this dim light source, placea strip of paper on the easel and prepare agrey scale, each section receiving twice theexposure of the previous one: Ex. 5, to,2o, 4o, 8o, 16o and 32o secs, may be used.

Develop, rinse and fix the test strip.The ratio of the exposure required for the

last pure white divided into that requiredfor the first pure black gives the contrastrange of the paper.

Contrast range:Maximum exposure for pure white.Minimum exposture for pure black.

Plastic Thread HolderThis Device, Submitted by Mrs. M. Garrick, Won

Recent £200 Prize CompetitionWHILE looking at my card of tangled -up

stocking threads, the idea came to mymind that if a container were available toseparate the different shades of threads andalso stand up to a lot of rough handling it

Snap clip

a Prize in Our

drical shape and hinged to open, as in thesketch. The various shades of thread onspools could be placed in the lower half,each spool in a separate compartment. Thefree ends of thread could be fed through holes

Hinge

The plastic thread holder(shown open) and an end viewshowing the thread -clamping

lever.

would save a lot of time and frayed tem-pers. This magazine type of holder wouldbe suitable for workbaskets or handbags. Ithink it could be made of plastic, of a cylin-

Lever clampingthread againstcylinder body

1 Lever in the\ thread released\\position Pi-

END VIEW

above each reel to the outside of the top halfof the case, the protruding thread being stop-ped from moving, except when required, by alocking rod, as shown in the diagram.

0 KS

Screw Thread Tables, SP., by post 5/3.

Refresher Course in Mathematics, 8/6, by11/-.

post 9/-. Wire and Wire Gauges (Vest Pocket Book), 3/6, by

Gears and Gear Cutting, 6/-, bypost 3/9.

post 6/6.

Workshop Calculations, Tables and Formulae, 6/-,Metric and Decimal Tables, 3/6, by post 3/9.

by post 6/6. Practical Motorist's Encyclopaedia, 17/6, by post 18/,

FROM GEORGE NEWNES, LIMITED, TOWER HOUSE, SOUTHAMPTON STREET, STRAND, W.C.Z.

FORBy F. j.

ENGINEERS--------.CAMMDictionary of Metals and Alloys, 10/6, by post



Modern Inventions andNew Ideas Exhibition

Some of the More Interesting Exhibits at the Recent ShowTHE Modern Inventions and New Ideas

Exhibition opened recently under thepatronage of H.R.H. the Duke of

Edinburgh contained much of interest in asmall space.

One presumes that the sub -division of"New Ideas " was an afterthought to coverthe large number of commercial stalls sellinga diversity of novelties from tubes of plasticfor blowing bubbles to a new and very effi-cient needle -threader.

The " New Inventions " section was underthe auspices of the Institute of Patentees, ofwhich Professor A. M. Low is president." Unhappily," said Professor Low, as usualmaking a great deal of sense, " the inventorseldom receives more than honour. Yet itis of ten from the humblest beginnings thatcommercial sucess has sprung. This exhi-bition sets out to show how, by concertedeffort, inventors can be encouraged."

There has long been a need in this coun-try-whether Government sponsored orprivate-for some central organisation tohelp inventors on their way. Most of themare befuddled with the intricacies of patentlaw and are awed by the cost, operating ona rising scale, of attempting to protect theirproperty from the machinations of unscrupu-lous persons. Obviously, no individual canafford the kind of litigation that ensuedright up to the House of Lords such as thatin which the Raleigh Industries' " Dynova "patents were eventually set aside.

By THE MARQUIS OF DONEGALL

In the inventions part of the exhibition anumber of recent industrial inventions ordiscoveries were displayed. One develop-ment was in the use of the cathode-ray tubeto reduce the regulation of watches from daysto minutes by making the " tick " visible. AsI sauntered along a rotary machine was

vented hexagonal chess, played on hexagonsof three colours. I am open to correctionfrom infuriated chess players, but I believethat this gives the King twelve possiblemoves, the Queen twelve directions and theKnight twelve possible cells-or squares, asthey would be in the old game. All that Ican say about it is that it would appear to benot quite as bad as three-dimensional chess,

which I once saw demon-strated, or playing against

(Above.) Mr. W. Glinski, of London, with his newinvention of Hexagonal Chess. By employinghexagonal cells instead of square the movements

of the chessmen have been increased.(Left.) A new Ironing Chair which was demon-strated at the exhibition. A tubular steel cranklinks the ironing board to an ordinary chair, enablinga person to sit in a comfortable position. Invented

by Mr. J. Vickery, of Croydon, Surrey.

replacing broken -off handles ontea -cups at the rate of twentya minute.

Another part of the exhibitioncontained individual models byabout a hundred inventors.These were displayed in thehope of catching the eye of thepotential commercial sponsor.

Cyclists' hand -signals and astop -light for the bicycle wereuseful and topical contributionsand, while on the subject ofaccidents, mention should temade of the deck -chair that isguaranteed not to collapse.

Chess ImprovementsAs though checkmate were

not already a difficult enoughoperation, somebody has in -

a machine which wasguaranteed to win, as Ionce did at an exhibition inGeneva. Not the least in-furiating part of thismachine, which was theinvention of a Spaniard,was a metallic voice fromthe machine's inside whichcried " Jaque al Rey! "every time it was check;added to which, if youtried to move into check,the machine said in Span-ish, " You can't do thatthere 'ere," or words tothat effect.

Housewives would ap-prove of the ironing -chair-indeed, I have oftenwondered why it has beenthought necessary to makeironing even more tediousby standing up to do it.Improved Car -park

The mechanised car -park, of which there wasa scale model to be workedby turning a handle, was.one of the best things inthe exhibition.

One mechanised sectionor unit of the car -park wasshown, and there couldpresumably be any numberof these 'units for whichspace is available. Eachunit takes twenty cars onan endless belt. The timecalculated for releasing anygiven car is one and a halfminutes, and it is reckoned

that three hundred cars could be parked onthis system where previously only twohundred could be stored with any degree ofworking practicability.

Even with two hundred cars the averagetime for releasing the least -convenientlyparked vehicle would be seven or eightminutes. One can only hope that this inven-tion did, in fact, find a sponsor through theexhibition.

Still in the Inventors' Section, there wasan anti -dazzle screen, with a cut-out sectionfor looking through, while the remaindereliminates the glare. Another device Inoticed was an animal controller, for clamp-ing the noses of such animals as bulls as animprovement on the usual nose -ring. Theegg -boiler, which automatically switches -offwhen the eggs are ready, seemed a usefuldevice, as did the very simple idea of the



bread -board with a slit to keep the knifestraight, thus ensuring a regular slice.

Home ImprovementsA compact unit to supply hot water, warm

air for space -heating, and ventilation, wasone of the many exhibits contributing toliving comfort, as were the convertible bed -settee, the office -chair on which all the leg -joints were rubber -mounted, the portableoven and reversible windows for cleaningfrom inside.

There were many ideas which were byno means new to me. For instance, I had,several years ago, a device for recordingtelephone messages in my absence installedin my office. There was nothing wrongwith the machine except that callers, onhearing " Lord Donegall is out. Will youplease speak a message! " usually thought

that a gremlin had got into their telephoneand rang off in a panic.

There is nothing particularly new abouta thermostatic fire -alarm, either, althoughthe one exhibited was undoubtedly a verysimple device, relying on the fusing of apiece of metal at 16o deg.F. to establish anelectric -bell circuit.

Finally, in the Inventors' Section, thereis much to be said for a picnic -seat givingback support and folding -up into the size ofan umbrella.

There was a wool -winder transforming theskein into a ball, the strands being crossedover in such a manner that the ball couldnot unwind accidentally.

In the industrial field, I liked the strapand rollers for attaching to a suitcase, muchas has been done for many years with golf -club bags.

A revolving gear -box, claimed to increasemileage per gallon by 5o per cent., wasalso exhibited. It eliminates gear -changing,but whether it is an improvement on existingmethods of eliminating gear -changing inmotor cars is impossible to judge by lookingat it. It appeared no more bulky than anordinary gear -box.

Lastly, there is no doubt that were we allto install stoves such as the " M.I.," inventedand produced by an Anglo-Polish inventor inBournemouth, or the many ether stoves ofsomewhat similar design, we would getwarmer houses and save a good fifty per cent.of our fuel bill. But will we? I am afraidthat there is something about the old Englishopen fire that will cause inventors of moreefficient heating devices a headache for manyyears to come.

Making an AnemometerA Simple Device for Gauging the Speed of the Wind

N anemometer, or wind speed measurer,is easily made, but, at the same time,is a most fascinating piece of apparatus.

Four semi -circular cups form a kind ofhorizontal windmill which spins slowly or

Fig. a.-General view

of thecompleted

anemometer.

rapidly, according to the velocity of the wind.By means of a worm and pinion gear a pointermoves over a graduated scale, from which caneasily be found the speed of the wind inmiles per hour.

The cups are beaten out of circular piecesof sheet copper, exactly 4.71in. in diameter,and when finished must be exactly Sin. indiameter. If you do metal work this is asimple task ; if not, you can get them madequite cheaply.

The Four ArmsThese are made of Ain. diameter brass

rod, 115n. long. The vertical spindle con-sists of a suitable length of lin. diametermild steel rod. The boss, A, is 'lin. diameterand in. deep. Run a thread on the end of therod and tap the hole in the centre of the boss ;then tap four holes Lin. deep exactly atright angles' to take the threaded ends of thefour arms. Solder the cups firmly in positionas shown and screw the arm firmly into theboss, which is then tightened down on thespindle.

The worm wheel is fixed securely to thespindle by its set -screw (see Fig. I). Thebottom of the spindle is pointed and runs ina hollowed bearing block of steel, B. A collarand set -screw, C, keep the spindle in place.The pinion, which engages in the worm, has

56 teeth, and is fixed firmly by a set -screw toa spindle, D, which runs in bearings in thetwo brass strips, E E.

A dial of cardboard, graduated into 20 equalI 2parts and numbered up to

loois

too toois glued to the front strip. The front stripand half the dial is shown in Fig. 1.

The BoxThis is about 6in. long, Sin. deep and 4in.

high. It should be firmly screwed together.A sheet of glass forms the front, through whichthe dial is read. The bearing in the top of thebox is formed by screwing a piece of sheetbrass on and boring a hole just large enoughto allow the spindle to revolve freely. Thehole in the wood should be a little larger toallow perfect clearance. Fix the modelfirmly in an exposed position, as high aspossible, but so that it can be read easily.

If made exactly to these dimensions, 56revolutions of the cups-i.e., one revolutionof the pinion and pointer-equals of amile. Each division on the dial is thus - -

tooof a mile.

When the wind is blowing, watch thepointer and note carefully how many divisions

Fig. 2.-Side view of the worm and pinion.

it passes in one minute, or five minutes.

Suppose it moves from o to -1-10-: in one minute.

This means a speed of '!u miles in oneminute or six miles per hour. If the pointerdoes four complete revolutions in oneminute, this is V5 of a mile per minute, whichis 48 miles per hour.

Poffin says : "It's amazing haw Camm's harmonograph gets you after a time."


May, 1953 NEWNES PRACTICAL MECHANICS 331Magnet

To"waiverrelaycircuit

Escapement

Rotating member

Fig. 3.-An escapement actuator.

THE equipment in a radio -controlledmodel may be divided into threesections. First comes the receiver,

which may employ one or more valves. Therewill also be a propulsion motor (except insailing craft) and similar equipment connectedwith the actual powering of the model.Between receiver and propulsion and/orguiding motors and mechanisms comes thethird section of the equipment-the actuator.Many different types of actuator can be madeup, and the actual construction of suitableunits is not particularly difficult. In a sense,the actuator transforms the received impulseinto the desired action, which may be start-ing, stopping, reversing, or speed -control ofthe propulsion motor, or so on.

Actuator battery

To receiver

Fig. i.-Connections for receiver relay.

The types of actuator described here areprimarily intended for single -valve and othersingle -channel receivers. With such receivers,all desired operations in the model must becontrolled by the opening and closing of asingle circuit. Accordingly, in all but thevery simplest model, some type ofactuator is essential. Without an actuatormechanism, radio -control (with a singlechannel receiver) would have to confine itselfto one purpose only ; for example, the start-ing and stopping of a model boat's propul-1 sion motor. With an actuator there is almostno limit to the amount of control which maybe exercised. For example, the propulsionmotor could be started, stopped and reversed.It could also be made to run at half speedin either direction. In addition, steerage ofthe model, both when in motion forward orastern, could be effected. If desired, otheractions (such as the rotation of gun -turrets)could be provided for. It will, therefore, beseen that the realistic operation of a modelmakes an actuator mechanism essential.

Principles of ControlWith a single -channel receiver, the trans-

mitter is keyed so that a carrier -wave isradiated when desired. This causes theanode current in the receiver to fall, so thata relay is released. Such a relay is shownin Fig. I. It is of sensitive type, so that itwill operate with a current change of as little

Radio -controlledModel Actuators

Notes on Their Construction, and How They OperateBy F. G. RAYER

as .1 milliamp, and various relays are especi-ally produced for this purpose, and should beused.

When the transmitter is operated, thearmature is released, thereby completing thebattery circuit shown. If this circuit werewired directly to an electric motor, the motorwould run when the key at the transmitterwas depressed, and stop when the key wasreleased. This would only be sufficient in thevery simplest type of model.

A further circuit might be connected tothe lead " X," but this would, in most cases,serve no useful purpose. One circuit wouldhave to be switched on when the secondwas off, since the armature cannot be broughtto rest in a central position. As a result,

To nveycircuit

Electro magnet

Fig. 2.-A magnetic actuator.

the second circuit could not be used to operatea steering motor, or for any similar purpose.

Without an actuator the degree of con-trol is, therefore, the same as that whichwould be afforded by a single on/off orchange -over switch in the model.

How Actuators FunctionAll actuators change the simple making

and breaking of a circuit (as provided bythe relay) into more complex functions. Onemethod of doing this is shown in Fig. 2.

Here, an electro-magnet and pawl assemblycauses the rotation of a toothed wheel. Eachtime the magnet is energised, the wheel iscaused to rotate one tooth. Such an arrange-ment is quite straightforward to make up.The magnet needs to be fairly powerful, andthe pawl should move just sufficiently to takeone tooth each time the circuit is energised.

By keying the transmitter, the wheel maybe made to take up any one of eight posi-tions. If necessary, undesired positions maybe passed through almost instantly by key-ing the transmitter a number of times insuccession.

A different type of actuator is shown inFig. 3. Here, the wheel is constantly endea-vouring to rotate in the direction shown.Each time the magnet is energised, the wheelis allowed to rotate one tooth. This arrange-ment has a number of advantages in somecases. The magnet only acts as a release,

and the actual rotary force does not have tobe provided by it. As a result, heaviermechanisms may be operated.

In simple models, rotation is frequentlyprovided by a twisted skein of elastic. Asmall clockwork motor can also be used, orsome similar form of spring -driven mechan-ism. Where some other source of continuouspower exists, as with a steam -driven model,the toothed wheel may be driven through afriction clutch. It will then rotate each timethe transmitter is momentarily keyed.

Rotation of the axle upon which the wheelis fixed is made to fulfil some useful purpose.One means of accomplishing this is madeclear in Fig. 4. Here, a disc with projectingpin is fitted to the axle. This disc may bemade to take up any one of eight positions.With the steering arrangement shown, thiswould enable the rudder to be set in anyone of five positions, namely, straight ahead,half to port or starboard, and fully to portor starboard. Steerage of the model to thisextent would thus be possible.

A rotary switch with eight contacts isalso driven by the spindle. In the circuitshown, provision is made for forward andastern running, with " Off " positionsbetween each. It would also be possible towire up so that only one contact was unused,providing an " Off " position. Other con-tacts could then bring a resistance into cir-cuit for "Half Speed " running. Or, ifdesired, only one Astern " setting need beprovided.

In all cases switching of the circuit willtake place simultaneously with movement ofthe rudder. Eight different combinations maybe arranged for, and a good degree of con-trol will, therefore, be secured. A sequencesuch as the following would be possible.

Position a. Rudder straight, full speedahead.

Position 2. Rudder half to port, full speedahead.

Position 3. Rudder fully to port, fullspeed ahead.

Position 4. Rudder half to port, half speedahead.

Position S. Rudder straight, half speedastern.

Rotary switch

Slotted arm Spring

Fig. 4.-A reversing ani steering arrangement.


332

Position 6. Rudder half to starboard, halfspeed ahead.

Position 7. Rudder fully to starboard, fullspeed ahead.

Position 8. Rudder half to starboard, fullspeed ahead.

In each case undesired positions are passedthrough quickly by keying the transmittera number of times in succession. The modelmay thus be controlled to an extent permittedby the selection of any of the positions.

Many of the simpler actuators provide nointermediate position of the rudder, and eventhese are quite effective, since the model can

Double -pole change -over relay

meal6

VTo battery

Fig. 5. Motor reversing by means of a secondaryrelay.

be turned upon a new course in either direc-tion. If reversing were not desired, such anactuator could provide for full speed ahead,full speed to port, full speed to starboard,and " Motor Off " with rudder ahead. Thewheel on the actuator mechanism wouldrequire only four teeth. This would make themethod shown in Fig. 2 impossible, but thatshown in Fig. 3 would be equally suitable.

Toreceiverrelay)

16m.

Tomotor

NEWNES PRACTICAL MECHANICS

In Fig 4, reversing of the motor is obtainedby reversing the polarity of the supply. Thiscan only be accomplished by using a per-manent -magnet motor. If the motor has awound field, the polarity of the supply toeither field or armature should be reversed,to reverse the direction of rotation.

Secondary RelaysThe receiver relay may complete a circuit

which energises a secondary relay with addi-tional contacts. More complex circuits maythen be used. A reversing circuit is shownin Fig. 5. A double -pole change -over relayis used, and wired so that the motor isreversed.

This type of circuit has a number of appli-cations, usually in conjunction with an actua-tor such as has been described. The typeof relay used here is of about 200 to 500ohms resistance, is quite small, and normallyenergised by a 3 to 4.5 volt dry battery. Thesensitive type of relay such as used in thereceiver is not required. For example, thecontrolling circuit may be transferred fromone motor or actuator to a second, by thechange -over switching of the relay. Thischange can, in turn, cause yet other relaysand mechanisms to come under control.

Secondary relays must also be used whenthe current flowing is heavy, or of fairly highvoltage. The contacts of the receiver relayoperate a trifle slowly, and the contact pres-sure is small, especially when the model is atrange. Accordingly, the contacts will- notsatisfactorily make or break circuits passinga large current. They will, however, ablydeal with small currents, at low voltage, andcan, therefore, serve to control the energisingof a second relay. Such a relay might bepowered by a 3 or 4.5 volt battery, as men-tioned, and its contacts could deal withhigher voltages and currents. Such asecondary relay is essential in non -mobile

May, 1953

mechanisms where mains -voltage circuits areinterrupted.

Motor -driven SwitchingA small motor may be used to operate a

rudder, or other units, including switchesof suitable rotary type. Such switches becomealmost essential when very complex circuitsare necessary.

A method of operation is shown in Fig. 6,where a small motor drives a rotary switchthrough worm gearing. " Yaxley " rotaryswitches, such as used in radio receivers, aresuitable, provided the spring locator mechan-ism is removed.

When such a method of switching is

Multi -pole rotaryswitch

Wormgearing

To circuits

Shaft driven from motor

Fig. 6. -Multi -circuit switching.

adopted, there is almost no limit to the com-plexity of the circuits which may be used.The motor should, for preference, be rever-sible, as described. Such switches may bringinto service further sections of equipment,such as small motors to rotate turrets, latch-ing relays to switch on lights, and so on.

Back to First4. -Gravitational Force

indeed, is one of the thingsthat we are bound to accept, withoutexplanation, as a condition of our life

in the world. Through experiment andobservation we are able to say much withconfidence about the force -about the resultsof this tendency towards a centre of attraction.We speak of the " law of gravitation " asbeing that whereby " the attractive force ofbodies varies directly as their masses andinversely as the square of the_distance betweenthem.' But, assuming that Newton's won-derful guess is absolutely correct, this is astatement of what happens, and what we areimpotent to change. The explanation ofwhy each particle of matter tries to comecloser to every other particle still eludes us ;we only know that it does.

The Problem : A ball is thrown verticallyupwards at a speed of 128ft. per second.Find where it is after 5 seconds, and the'total distance it has actually travelled. If itfalls past the point of projection into a wellnoft. deep, find when it strikes the bottom.

The Comment : We work on the assumptionthat the accelerating effect of gravity -weshall denote this by g -is 32ft. per second;it is a little less than this up the mountain,a little more than this down the mine. Ifwe denote the number of seconds by t, thengt is the acceleration due to gravity ; and / gtwill be the average speed. The distancetravelled, therefore, is igt2.

If now we denote an initial upwardacceleration as it, we are able to expressthese three equations:

PrinciplesBy W. J. WESTON

I. The velocity at any point is: v=u-gtII. The space travelled is : s=-ut gt'.

III. And, combining I and II: v2=u2- 2gs.Since, therefore, at the highest point -

which we denote as h -v =o, then u2=2gs.The Answer . s=128 x 5 - (32) x 25 =

24oft. up.128

But the greatest height is reached in -gt

seconds, i.e., t is 4 seconds.After 5 seconds, therefore, the ball has

been moving downwards for r second, i.e.,over 16ft. The total distance, therefore, is240+16 up +16 down=272ft.

Since the ball falls below the point ofprojection, s 'becomes negative. So :

-120=128 X t -160i.e. 160-128t =120

15i.e. t2- 8t =

2

(Add i6 to each side)

(t - =t =8.82

V23.50 = 4.82

seconds.

472

The Problem : If a stone falls past a window8ft. high in half a second, find the heightfrom which the stone fell.

The Comment : This involves the calculationof the velocity of the stone when it reachedthe window : that velocity would operateduring the passage of the window over

second. We need to calculate also the space

through which the stone, starting from rest,would travel in / second.

As regards the first calculation, since thepositive direction is now downwards, theequation of motion is : v2= u2+2gh,or since u=o (the stone starting from rest),v2=2gh.

The Answer: Space through which a bodystarting from rest falls in / second =1 gt2=(16 x )ft. =oft.

The velocity of the stone when it reachesthe window is 4ft. in the / second, i.e., 8ft.per second.

And, since v2=2gh,82=2 X 32h=64h.

That is, 8=8N/h orThe height above the window is, therefore,

The Problem : A ball is propelled verticallywith a velocity of 56ft. per second. At whatheight is it moving at 4oft. per second ; andwhat is the time between the instants whenit is at this height ?

The Comment : 'This is merely a variantof the first problem studied, and we applythe equations with the necessary modifications.

The Answer : The equation of motionwhere u is the initial upward acceleration andv the velocity at the time, and h is the height infeet reached is v2=u2-2gs.

Or 40 X 40=-56 X 56-2 X 32Si.e., 64s =562 -=40926=x(5i66+ 4o) (56 - 40)

s=24ft.An upward acceleration of 4oft. per second

is wholly lost in

-40 seconds, i.e., in I seconds.grt

And since a downward acceleration of 4oft.per second is gained in the same time, thetotal time required is : 21 seconds.



Our artist's impression of the SchimdtMount Palomar.

telescop2

THE second departure is due to Maksutov9, 10, 11. Dr. Linfoot discussed this in

" The Observatory " and referred to theoptical system as the Meniscus -Schmidt.The arrangement is seen in Fig. 12. Theaspheric Schmidt corrector plate is replacedat focal ratios of f/3 and apertures up to2 or 3ft. by a meniscus lens, the sphericalsurfaces of which are nearly concentric withthe mirror surface. The primary colourerror of the meniscus is corrected by aspherical interface which takes the form ofa doublet with its two glasses of differentdispersions and the same mean refractiveindex. The off -axis colour errors introducedby the spherical interface though notnegligible are harmlessly small.

Folded and Solid Schmidt CamerasFinally, two adaptations of the classical

Schmidt are not without interest. The solidSchmidt camera, Fig. 13, and thefolded Schmidt camera, Fig. 14, due to

Spherical mirror

Fig. 12. Maksutov, or Meniscus -Schmidttelescope.

Hendrix, which places the image surface ina readily accessible position.

In considering the folded Schmidtcamera it is convenient to draw attention tothe optical system used in modern projectiontelevision. Fig 15 shows the system used byMullardla. In contra -distinction to thetelescope aspect we have considered through-out : the television application places theimage on the image surface as its initialstep in the light path ; and the imagesurface is the fluorescent screen of thecathode-ray tube, AB (Fig. 15). Considerpoint A, a single picture element. Lightradiated forward from picture element A

at

The Work of Bernhardt Schmidt and its Relation toTelescopy and Other Sciences

By FRANK W. COUSINS, A.M.I.E.E., F.R.A.S.

(Concluded from page 292, April issue)reaches the spherical mirror, D,which reflects it as a convergentbeam on to the flat mirror, E, at45 deg. to the axis of the cathode-ray tube. The light from E passesthrough the Schmidt correctorplate, F, on to a second mirror, G,and finally on to the screen, S, atK. This provides an enlargedimage of the picture element, A,at K, and is applicable to all theother picture elements.

One other use of the Schmidtsystem outside of astronomy is that of itspart in roentgenology. It has been stated byBrockman13 that the Schmidt system isused to detect cancers of the stomach.Cancer, like tuberculosis, can be detected byX-ray methods, but the examination ishindered by the very much lower trans-missivity of the gastro-intestinal regions toX-rays as compared with the transmissivityof the chest, and this means that thefluroscopic image is faint. To avoid long

Image_surface

Fig. t3.-Solid Schmidt.

exposure and over -dosage of the patientwith X-rays a fast lens system is essential.Here Schmidt's system lends itself to a reallyfast camera design, and this, though in theearly stages of development, may makepossible mass -radiography of the stomach asnow done for the chest in the war ontuberculosis.

Newton Telescope at HurstmonceuxIn closing this appraisal of Schmidt's work

it is gratifying to report that the Isaac

Fig. 15.-Schmidt sys-tem for television.Compare with Fig. 14.

Newton telescope14 which will be erectedat Hurstmonceux in Sussex will be of theSchmidt construction and the largest, in theworld. The main mirror is to be 98in. dia.;

xN-Avr\

Imagesurface

Mirror

Correctorplate

Fig. r4.-Folded Schmidt.

with a corrector plate of 85in. dia., and thephotographic plates will be i4in. x 14in.What will such great instruments tell us ofour universe ? The answer to such a questionis not possible. We can read again, inhumility, the words of Prof. Grant quotedin the preamble to this article, and note thatthe telescope has ever been an iconoclast inits treatment of the contemporary view-

A close-up veiw of the eyepiece end of the SchmidtCassegrain telescope at St. Andrews University.

reducing the speculation of many philosophersto ashes. The future may well beiconoclastic for many current ideas; theenigma of the universe is far from solved.

REFERENCES9. " Journal of Optical Soc. America " 34, May, 1944,

p. 27o. (New Catadioptric Meruscus System.)D. D. Maksutov.

so. " Scientific American," Oct., 1944.11. " The Observatory " 66, p. 239.12. " Mullard Outlook," Vol 2, No. 4, Jan., 1952.13. " Journal British Astronomical Association," vol.

14. `?.TFrp.ne5s6kogress of Science," April, 195o, p. 8 ;also " Optical Instruments, Proceeding of,'' LondonConference, 595o.



camera, using single plates which are longenough to accommodate two views, side byside, each measuring 3fin. by 31in. Thismeans that the optical centres of the lensesmust be 34in. apart, which they nearlyalways are. In the stereoscope two lensesare required, one for each eye. Now, asthe human eyes are approximately zlin.

pEOPLE who have lost the sight of oneeye can never see objects in the roundor in relief, and are only able to judge

distances by moving the head from side toside. The normal sighted person, using botheyes, can judge distance without movingthe head. The reason why this is so andwhy all objects in nature appear in relief ;why they have depth as well as breadth andheight is because the images formed on theretinas of the two eyes are not exactly thesame ; the right eye sees the subject from adifferent viewpoint from the left. This is

on a table a bottleand a candle ; let the candle be the neareralmost in line with the bottle. Now closeand then open one eye, then the other; dothis repeatedly in rapid succession and it willappear that the candle keeps moving, firstto one side of the bottle and then to theother. This is stereoscopic vision.

If we substitute for the eyes two photo-graphic lenses attached to a double -widthcamera, fitted with sensitised plates or films,we can photograph exactly what the two eyeshave seen. The two resulting pictures,taken by different lenses from slightlydifferent positions, may appear to be alike,but if the subject photographed was a simpleone, like the candle and the bottle, thencareful examination and, perhaps, measure-ment, will show that the candle in onepicture is a little nearer to the bottle than in

111

ST EOSCOPESInstruments Suitable for Viewing Two -lensed Camera Slides and

Single-lens Camera Stereosthe other. This is stereoscopic photography,the result of which is a pair of photographicprints, mounted side by side, which, in orderto be viewed stereoscopically, must be lookedat through a stereoscope.

Obviously, the two prints must be mountedin correct order. If the left-hand photo-graph were placed on the right side of themount and the right-hand on the left, thenthe more distant object would appear in

Fig. 1.-Showing

By E. W. TWINING

possessing all the solidity and relief of theoriginal subject.

Stereoscope for Two -lensed CameraPicturesIt is proposed to give drawings of two

stereoscopes, dealing with the larger one first.This is of the size and type which is

required for viewing pairs of pictures takenwith a double -lensed, orthodox, stereoscopic

how the lenses bend the light rays.

front of the other and the perspective andsolidity of the objects would be reversedand all wrong.

The stereoscope compels the left eye tosee the left-hand picture and the right eyethe right-hand. The two views are thensuperimposed by the optic nerves, producing,in the brain, the effect of one picture

OPTICAL CENTRE LINE

Fig. 3.-Side and front end elevations of alarge stereoscope.


May, 1953

Fig. 2.-Cutting up the reading glass.

apart and as they have to view picturesspaced at 34in. centres the lenses must, tosome extent, act as prisms and possess thefaculty of bending the light rays from thepictures and at the same time magnifyingthe images. In this type of stereoscope,therefore, ordinary circular lenses are notusually used, but they are shaped as shownin Fig. 5, which figure also shows how thepicture images are caused to converge to theeyes. Such a pair of lenses can be made bysimply cutting into halves, on its centre -line,an ordinary reading -glass lens of about 8in.focus and zlin. dia. With the furtherremoval of other thin portions, near the edge,two square prismatic lenses, as drawn inFig. 2, are the result. The stippied portionsare the parts to be removed.

The cutting of such a lens as this is asomewhat delicate operation, unless one is a


MOUNTFr:-.1 PICTURE -4F.-- et.

I..----

CENTRES OF PICTURES

Fig. 6.- Pair of 38in. >: 2 lin. prints mounted.

Using the Single -Lens CameraI have mentioned the two -lensed stereo-

scopic camera for the .taking of pictures, andwhen it is necessary, or advisable to makeboth exposures simultaneously, the double -lensed instrument is essential, but for ordinarylandscape work a quarter -plate single-lenscamera can quite well be used, mountedupon a cross -sliding head to the tripod stand.In this case the two views are taken oneafter the other, first with the camera on theleft and then on the right. In some respects,and wherever it is possible, this method has

924'

Fig. 4.-Plan view of the stereoscope.

skilled glass -cutter, and it is one whichshould be done with a glazier's diamond inpreference to the ordinary glass -cutter'swheels. It is recommended that all of thecuts be made with the diamond before anyone fracture is completed ; then, obviously,the first cut to be parted is the main oneacross the centre of the lens. It might beadvisable to get a glass -cutter to do the job.

The two lenses are mounted as shown inFigs. 3 and 4, which drawings give all thedetails of the construction of the stereoscope.Both the lens panel and the picture stage,together with a handle underneath, are madeto fold, for convenience in storing. As maybe seen, the stage is made to slide, for adjust-ing the focus to suit different sights. Loose-ness in sliding is prevented by a strip ofsprint -brass, which should, at its middle,press downwards on the main bar, orbaseboard.

Although ordinary grained wood is shownin the drawings, plywood will be most suit-able for all the principal parts and only afew bits of straight -grained material will becalled for. To hold the lenses in the lenspanel, either wood veneer or cardboard maybe used ; the former being best for appear-ance, if the whole instrument is polished orvarnished natural colour.

advantages, because both pictures are takenwith the same lens and with exactly the samestop value. When two lenses are fitted ona stereo -camera they have to be perfectlymatched: for colour in the glass, for equiva-lent foci, for diaphragm apertures and formounting on the front of the camera, factors,

4>t" INSIDE

2-vf -CEtITRIS -.4

..4OUTSIDE ---+r-0- OPE PI

DETAIL Of FABRIC H 1146E9

( INLARGED)

335

any one of which can affect the resultsenormously.

The second scheme for making stereo-scopic pictures and a stereoscope for view-ing them may be welcomed by thousands ofpeople who own and use ordinary box -typecameras, or any hand -camera which, havinga flat underside, will stand upon a flat sur-face. There are quite a number of moderncameras of this type on the market, rangingin price from £50 or more down to a littleover £t, all taking pictures either 3,tin. byzlin., or zlin. square, and all suitable foruse in the manner I propos:, to describe.There are others which fold up, with bellowsextensions, and these also can be used,though the trip ad top may have to be madea little differently to suit the bottom of thecamera.

Stereoscope for Standard NegativesFirst with regard to the steroscope:

Fig. 5 shows a somewhat simply con-structed viewing instrument. Fig. 6shows the correct measurements andarrangement for a cardboard mount carryinga pair of stereo prints, either 3* x zlin. orzlin. square, the latter being, of course,taken by one of the many cameras whichare made to produce square pictures. Thesemounted photographs are sometimes termed" stereoscopic slides," and, for want of abetter title, I shall use the word, althoughthey do not in any sense slide. The doubledot -and -dash lines across Fig. 6 indicatethe positions which the zlin. square pic-tures are to occupy. Any titles to the pic-tures can be written underneath, and shouldappear under one picture only, so as to beread by one eye. With 31in. pictures, titlesmay be put on the backs of the mounts orin fine writing at top or bottom.

The stereoscope is made of cardboard ;the yellow -brown type which is known as" strawboard." It is cheap and is readilyobtainable. The thickness should be notless than 5/56in. All the pieces shown anddimensioned in the drawing, Fig. 5, shouldbe cut out with a pointed knife and steelstraight -edge, cutting being done preferablyon glass. Then all the parts should be givena good soaking coat of strong size and allowedto dry thoroughly.

The bottom of the stereoscope is made toform a box which, when closed, should holdfrom 55 to zo slides, according to theirdegree of flatness. If prints are pasted onboth sides of a mount, back to back, the carddoes not tend to curl, and the slides shouldremain flat. In this way thirty or forty viewscan be got into the box of the stereoscope.

The folding parts of the instrument arejoined to each other by hinges formed bystrips of fabric, arranged as in the enlargedsketches, at the left-hand lower corner of

-a PICTURE TO TITRE Of LENSES

r I '

Nor

i//

CLOSED [-- IV OUTSIDE -

............Fig. 5.-A folding stereoscope for 31in. by 2Iin. pictures.



LENS

PLAN OF FROM EDGEOr BASE BOARS.

Fig. 7.-Using a box camera for taking stereo-scopic pictures.

Fig. 5. These strips are not allowed to stickto the edges of the card but only to theinner and outer faces, so that the hingedpiece of card has a full 18o deg. of move-ment.

I suggest that the stereoscope be coveredentirely with good quality bookbinders'cloth of any approved colour, preferably darkgreen or black, and if this idea is adopted,bits of the same cloth can be used for thehinges, such hinges being put on before thecloth covering.

The lenses, since these will be approxi-mately the same distances apart as the cen-tres of the pictures, do not need to be pris-matic, and two exactly similar lenses, eitherplano,convex or double convex, will berequired. They should each have a focusof 4in. and diameter kin. If they are piano -convex, insert them in the spectacle platewith the convexed sides towards the pic-tures. They need not be cemented or stuckin any way, but. will be held in the " plate"by two rings of card, glued on either side ofthe strawboard. The remaining details ofthe stereoscope will be obvious from thedrawing.

The TripodThe camera arrangement for taking the

pictures involves the use of a folding tripodof the size usual with quarter -plate fieldcameras, having folding and sliding legs anda wooden top. There are tubular brass -legged tripods, with small metal tops, butalthough they are somewhat smaller whenshut up and a trifle more convenient forcarrying, they are too large to go into thepocket ; and, what is of greatest importance,are too subject to vibration, even from lightwind pressure, to be of any use in makingtime exposures in stereoscopic work. I haveone wooden tripod which folds and slides,made of ash, which weighs, with its top,only and it is the upper part of thiswhich is drawn in Figs. 7 and 8. I stronglyrecommend the interested reader to obtainone of these.

The PlatformThe most simple arrangement for a fitting

to go on the tripod top is a rectangularwooden platform with a ledge around threesides of it, as shown in Fig. 7. On thisthe camera is placed, first on one side and thefirst exposure made, and then on the otherside for the second exposure. No dimen-sions for the platform are given, the reasonbeing that since the lens must move, between

the two camera positions, a distance of31in., the cross length of the platformbetween the side ledges will depend upon thewidth of the camera. Cameras vary greatlyin width, as well as in other dimensions, andthe reader must make the platform to suithis own particular camera. Measure thewidth of the camera at the bottom, add theresult to and the sum of the two willbe the length for the platform between theledges. In using the platform the cameramust be pressed up into the angles formedby the front as well as the side ledges, thusthe camera will be kept square and point inthe same direction for both exposures.

Varying Lens SeparationAnother, more elaborate scheme is drawn

in Fig. 8, where provision is made for vary-ing the amount of movement of the camera,in order to increase the separation of thelens positions from the standard 31 -in. to4 -1 -in. with several intermediate measure-ments. The purpose of increasing is some-times important and this ability to increaseis where the single camera scores over thefull, double -lensed, type, where the lensesare fixed. If photographing a distant land-scape, with mountain scenery, withoutforeground and no objects nearer than, say,sooft., a separation of 3iin. would not besufficient to give the necessary amount ofstereoscopic relief and solidity. In such acase 41in. would be only just enough to yielda realisable amount. In taking pictures forthe stereoscope it is the variety of distancesof foreground objects which are all-important. The following may be lookedupon as a safe guide-A: 6ft. to zoft.,B: loft. to soft., 3kin.; C: soft. and beyond,41in. The lowest figure, 6ft., is the shortestdistance that can be allowed between thenearest part of the foreground and thecamera; not because it would be out of focus-that can be corrected by stopping down-but because, were it nearer, than 6ft. there

STOPSC B A

r-64-77

w:314-cENTRES A I

CENTRES 84,1c rims

it

ends are inwards, the carriage is stopped at3kin. separation, while if the turnbuttonsare placed parallel with the ends of the plat-form and with neither end inwards, the fulltravel is available for 41 -in. separation. Otherintermediate travels are possible by havingthe buttons differently placed at oppositeends. The plan view of one end of theplatform, with a bit of the camera cross -slideshowing, is added at the top of Fig. 8. Theplatform and the main part of the slideshould be made of plywood, the latter of5 mm. and the former of 9 mm. thickness,that is to say 3/16in. and kin. The rebatingof this can be such that two of the plys areleft the full width of the platform and threeplys removed to form the rebate. The finishcan be shellac varnish, leaving the woodnatural colour or, on top of the shellac, acoat of eggshell -black lacquer can be given.

Close-up StereosShould the reader wish to make stereo-

scopic views of really close-up objects andcan put magnifiers over his camera lens, hecan make slides of such things as still life,fruit and flowers and models, etc. In thatcase the camera movement will require tobe less than 3/in.; probably much less, say,2 to zlin. or according to the size anddistance of the object. Whatever the cameramovement is, be it tin. or 4zin., flowers ordistant landscape, the mounting of the printswill be the same, as given in Fig. 6.

I think it is perhaps advisable to remindthe reader, before he sets out to do stereo-scopic work with his one and only handcamera, that only " still " pictures can hetaken. There can be no snapping of movingobjects; even in pure landscapes there mustbe no wind-blown tree movement, but theuse of the instantaneous shutter can be

r

PLAN OF ROTARY /STOP PIECE /'

BASEBOARD

:ROSS SLIDE

Fig 8.-Tripod top withwould be difficulty in seeing that particularbit of foreground stereoscopically; when thetwo pictures are mounted the eyes would notbe able to superimpose the two imagesthough all the rest of the picture may be inproper relief.

Fig. 8 shows the platform, on the tripodtop, with rebates, on each of the long edges,to receive a sliding carriage or cross slide,which carriage is made so that the camerafits snugly into it. The platform is madelonger than is required for 3iin. separationand, at each end, it is fitted with a turn -button having unequal ends. When the longerends are both turned inwards to A, the crosstravel of the slide is 3in.; when the shorter

cross -sliding camera carrier.

dropped, in most cases of doubtful light,with advantage. The best way is to stopright down, get perfectly sharp detail inforeground and distance and make " time"exposures, though, of course, the timing ofboth exposures must be exactly the same.With the smallest stop and long exposuresthere is no difficulty in getting the timingexact. Of course all this depends upon thecamera, the lens, the type of shutter fittedand the speed of the film being used. Withan expensive outfit having a lens working ata big full aperture and depth of focus andwith high-speed film, time exposures wouldbe rarely necessary; only perhaps in buildinginteriors.



The Manufacture of PinsWith a Description of the Types of Machine Used

AQUANTITY of the wire produced inmost countries goes into the manufac-ture" of safety -pins, particularly those

embodying a sheath of metal to act as areceptacle for and protection of the point.In making these, the preliminary stage com-prises straightening, cutting off and pointingthe wires. This cannot be done exactly aswith needles. In the first place, it is vitalthat the cut-off wires should be of identicallength, or it would be impracticable to per-form the later operations. The necessaryaccuracy cannot be secured when the grindingof the points is done by means of a wheelrunning away from the point. The grindingmust be done towards the point, and inFigs. r and z the principle of the machineused is indicated.

The wire supplied in the normal coils isplaced on a swift to the rear of the pointingmachine, and pulled forward by a revolvingstraightener consisting of a number of pegs ina revolving frame. The actual drawingthrough of the wire is carried out by twofeed rolls actuated by a double -crank feedingmechanism. Each stroke of either crankcarries forward sufficient wire to form onepin. This pin is then cut off.

The DrumTo the front of the machine is a barrel or

drum which rotates on a horizontal axis,

Rubber drum

Poo t ing mill

roothed drum

Stec,'mill

Carborundum mill

Fig. 2.-Details of the drum and thesteel mill.

and as the wire comes forward it protrudesover this. The drum is composed of threeindividual discs, two of them, those external,have teeth round their peripheries. Theseteeth are generally inserted so as to makereplacement easier in the event of damage.The middle disc is rubber -covered and causedto revolve by interior gears at twice the rateof the toothed sections, but in the samedirection.

By H. SANDERS

Precisely as the wire is severed from thestock, a finger descends and forces the wiresquarely into the gaps of the drum teeth.The teeth thus engage the wire and carry itforward until it is forced to pass under, asaddle formed like the drum periphery. Thewire is held square by the teeth, and simul-taneously it is rolled overagainst the saddle by the ,

rubber drum. Behind thedrum is a plate against whichthe wires butt, and thisensures the dead accuracy oftheir frontal protrusion.

In front of and alongsidethe drum on the right is aswiftly revolving steel mill,having teeth of file type. Thisis concave, as shown in Fig.z, and is located in such away in relation to the drumthat the requisite curved taperis acquired by the pin point.The mill, revolves in the direction of thepoint, and the grindings are removed bymeans of an exhauster. The diameter of themill is approximately 2-2.5in., but it revolvesat 5,000 r.p.m. and rubs rather than cutsaway the metal. The file teeth are speedilyworn down, after which the mill functions

Coil of caP strip

Forming pun&

Ceiling spit(fixed)

Formoo bed

Driving peg

Headfinishingtool

Fig. 5.-Showing how the horizontally movingfingers transport the wire to the head -forming

tools.

PressesBlanking Drawing -through Capping

lank

From these pointing mills the wires arepassed to a hopper, whence they are periodi-cally removed.

There is another method in which the pinis wholly made in one single machine. Figs. 3and 4 show the principle of one suchmachine, the invention of B. L. Goodman.In this machine the strip is fed by a coupleof rolls across a drum, which slightly oils the

Cut-offFeed rolls

Revolving straightener

Fig. 1.-Method of grinding the points of he pins.

underside of the strip. It then passes be-tween 'two press tools, which form a blank, asshown in Fig. 3. This blank is then carriedthrough to another press, in which a blunt -nosed punch drives the blank through a holein the die, thus making the cap in oneoperation. Under the die are two fingers,

Head forming toolsbehind here

in the same way as a circular friction sawused for cutting up steel girders. In short,its high speed causes it to burn rather thancut its way through. Eventually, when theserrations have worn down to nothing, andthe mill has acquired a high polish, it isremoved and re -toothed. The friction ofthe mill brings the wire to a red heat, but assafety -pins do not have to withstand stresseslikely to be serious, this heating up of thewire need not be taken into account.

The Steel MillFrom the steel mill the wire passes to a

similar carborundum wheel situated as shownin Fig. 2. Though this mill may be at anangle to the drum, as shown, it is sometimesplaced in a frame parallel with the drum face,and reciprocated in such a way as to followthe form of the point.' Lastly, a third millbarely makes contact with the point at arather obtuse angle, thus giving it a setcorresponding to that of an edge tooth.

A steel mill is used in advance of thecarborundum mill because otherwise thelatter would be too quickly destroyed byhaving to grind the square point. This thesteel mill is much better fitted to do.

Coilingspindle Spit

Transterer

Presser

Spring fingers

Hopper ofwires

Picking up Par

Figs. 3 and 4.-Theprinciple of the pin -mak-ing machine invented by

B. L. Goodman.which are rocked forward as soon as theyreceive the cap and force it through a slitin the bolster. The cap is then transportedto a capping press, with its open end to thefront, awaiting the shaped wire. Care mustbe taken to prevent the drawing -through toolsfrom scratching the metal, these scratchesbeing due to the presence of a slight fash orburr on the upper edge of the blank, which,if not perceived, scores every cap and quicklygrows bigger, since they become glass -hardand can only be eliminated by hand rubbing.

Head -forming ToolsThe pointed wires are fed from a hopper

on the right-hand side of the machine, andare picked out singly by a rising bar, whoseupper edge is nicked with a vee, so that eachtime it lifts it takes a wire. A light pressermaintains the wire in the vee until horizon-tally moving spring fingers arrive and seizeit. These transport the wire to the head -forming tools, as in Fig. 5. The stub endof the shank is held between punch andbed. The middle of the wire is supportedby a stationary spit emerging from the endof a coiling spindle. This spindle also hasan out -of -centre driving peg which bears



against the other side of the wire and coilsit about the peg as the spindle revolves. Thespindle revolves i times so as to make thespring loop, while simultaneously the head -finishing tool functions and finishes theshaping of the J -end to be fixed in the cap.

Thus, the wire shank is now finished, andis released by the reversal of the coilingspindle for a quarter of a revolution. Thisliberates the central spit from the grip ofthe wire. Axial withdrawal of the spitthen occurs, and the coiling spindle drawsback to permit the transfer fingers to seizethe pin. Immediately the fingers seize, thehead -shaping tools let go the other extremityof the wire.

Other processes following include scour-ing, cleaning, plating and the like. It isprobable that the machine described aboveis no longer obtainable, but the patent can,

Fig. 6-Safety-pin coiling machine.

no doubt, be consulted. It serves as anindication of the ingenuity devoted to themanufacture of these useful articles.

Safety -pinsIn Fig. 6 is shown a different type of

machine, made by Edward White, ofRedditch. In this machine the wires arecoiled into the form of a safety pin. Themethod is to begin with wires alreadypointed on the lines previously indicated,and then to pass them through this machine.The caps are then soldered on, being madewith a hand press, the result being thefinished safety -pin.

There are, naturally, other forms ofsafety -pin in addition to those with a metalsheath or cap. One such pin is composedwholly of wire, having a coiled loop at eachend, and is manufactured in machinesbased on similar principles to those alreadydescribed. In these instances, the pointedwire is removed from the hopper, and oneend inserted in a press having a vee notchin the anvil, with a corresponding toolabove. The coming down of the presspresses out the wire end into a spoon shapewhose recess finally serves as a sheath forthe pointed end of the pin when closed.

Another outlet for wire is the hairpin,though this, of course, is less popular thanit was some forty years or more ago. Fig. 7shows White's automatic hairpin -makingmachine, which automatically produceshairpins complete, straight from the coilof wire, either plain or crimped. Theactual work of bending the pins is easy,being done by simply tugging a length ofwire by the middle between two stops, thusfolding the two ends together.

The principle of this machine is that the

Fig. 7.-White's automaticmachine.

hairpin -making

wire is coiled, placed on a swift, and pulledthrough a number of pegs that serve tostraighten it. The wire when straight isprojected for cutting off by a cam -actuatedtool. The wires are then rolled forwardon their own axes and travel across the facesof two mills, running at high speed, andprovided with file teeth. The angle ofpresentation ensures elimination of theburr or fash due to the cutting tools, andforms a blunt, cone -shaped point, which isall that is necessary. The wires then moveforward and fall on to guides where thebend is made. If crimps are desired,crimping tools then seize the wire and carryout their work.

ADJUSTABLE WINGRESEARCH AIRCRAFT

THE Short S.B./5-the "adjustablewing " research aircraft which first flew

last December-has now completed a con-siderable number of flights. The researchprogramme for the aircraft is well underway and further details about the S.B./5can now be released.

Its main task is to investigate problemswhich arise in the handling of swept -backwing high-speed aircraft. Difficulties areencountered in maintaining full and imme-diate control of swept -wing aircraft at lowspeeds owing to a tendency for the airflowto break away or " spill " in the region ofthe wing tips, thus causing loss of stabilityand a tendency for the controls to appearnot to respond at critical speeds such astaking off or landing.

The results of the flying investigationscarried out by the S.B./5 will be made avail-able to the whole of the aircraft industryfor the benefit of British aviation.

Adjustable Sweep -backThe S.B./5 was designed so that varying

degrees of sweep -back can be applied to thewings. The tail plane can also be positionedeither at the extreme top of the fin or belowthe rear part of the fuselage and its angleof incidence is variable.

A programme of test flying to investigatethe low -speed handling characteristics of allthe combinations available is to be carriedout.

The varying degrees of wing sweep -backangle are achieved by fitting alternative com-ponents and four configurations can betested. These are :

Tail plane at maximum negativeincidence position

43. 6°47.4"

Side and front elevations andplan of the Short S.B.I5

angle between so deg. above or so deg.below the horizontal.

All -metal WingsFull span leading edge flaps are fitted and

the wings are all metal structure with ply-wood covering the leading and trailing edges.

1.- ICC- 3" -.1

Dependent upon ,

U/G positron --4-14-65Max10'--108"min

50°0Contiguration 35'-227" The undercarriage is a60 - - 36-6-02` non -retractable main- and690

" 25-11-72" nose -wheel unit. The atti-tude of the undercarriage

can be changed to enable each configurationto be tested at various C.G. positions.

5o deg. High tail unit.6o deg. Low tail unit.6o deg. High tail unit.69 deg. High tail unit.

The angle of incidence of the tail planecan be varied in flight and set to any desired

Single Jet EngineThe S.B./5 is powered by a single Rolls-

Royce Derwent jet engine which is posi-tioned well aft of the pilot. The pilot'scockpit incorporates an ejector seat.

The aircraft is fitted with anti -spin andbraking parachutes.

Pilot in all the test flying has been TomBrooke -Smith, chief test pilot to ShortBrothers & Harland Ltd., of Belfast, manu-facturers and designers of the S.B./5. Sofar all flying has been carried out with asweep -back of So deg.



111110111111111111111111111111111111111111111111.111

All Items Carriage Paid.MAINS OPERATED BELL -At last a

door bell without Batteries orTransformers. Operates direct fromMains Supply. 3in. Magneto typeBell by famous manufacturer completelyself contained. Equally suitable forburglar alarms, etc. 200-250 A.C.Supply only. Unrepeatable at 6/6.

HIGH PRESSURE REDUCINGVALVE. -Complete with 0-3,000 lbs.per sq. inch pressure gauge. Suitablefor Compressors, Cylinders of Gas, etc.Brand new, 8/6.

TOGGLE SWITCH. Single -hole panelmounting, 250 v. 2 amp. Single -polechange -over or on/off. Brand New,6 for 5/-.

DIMMER SWITCH. 96 ohms resistance.On/off position. 6 for 5/-.

EX-R.A.F.SIGNALLINGLAMP. -Triggeraction control. Al-ignment Sights asillustration. Com-plete with 6ft.Cable and 2 pinplug. Easily con-verted to Car SpotLamp. Price excluding Bulb 10/6.BRAIDED RUBBER TUBING. 3/I6in.

bore x iin. o.d., suitable for gas, air lines,etc. Limited quantity, 10ft. lengths, 4/,

ACCUMULATORCUT OUT. 24v.60 amp. Ex-R.A.F.,originally costover E6 each,.suitable for batterycharging, e t c .Limited quantityat 15/- each.

EX-R.A.F. GLIDE PATH RADIOS.R.I 124 comprises 6 valves-3/9D2's(VR.I06), 15D2 (VR107), 8D2 (VR108),4D1 (VR09), N.F. 7 m/cs, 6 switchedfrequencies. 30.5-40 m/cs plus a host ofvalve -holders, screening cams, 2 trans-formers, 33 fixed condensers, 30 trimmercondensers, 35 resistors, 6 coils, 5 waferrotary switch, potentiometers, etc.,unrepeatable at 30/-, carriage paid,new and boxed.

ALTIMETER. 0-3,500ft. Aneroid instru-ment suitable for conversion to baro-meters. 8/6.

AIR POSITION INDICATOR. Con-taining a wealth of gears, drives andshafts, 3 infinitely variable gears, lamp -holders, repeater motors. Veedercounters, has been used by manyUniversities as a basis of a calculatingmachine. (As illustrated.) E2/7/6.

SELF -PRIMING PUMP. Self-containedmotor 12 v. D.C., immersed type pump.Flange mounting suitable for bilge pump,caravans, etc. (as illustrated), 30/- each.

ANTI -VIBRATION MOUNTINGS. 3complete sets of 4, suitable for radiochassis, compressors, etc., 8/- per doz.

EAR PIECES. Single head set type. Lowimpedance, suitable for telephone sets,etc., 2/3 each.

TERMS -CASH WITH ORDER.NO C.O.D.

SHERMAN'SSUPPLY COMPANY P.M.126, KENSAL ROAD, LONDON W-10

11111111.1111.11.1111111MIINNIIM

e skill at yourfinger S *

You get immense satisfaction from X-acto, accuratecutting is so easy. You select one of the interchange-

able X-acto blades to suit the work in hand; quicklylock it to the appropriate handle and you have a firm,rigid knife with the sharpest blade you can buy.

There is an X-acto blade for every cutting job.See the full series at your X-acto Stockists (who willalso show you the range of X-acto knives and tool kits)or write for illustrated folder.

Blades from 2/6 for five. Knives from 3/6 each.Tool kits from 23/- to 84/-*

TRIX Ltd., Dept. A, rr Old Burlington Street, London, W.i

Gag

WILCO ELECTRONICSThe following are just a few items in ourstocks. Send 6d. in stamps for compre-hensive list giving full details of Poten-tiometers, Condensers, Resistors, Tele-phone Key Switches, Rectifiers, etc.

PHOTOGRAPHICENLARGER TIMER

A first-class clockwork timer,constructed from an ex -Govt.unit giving to 16 -second ex-posures with each winding.Complete with Foot Switch,Calibrated Dial, Focusing Switch.Ready for connection to themains, at the very low price of50/-, plus 2/6 post and packing.

PORTABLE P.A. SPEAKER CASEfor 12in. Speaker.-Rexine covered, 191n.x 171n. x 13in. ; removable back, carryinghandle, keys, provision for cable, metal -protected corners. Brand NEW. Specialvalue, 70/-, carriage and packing 10/,POWER AMPLIFIERS. -50 watt " Tan-noy " rack mounting, less valves, only58/10/- to clear. Carriage 7/8. VoltageAmplifiers, 28. The transformers andchokes are guaranteed O.K., but some smallcomponents may require replacing, andwiring renewed ; 4 amplifiers on one P.O.Rack for £25. Carriage £2.AMPLIFIERS. -l5 watts, Marconi Type 6,using 2-PX25, MHL4, rack mounting, com-plete with power pack, 200-250 volts 50cycles. meter, etc., less Valves, £6. Carriage7,6. A few incomplete but with trans-formers, 50/, to clear.CONDENSER LENSES. Plano Conveyoptically ground and polished. Post, 1/-,1(1n. Diem. 21in. Focus ... 7/8 each

31n. 10/- each4in. 28in. 15/- each4in. , 101n. mtd. irs. 32/8 pairSin. 9in. 30/- each6in.

HOUSES with10in. 38/8 eachLAMP HOUSES pair of tin. conden-

ser lenses, nd focusing mount, suitable forflood or spetlight, es.CINF3 PROJECTORS 16 mm.-" Ensign "silent, complete with Dallmeyer 21n. Super-lite lens, transformer and carrying case,£271101-.GB MODEL 1.516. -Sound, complete withvalves. lamps, lens, speaker, resistance, £55.

S27B.T.H. MODEL S.R.B.ound, complete,5.

METRO-VICK AUTO TRANSFORMERS.--230/110v., 500 watt, totally enclosed,£4/10/-.PHOTOFLOOD LAMPS, " Eke° " 1,000watt. I0/- each. Post 1/-

.LENSES.-Aldis anastigm at 1/2. Llin. focus(no iris), 50/- each.-DIM-BRIGIIIT FOOT SWITCH for con-trolling Photoflood lamps for 230v. 5 amps,32/6 each. Post 1/-.PROJECTION LAMPS. -115v. 750 w.Prefocus. Brand New, 25/-.BROMIDE PAPER, Slim it 5lln., glossy,soft, 7/8 per gross packet.RESISTANCE MATS. -Make ideal heatingmats for Aquariums, Photographic solu-tions. Print dryers, etc. Mains voltage,150 or 620 watts. Black heat, size 10in. x 61n.,2/8. Post free.HAND GENERATOR or Battery Charger.-6 volts .D.C. at 4 amps. contained in astrong metal case irith;automatic cut-out,very useful where no mains are available,could be converted to a wind charger. Only30/-. Carriage 51-.BALL BEARINGS. -No. EE2. lin. x lin.,31-, post free.THRUST RACES. -13/161n. x 116,post free.MTCROAMMETERS.-F.S.D.50.Flush type211n. dial scaled 0/100, contained in testset No. 28, 70/-. Complete. Post 2/-.VOLTMETERS. -0-300 A.C. Moving IronSilo. Flush or Surface Type, 25/-; 0-20,tin. Flush Moving Coil, 7/8 ; 0-40, tin. FlushM.C.. 1043 ; post 1/-.MOVING COIL METER with 1 M/Amovement, 211n. flush, rectifier type, scaled0/100 volts A.C. Resistance 100 k. ohms.A very useful basic meter, 30/-, post free.PORTABLE TEST METER. -Just thelob for the home constructor, in neat case,6in. x Sin. x 4in., reading 1.5, 3, 150 volts, 6and 60 mla. D.C., 5 k. and 25 k. ohms, 37/6.Post 1/6.HEADLAMP complete with BatteryCase. Fits on forehead. Leaves both handsfree, 7,6. Post V-.VEEDER, COUNTER 0-9999, lin. x lin. xSin. Very useful, 10/-. Post 8d.AERIAL RODS.-12in. long, }In. diameter.Any number of sections can be fitted to-gether. PA dozen, 61- for 3 dozen, 11/- halfgross, 20'- gross, £8 per 1,000.SLOW MOTION DIALS. -61n. Scaled0-100, reduction 200 to 1 or direct, ideal forwavemeters, signal generators, etc. Ourprice, while they last, 513. Post 1/-.FLASHING SWITCH UNIT with 6contacts. Full rotation 60 seconds, operatedby a Sangamo Synchronous Motor. 230volts A.C. 2 watts. In metal case, 3in. x2iin. x 21M., 15/-. Post V-.INTERESTED IN FISHING? -Then sendfor one of our tapered whip aerials andmake yourself a fine rod worth pounds.Consists of three tubular steel, seamlesscopper plated sections, 4ft. long, whichscrew into each other and are well finished,7/6. Carriage G.B., 2/-. Eire, 8/8.CUTTER HEADS.-" Recording" highimpedance. A bargain at 55/-. Post 1/-.STUART PUMPS. -230 volt A.C. motor,will lift 400 gals. per hour 15ft.. 111/15/ -larger size, -I h.P., 222/10/-. Carriage 7/13.

204, LOWER ADDISCOMBE ROAD,CROYDON



GALPINSELECTRICAL STORES

408 HIGH ST.,LEWISHAM,S.E.13Tel. : Lee Green 0309. Nr. Lewisham HospitalTERMS CASH WITH ORDER. NO C.O.D.All goods sent on 7 days' approval against

cash.EARLY CLOSING DAY THURSDAY

EX -NAVAL ROTARY CONVERTERS,110 volts D.C. input, output 230 volts A.C.50 cycles, 1 phase, 250 watts capable of 50%overload, weight 100 lb.. price E10/101.each, carriage forward.ROTARY CONVERTERS, 24-28 voltsD.C. input 1,200 volts 70 ni/amps, D.C.output, I0/- each, P.F.MAINS TRANSFORMERS (NEW),input 200/250 volts in steps. of 10 volts, out-put 350/0/350 volts 300 m/amps, 6.3 volts8 amps twice, 4 volts 4 amps, 5 volts 4 amps,70/- each, carriage 3/6 ; ditto, 450/0/450volts 250 m/amps, 6.3 volts 8 amps twice, 4volts 4 amps, S volts 4 amps, 70/- each,carriage 3/6 ; another, input as above,output 500/0/500 volts 250 m/amps, 6.3 volts8 amps twice, 6.3 volts 4 amps, 4 volts 4amps, 5 volts 4 amps, 75/-, carriage 3/6.Another, wound to (electronic) specifica-tions, 350/0/350 volts 250 miamps, 4 volts8 amps, 4 volts 4 amps, 6.3 volts 8 amps,0/2/6.3 volts 2 amps, 70/- each, carriage paid ;another, input as above, output 500/350!0/350/500 volts 250 m/amps. 6.3 volts 6 amps,0/2/6.3 volts 2 amps, 0/4/5 volts 4 ampstwice, 75/- each, carr. 3/6.MAINS TRANSFORMERS (NEW),suitable for spot welding, input 200/250volts, in steps of 10 volts, output suitablytapped for a combination of either 2/4/6/8/10or 12 volts 50/70 amps, 95/- each, carriage 7/6.MAINS TRANSFORMERS (NEW),200, 250 volts input, in steps of 10 volts,output/0, 6, 12, 24 volts 6 amps, 42/6 each,post 1/6. Another as above but 10-12 amps,55/- each, post 1/6 ; another, as above but25/30 amps, 75/- each, carriage 3/6 ; another,input as above, output 0/18/30/36 volts 6amps, 47/6 each, post 1/6.MAINS TRANSFORMERS (NEW),input 200/250 volts in steps of 10 volts, out-put 350/0/350 volts 180 m/amps, 4 volts 4amps, 5 volts 3 amps, 6.3 volts 4 amps, 45/ -each, post 1/6 : another 350/0/350 volts180 m/amps, 6.3 volts 8 amps, 0/4/5 volts4 amps, 45/- each, post 1/6 ; another500/0/500 volts 150 amps, 4 volts 4 ampsC.T., 6.3 volts 4 amps, CT., 5 volts 3 amps,47/6 each, post 1/6 ; another 425/0/425volts 160 m/amps, 6.3 volts 4 amps, C.T.twice 5 volts 3 amps, 47/6 each, post 1/6.MAINS TRANSFORMERS (by well-known makers). Input 100 and 230 volts,output 6 volts 1,3 amps twice, price 7/6 each,post 1/- ; another 200/250 input, output 25volts 4 amps C.T., 25/- each, carriage 1/6.MAINS TRANSFORMERS, 230 voltsinput, 150/0/150 volts 200 m/amps, 6.3volts 8 amps, 5 volts 2 amps output, 23/ -each.AUTO WOUND VOLTAGECHANGER TRANSFORMERS, tapped0/110/200/230 volts 350 watts, 55/- each,post 1/6 ; as above, but 500 watts, 70/ -each, carriage 3/6 ; as above, 200 watts,40/. each, post 1/6.EX-U.S.A. W.D. ROTARY TRANS-FORMERS, 12 volts D.C., input 500 volts,50 m/amps, 275 volts 100 m/amps D.C.output. Complete with smoothing switches,fuses, etc., as new, 17/6 each, carriage 2/6,can be run on 6 volts, giving half the statedoutput.MAINS TRANSFORMERS, input 180/250 volts, output 435/0/435 volts 250 miamps,6.3 volts 10 amps, 6.3 volts 8 amps, 6.3 volts8 amps, 5 volts 6 amps, 65/- each ; anotherinput as above. Output 4,000 volts 21miamps, 4 volts I amp, 2 volts 2 amps, 45/ -each.

SMOOTHING CHOKES, 4 henries,250 m/amps, D.C. resistance 120 ohms, 12/6each.CONDENSERS, 0.1 mid., 6,000 voltworking, 6/6 each.LARGE STUD TYPE DIMMER RESIS-TANCES, 10 ohms, 9/18 amps, 32 studs,35/. each.3 KILOWATTS DOUBLE -WOUNDVOLTAGE CHANGER TRANSFOR-MERS, 110/230 volts or vice -versa, as new,weight approx. 100 lbs.. f12/10/- each,carriage forward.RESISTANCE BOXES (sub standard),200 ohms, in steps (variable) by well-knownmakers, 37/6 each.ELECTRIC LIGHT CHECK METERS,useful for subletting, garages, etc., all for200/250 volts A.C. mains, S amp load, 19/ -each ; 10 amps, 22/6 ; 20 amps, 27/- ; 25amps, 32/6 ; 40 amps, 38/6 ; 50 amps, 46/6 ;and. KO amps, 57/6 each, all carriage paid.

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MAKE IT YOURSELF WITH OURREADY TO ASSEMBLE KITS

Tea Trolleys, TV Tables, Book Cases, Bedside Cabinets,Needlework Boxes, Coffee Tables, Foot Stools, Children'sChairs, Smokers' Stands, Standard Lamps, TableLamps, Chandeliers, Wall Lights, Candlesticks,

Marquetry Veneers.Send 6d. and self-addressed envelope for Illustrated

Booklet.

B. KOSKIE (Dept. A)72-76, LEATHER LANE, HOLBORN, E.C.IOpen 8.30-5.30. Closed I o'clock Saturday. Phone: Holborn 4777

PARKER'S SHEET METALHeavy Vice Model.Capacity 18 gaugeM.S. x 2ft. wide. -

Loose Attachments, ifrequired, for RadioChassis, Tray or Boxmaking.Weight 22 lbs. Price42/3. Attachments 1/6per ft. Carriage 41,With Attachments 5/8.

ALSOPARKER'S FOUR IN

ONE REVOLVINGDRILL VICEComprising :

Upright Vee.Inclinable Vee.Right Angle.Flat Side. Admitsstock of Sin. dia.Weight 13 lbs.Overall length 13in.

Price 42/6.Carriage 2/6.

Send for details.

A. B. PARKER

FOLDING MACHINE

WHEATCROFT WORKS, WELLINGTONSTREET, BATLEY, YORKS.

Telephone BATLEY 426.

Telephone: MUSEUM 9594

H. FRANKS58-60, New Oxford St., London, W.C.I

One minute fromTottenham Court Rd. Station

12/24 VOLTS HOOVER BLOWERMOTORS, Ref. 10KB/115, as recom-mended for car heaters in the Marchissue. Price 27/6 each.COMMANDO LIGHTWEIGHTPERISCOPES. Size 10in. x 4in. x lin.Ideal for sporting events, etc.. 10.' -each.

TUFNOL PULLEYS. Fitted ball races,external diam. 211n., internal diam.3 '16in., 219 each, 301- per doz.

DITTO. 41in. external, fin. internal,5/- each, 55/- per doz. 2,000 of bothtypes available.

DRIVING GOGGLES by Zeiss.Goertz, etc., supplied with spare set ofclear lenses. Set of anti -dazzle lenses.in maker's cartons. 11/- per set.

AIR TEMPERATURE GAUGES,Ref. No. 6A/510. fitted Mercury inSteel, Capillary Tube, Transmittingtype. Reading --30050+ Centigrade.Suitable for greenhouses. etc. Price18/6 each.

DYNAMOTORS. Ideal for car radio,Input 12v. d.c., 1.2 amps, output125v. d.c. 40 ma.

" KLAXON." 24 Volts d.c. shuntwound 1,20th h.p. motors, 2,500 r.p.m.continuous rating, 401- each.

WESTLNGHOUSE RECTIFIERSITS. Style 238 G.P.O. Input 200115.0volts a.c., 50 cycles, output ro voltsd.c.,14 amps.. 70 -. Carriage 10,'-.

MINATURE IMPULSE MOTORSmade by " Gents " size 3 x 2 xsuitable for operating models,switches. etc., operates off 4/6v.a.c.id.c. and is very powerful for itssize. Price 8,6 each, post paid.

SYNCHRONOUS CI.00K UNITS.Self-starting 200-250 v. a.c. 50 cycle.fitted Sangamo motors consumption24 watts, size 21In. diam.. 21n. deep,geared 1 rev. 60 mins. friction reset.Ideal movements for electric clocks.With gear train and Sin, hands. Price22'6 each, post paid.

SANGAMO MODEL S7 SYNCHRON-OUS MOTORS. 200/250 v. a.c. 50cycles, final speed 1 r.p.m., 2716 each.

SANGAMO MOTOR UNITS, MODEL7, final speed 1 rev. 24 hrs. 200,250 v.a.c. 50 cycles, 27l8 each.

SANGAMO MOTOR UNITS, MODEL7, final speed 1 rev. per 7 days, 21XIM0v. a.c. 50 cycles, 30'- each.

Ex _Air Min. GEAR PUMPS. TyPeRFP/1, made by Rolls-Royce, sizeapprox. 6 x 51 x 5in. Price 30:- each,post paid.

HOUR METERS, 200-250 v. a.c. 50cycles, 1/10th to 10,000 hrs. recording;ideal for life testing. process timing.etc., 42/6 each.

SLIDING RESISTANCES. Enclosedtype 20 OHMS 2.3 amp. Price 22/6each.

VARIABLE RHEOSTATS with screwthread control, 71 OHMS 4 amp., allnew, unused. Price 2211, post paid.

VARIABLE RHEOSTATS, fitted ver-nier control, 50 OHMS, I amp., allnew unused. Price 15/- each, postpaid.

ROTARY RHEOSTATS. If OHMS5'6 amps. Price 12'- each, post paid.

500 - OHM ELECTRO - MAGNETCOILS. 51 per doz.

60 - OHM ELECTRO - MAGNETCOILS, 10,000 available of both types,5,6 per doz.

SLIDLNG RESISTANCES. 3.4 OHMS12 amps. Price 22/8 each, post paid.

SYNCHRONOUS MOTORS. 200/250v.a.c. 50 eyes. with gear -trains. Finalspeed 1 rev, per hour. Ex -TimeOperated Units by well-knownmakers, size 31 x x 3In. Price 21/6.post paid.

DITTO 2 revs. per hour. Size 31 x 3 x 31.Price 16/6. post paid.

12 volt KLAXON HORNS, all new,16,6 each.

HAND GENERATOR POWERUNITS Type No 7 ZA 17571. giVing anoutput of 6 volts D.C. at 31/4 amps.,for charging. These are unused andhoused In metal cabinet 17 x 10 x 7in.,47/6.

LONDEX RELAYS, Type 220, Ref. No10F/494. two heavy break contacts.,24 volts, fitted in metal cases, 41n. xOn. x 21in., 816 each.

6 -VOLT LONDEX RELAYS, with 2break contacts, fitted 4 -way Jonessocket, 3/- each. 40i- per doz.

SOLENOIDS, Heavy Duty. 12;29 volts,d.c.. 10/6 each.

G.E.C. DOUBLE POLE CHANGE-OVER RELAYS, Platinum contacts,Coil resistance 2,500 ohms, 13'- each.

24 -VOLT MAGNOVOX HEAVYDUTY SOLENOIDS, 19'- each.

RECTIFIER UNITS, input 200/250volts, a.c.. 50 cycles, output 24 voltsd.c., 3i amp., £4 each.

STAINLESS STEEL HELIOGRAPHMIRRORS, 4 x 41n., 3/-.

CLOCKWORK MOVEMENTS fitted" VENNER " Escapement, runs 10hours one full wind, final speed 1 rev.75 sees. Price 9'- each, post paid.

" STANCOIL" U.S.A. 2.5 K.V.A. 50160cycle auto -transformers. Input; 1151250 v. Output, 110v. Completelyshrouded. £11 each.

FULL MAILING LIST PRICE 6D.



LETTERSr° THE EDITOR

The Editor does not necessarily agreewith the views of his correspondents.

Melting Milk Bottle TopsSIR,-With reference to the query by

Mr. H. G. Williams, of Twickenham(March issue), the idea of melting down milkbottle tops in sufficient quantities to makecastings is almost a practical impossibility,if, as he says, his only source of heat is alaboratory Bunsen burner.

In our school workshops we have success-fully melted large quantities of tops in acarborundum crucible on the forge fire,using coke as fuel and a variable speed fanblower for the forced draught.

As pointed out in your reply, oxidationand fusing must be overcome, and in orderto combat these troubles the tops must bebulked together in some way. For thispurpose we use a vice as a press, and an oldmetal bush about zin. bore as a die.

By this means we have, so far, recoveredabout 281b. of pure aluminium, which wehave cast into ingots of about rib, each.Allowing for loss due to unavoidable oxida-tion, our recovery is about 65 per cent., andwe reckon that about 2,000 tops are requiredto produce Ilb. of pure metal.

Whatever form of heating is used, it isimportant to note that melting should befairly rapid to prevent gasification, and thecrucible should be covered during melting.Pouring must also be done quickly asaluminium freezes quickly, especially whencasting thin sections. The life of the cruciblewill be prolonged if it is internally paintedwith a solution of water -glass before use,and cleaned out after each melt.

If your correspondent requires any furtherdetails I will be pleased to help him,if possible.-H. E. WHITE, A.M.S.E. (Derby).

SIR,-We, the undersigned, read withinterest the letter regardirig the melting

of milk bottle tops in the March issue ofPRACTICAL MECHANICS.

At our metalwork centre at Darnall,Sheffield, we melt them with a blowpipeand then add a little copper. From thisalloy we make castings for small dieselengines, ash -trays, etc.-F. PRINCE, D.PALMER (Sheffield).

Electric Chime Timing UnitSIR,-In the March issue of PRACTICAL

MECHANICS there appeared a letterfrom Mr. Jas. L. Sewell concerning myelectric Chime Timing Unit published inthe March issue of 195o under the nom -de -plume " Handyman.'

I have since made an improvement to theunit which may interest Mr. Sewell andothers.

In the published circuit the time lagbetween the first two notes depends on thetime the front door push is kept pressedonly (this does not apply to the trademen'sdoor push, which only sounds the last twonotes).

By connecting another condenser of similarvalue to the existing ones across the coilconnections of relay No. I we have a timelag also between notes one and two.

Should the push be rapidly pushed andreleased several times the first two noteswill not now be kept repeating, to be sedatelyfollowed by the third and fourth.

I might mention my own unit had a two-year test before the article was published,and is still in good order.

In conclusion I would like to thank MrSewell for his appreciative letter.-A. F.PARKER (Swanage, Dorset).

Toning WallpaperSIR,-With regard to the above query of

C. S. Brown in the February issue ofPRACTICAL MECHANICS, I would say that itwould be impossible to evenly stain or tonea grained imitation wood wallpaper withoutobliterating the printed pattern unless itwas sized first to prevent the stain penetratingthe paper. This is best done after the paperis hung.

A practical method is as follows : Paste thepaper rather liberally with good strong pasteand allow to soak for some minutes. Severallengths of paper can be pasted at one time,folded to delay drying, and hung in sequence.When dry, the wallpaper is sized by applyinga coat of hot jelly -size, using a clean dis-temper brush, and brushing on lightly toavoid frothing. Re -heat the size as the workproceeds, and make sure that the whole ofthe surface is covered. When dry, a secondcoat of size is applied. When bone dry, thewallpaper may be stained to the desireddepth with a " scramble " stain such asMander's " Matsine," thinning this out todirections and applying sparingly and evenly.As an alternative, a stain could be mixed upusing " burnt umber ground in oil," mixedquite thin with equal parts of linseed oil andturpentine, and adding a small quantity ofpaint dryer. If this is thought too warm intone, a little green could be added. If jelly -size is unobtainable, the packeted powderedsize can be made up to the directions andallowed to cool and " jell " to test thestrength. It should set like a weak table -jelly.

The surface can afterwards be coated withcopal varnish if a glossy finish is desired, andit will then give many years of service.-H. POSTLETHWAITE (Easton Grey, Malmes-bury).

" The Mystery of Time "SIR-The opening sentence of that

portion of your editorial dealing with theabove subject implies, I believe, that timeextends infinitely into the past and willextend infinitely into the future. I suggest toyou, however, that, in the light of presentknowledge, this is by no means certain.

Dunne, in his " Experiment in Time "(which, by the way, was not a " novel"),conceives that time does not " flow " nor dofresh events keep on happening in it but thatall events, both (to us) past and future,happen together simultaneously and that itis our consciousness that travels throughthese events observing a cross-section ofthem only, corresponding to our " present,"as it passes. This theory appeals to me asproviding the only adequate explanation forthe undoubted occasional occurrence ofcases of precognition of " future " events.But Dunne, who I think wrote his book before'the implications of the theory of relativity' were widely known, still conceived an infinite

series of events stretching away from our" present "- in both directions.

We are taught that space is not infinit0but curves back upon itself to form a boundless but finite whole in much the same waythat the surface of the earth-in two dimen-sions-is also boundless but finite. Now," space " and " time " are in modern teachingclosely inter -related and it therefore seemsto me unlikely that a finite space can existin infinite time. Relativity teaches us that foreach individual " observer " time has adifferent meaning and a " time " in whichno space and hence no observers exist canhave no meaning at all ! I suggest, therefore,the probability that, like space, time is alsofinite and curved back on itself so that, in it,only a finite number of events take place. Toround off such a theory we may speculatethat the total time length possible in ourparticular cosmos is equivalent to the time itwould take a beam of light to travel roundfinite space and arrive back at its startingpoint (though the idea of an expandinguniverse and hence an expanding time raisessome difficulty).

Summarising the foregoing we arrive at acosmos in which both " space " and " time "are finite and in which, therefore, only afinite number of " events occur and occursimultaneously. Through it each " observer's "consciousness travels observing only thatcross-section of these events which corre-sponds to his individual " present." Itis to be noted that an " observer may equallywell be you or I, a prehistoric man existing

a super -intellectual50,000 years ago orexisting 5o,000 years in the future (as weimagine it). In this cosmos cccasional cases

and are due to aof precognition occurtemporary shift of the " observer's " con-sciousness from his individual " present "to some other cross-section of the events.

ed either by someor to a loosening

The shift being causabnormal circumstanceof the tie binding his consciousness to hisown " present " during sleep.

What happens when the " observer's "consciousness has travelled full circle is

ugh no more difficultinfinity. The views

difficult to conceive thothan trying to conceiveof yourself and of other readers of your paperon this and the foregoing ideas in general

T. H. MORRISmight be interesting. --(Farnborough).

Einstein's TheorySIR,-I thank Mr. P. H. Jackson (Buxton)

for his reply to my letter (PRACTICALMECHANICS, December issue), but am stillunable to appreciate that there can be anydifference whatever in the time a 'plane wouldtake for an out and back journey acrosswind compared with the same lengthout and back journey parallel with thewind. I feel there is something wrongwith his premises and/or calculations. If,for instance, one works out his figures for,say, three examples where the wind speedin relation to 'plane speed is progressivelygreater, the results show increasing disparitiesin times, and if a wind speed of 75 m.p.h.and a 'plane speed of too m.p.h. are used thedisparity between the times is so great as tobe very improbable.

I think the true conditions are that in thecross -wind flight the 'plane, in order to keepon its ground course, must trim its centreline towards the wind at an angle to theground course equal to the proportions ofwind speed to 'plane speed. Thus, if the'plane speed is too mp.h. in still air and thewind speed is 25 m.p.h. the 'plane will beturned at an angle which results in the 'planefacing the equivalent of a direct head wind ofone-fourth of the wind speed of 25 m.p.h.,viz., 6f m.p.h. The 'plane's net speed alongthe ground line will thus be 93f m.p.h.which, if the distance out and back is 200



miles, gives a time of 2 2/15111 hours-pre-cisely that occupied by the 'plane out and backparallel with the wind.

So far as I can see, any theory whichresults in different times for the two journeyswould be just as impossible in practice asis .perpetual motion.

As regards my possibly unfortunate choiceof a book on the subject, I have since readanother book by one of the best-knownphysicists. His way of showing that the outand back cross -wind journey would take ashorter time to accomplish than a similarjourney parallel to the wind is by assumingthe cross -wind journey to have been done instill air-a second example of what appearsto be a wrong appreciation of the conditionsaffecting the Michelson-Morley experiment.-C. W. CARR (Eastbourne).

Interplanetary Space TravelSIR,-In the March issue, Mr. P. Mansfield

(Interplanetary Space Travel) statesthat a rocket at the commencement of firingis only concerned with gravity as air resistanceV' and V=O. Whilst it is true that gravityin regard to the rocket must be overcomewhen firing commences, it is also true thatair pressure affects the rocket's thrust froma pressure ratio point of view.

Thrust T. is equal to the product of themass flow of gas -d-t and the exhaust velocity

Ve, when the gas is expanded in the nozzleto a pressure equal to that of the surroundingatmosphere. This is called momentum thrustand the gas is said to be correctly expanded.Thus, a rocket with a chamber pressure of3751b./sq. in. and a pressure ratio of 25: Iwill have an exit pressure equal to that of thesurrounding atmosphere at low altitude ;

i.e., islb./sq. in. We then have To=--Ve.dt

If the rocket ascends, and the atmosphericpressure decreases, say, 21b./sq. in.,the change has no effect on the gas in thenozzle, as it is supersonic. It does, however,introduce pressure thrust T.. This can bedefined as the product of the differencebetween the exit pressure Pe and theatmospheric pressure Pa, and the exit areaof the nozzle in sq. ins. A. The extra thrustin the above case, then, is 131b. multipliedby A, and may be stated as T.-A (Pe -Pa).

We see, then, that the total thrust Tavailable from a constant fuel consumptionair pressure ; the total thrust being

expressed as T=-dt +(Pe -Pa) A.It is easily seen from this that a rocket's

fuel consumption would be less for take -offin a vacuum than for take -off in Earth'satmosphere.

Another aspect of air -resistance is theobvious one of drag. The rocket cannotattain any velocity whatsoever unless airmolecules are displaced by the shaped nose.Drag due to cross-sectional area may bereduced, but skin drag then tends to increase.As a result, any streamlined form is but acompromise with air -resistance.

It is correct that much of the heat energyin the gas -stream is converted to kineticenergy through the nozzle. When we considerthat in free space, where the exit pressure iszero, the pressure ratio term is at maximumand the pressure ratio is infinite. All heatenergy is then convertible to kinetic energy ;but this is impracticable as the nozzle wouldneed to have an infinite exit area.

The suggestion that the rocket may moveat a velocity far in excess of its own exhaustvelocity is quite logical when consideringprojection in free space. The constant thrustadding to the ever-increasing velocity of therocket would continue so long as the fuelheld out. The maximum velocity, previouslystated, would be in respect of fuel allocated

for the outward journey and not the maximumof the " all -burnt " state. The motorcertainly would be cut-with at least so percent, of the fuel unburnt.

After all, one may wish to return. Oh yes,we should have forward motors capable ofsupplying thrust for speed reduction andmanoeuvring.

It would indeed be tragic that, havingexplored a new world, you were preventedfrom returning home through lack of fuel.Not only would your strange and wonderfulodyssey be lost to mankind for ever, but yourextinction would be imminent.-WailAmELLWOOD (Hatfield).

Alarm Clock Switching DeviceSIR,-The following drawing is of a simple

device to make an alarm clock operatea switch. It is, to the .best of my belief,original.

The idea is to enable a domestic clock tobe used without any drastic modifications.The drawing is self explanatory and the ideaand dimensions can be adapted to any clockwhere the alarm key revolves when the alarmrings. The hole receiving the falling ball isobviously located in a suitable position but,if necessary, a small funnel could be added toallow for slight deviations in its path.

The end of the centre contact -leaf isinsulated to isolate the ball from any livemetal work. The paper clip which holds theball is of bent wire, but can be modified tosuit any winding key.-EDWARD A. STOTT(Rochdale).

A/armclock

Wood beading locatesclock on base

A/arm key

Paper clip

72°Dia.steelball

esk Hole receivesfallen be/I

VA/AC/LIM

Box builtaround contacts

S.Por OP changeovercontacts removedfrom PO type relay\::\x.\ N.\ %

OIL

\\ \\\\\ \\\\\\\\\\\\\\k\\Weight of be/I

operates contactsCentre leafextended andend insulated

Side view of the alarm clock unit, and detailof the switch.

A Recording WeathervaneA Correction

TN the article on the above subject in the.L March, 1953, issue af PRACTICALMECHANICS, a draughtsman's error occursconcerning the two cog -wheels. The wheelat the end of the vertical shaft should meshwith the bottom of the cog -wheel on thehorizontal shaft, and not the top of the wheel,as shown in Fig. I of the above -mentionedarticle.

International Radio Controlled ModelsSociety

THE International Radio ControlledModels Society announces that its

Annual International Contests for RadioControlled.Models will be held at Southend-on-Sea, Essex, England, on July 25th and26th, 7953.

A contest for radio -controlled model boatswill be held on Saturday, July 25th, andcontests for radio -controlled model aircrafton Sunday, July 26th. The aircraft sectionsof these contests, comprising a contest forpower -driven aircraft and a contest forgliders, are held in accordance with the F.A.I.Regulations for International Contests. It ishoped 'that a large number of competitors,both from Great Britain and from overseas,will take part in these contests. Furtherdetails and entrance forms will be availablesoon to anyone who may write for informa-tion.-R. ING, 36, Sunny Gardens Road,Hendon, London, N.W.4.

Harrow and Wembley Society of ModelEngineersTHE locomotive section committee has

devised a series of locomotive trials, tobe known as the " Arthur Pole MemorialTrials." A formula which will enable thesmallest 3jin. gauge . locomotive to competeon equal terms with the largest Sin. gaugelocomotive is being worked out by the com-mittee. A shield will be awarded to theowner of the locomotive giving the bestperformance during each season.

Starting on April 19th and on the thirdSunday of each month until September loth,a series of invitation days have been arranged,when individual clubs will be invited to runtheir engines on the society's 70oft. track atthe British Railways L.M. Region sportsground at Headstone Lane, which is nowbeing overhauled in anticipation of a busyseason ahead.-Hon. Sec., K. D. CARTER, 21,Stanley Road, Northwood, Middlesex.

Aylesbury and District Society of ModelEngineers

R. ALLNUTT gave a talk to thesociety on March 18th on the making

of tunnels. A large number of membersturned up at Hampden Buildings to heartheir colleague talk on a subject on whichhe is well informed. Mr. Allnutt is byprofession an Admiralty civil engineer withquite- a lot of experience of railway work.He illustrated his talk with lantern slidesobtained from the London Transport. WithMr. East operating the lantern, he managedto throw light on what for some memberswas a very dark subject.-Hon. Sec., E. H.SMITH, Mulberry Tree Cottage, DevonshireAvenue, Amersham, Bucks.

BOOK REVIEWEDModel Steam Locomotive Designs and

Specifications. Revised by Ernest A.Steel. Published by Cassell and Co.,Ltd., 62 pages. Price 4s. 6d. net.THIS book, which is a revision of an earlier

work by Henry Greenly, gives speci-fications and brief constructional details ofvarious types of model steam locomotivesfrom No. o gauge to a i5in. gauge " Pacific "locomotive. There are also chapters onFundamentals of Design; Cylinders and ValveGear ; Boiler Design and Handling ModelLocomotives. The book is well illustratedwith line drawings, including 20 practicalworking designs.



MYFORD M.L7. LATHES bench and Cabinet models from stock.Bench models £48.5.0. Deposit £12.2.0

and 12 monthly payments of 68/7. alternatively deposit £12.2.6 and 18 Monthly paymentsof 47/11. WE PAY CARRIAGE OUT. Literature gladly sent.

BOXFORD MODEL C. SCREWCUTTING LATHES ONCABINET STAND (less motor) £142. Deposit £35.10.1 and 12 monthly

payments of £9.12.7, alternatively deposit £35.10.11 and18 monthly payments of 86.13.8. Carriage extra. Literature gladly sent.REEVESCO DOUBLE ENDED SLIDING TAILSTOCK DIE -HOLDER fzem.hoguiuMana npc=1.antlep.klg.or31N. :.,grly:T. shank (please

FOBCO STAR 0-4" CAP. DRILLING MACHINES ii;g,;, tiggmachine 835.8.8. fitted Jacobs chuck. Deposit 88.17.9 and 12 monthly payments of 50/11.PEDESTAL MODELS 2404.9. Deposit 810.2.9 and 12 monthly payments of 57/-. THESEMACHINES NOW AVAILABLE FIrr.s.D WITH No. 1 M.T. SPINDLE WITH DRIFT (leaschuck). WE PAY CARRIAGE OUT. Illustrated literature gladly sent.

REEVESCO NO. 2 bench drilling machines for belt drive 0- fin. cap. £8.12.6complete with chuck. Deposit £2.3.0 and 12 monthly pay-

ments of 1110, Carriage and packing 7/6 extra.

SELECTA 6" DOUBLE ENDED BENCH GRINDERS pAae 81IngleDeposit 81/- and 12 monthly payments of 2215. WE PAY CARRIAGE OUT. 4iin.DOUBLE ENDED PORTABLE GRINDERS A.C. single phase £7.19.0. Deposit 40/- and 12monthly payments of 10/11. Carriage paid.

PROGRESS JUNIOR BENCH DRILLING MACHINESfor belt drive 0-lin. cap. complete with chuck £13.5.0. Deposit 66/3 and 12 monthly paymentsof 1813. 0 -lie. cap. with motor mounting (less motor) complete with chuck £22. Deposit£5.10.0 and 12 monthly payments of 30/3. WE PAY CARRIAGE OUT.

PERFECTO 5" STROKE HAND SHAPERS £1.5.17.6. DePosit 79/5and 12 monthly pay-

ments of 21110. Machines fitted with Auto feed £17.17.6. Deposit 89/5 and 12 monthlypayments of 24/7 Carriage and packing 7/6 extra.

BURNERD CHUCKS FOR DIRECT FITTING TO MYFORDM.L7. LATHES (no backplate required) 4in. 3 -jaw G.S. model 30M. £7.19.3.

6 -in. 4 -jaw Ind. model 34M 26.5.0. Post paid.

HAIGHTONS S.S. and S.C. centre lathes, complete with C/S. unit and motorPulley, aln. 4 -jaw Ind. chuck with screwed body (less motor) 825.17.9.

Deposit £6.9.9 and 12 monthly payments of 35/7. Carriage and Packing 76 extra. Illus-trated literature gladly sent.ALL GOODS DESPATCHED INSURED AGAINST LOSS. AND DAMAGE IN TRANSIT.REFERENCE TO CARRIAGE ABOVE APPLIES TO MAINLAND ONLY. Overseas carriagestrictly extra.A 1/- stamp will bring you a copy of our 1953 comprehensive illustrated catalogue. withdetails of blueprints, castings, fittings and materials for many " L.B.S.C." designed small

_ steam locomotives. Also listed carefully selected range of workshop equipment most ofwhich is available on our well-known OUT OF INCOME TERMS.

A. J. REEVES & CO.413, MOSELEY ROAD, BIRMINGHAM, 12Grams: Reeyesco, Birmingham." Phone : CALthorpe 2554

"THE CHOICE OF EXPERIENCE"

[ 41.p. Split Phase Start

ELECTRIC MOTOR

YOU SAVE 43/-Record No. 84 steel Fitter'svice. Slightly used but inexcellent condition. Madeof steel throughout andunbreakable in use. Hard-ened steel law plates.Width of jaws 41in., depth3M., opening 511n. Weightapprox. 41 lbs. s4List Price £8.3.0Carr. 4/9 England and Wales.

Induct ion motor by11.T.11., 220/230 volt singlephase. 1,425 r.p.m. Rest -Dent mounting. New, butslightly store s5soiled,Carr. & pkg. 6/8 Eng. & Wales,

8/9 Scotland.

_GA NI AG E SSPECIAL OFFER OF 'BMX ' FLEXIBLE

VICES SHAFT DRILLSL5.10 OFF List Price!

Ideal for light grinding operationson castings, pottery, sheet metal,welds and light metal. Takes plainprofile wheels up to 3in. diam.Shaft size 4ft. x 8 mm. 1 h.p. motorA.C./D.C. 6.000 r.P';£1 2/i oList Price £18.

Or 3 gns. Deposit and10 monthly payments of 20/9Carr. & pkg. 5/- Eng. or Wales.

DOUBLE -ENDSPANNERSin ClipSlimly made. Drop forged from manganese siliconsteel. lin. to tin. Whitworth. Tensile strength90-108 toils per sq. in. Black finish with .1 6,_bright heads. - Setof Six. 6 I

Post & Dig. 1.1-

* New and Enlarged Edition of GamagesTools and Motor Car Accessory List

Free on Request.

STURDY STEEL SECTIONED.

FOLDING BENCHDesigned to be securely fixed to wall or otherupright structure. When closed it projects only4tin. and the tool rack provides a lock -up fortools. On release of fastener it is dropped.to work-ing position with bench top level and rigid. Benchtop surface comprises 101n. wide steel plate and2ft. 5in. wide timber. Fitted with vice. Ht. ofback Oft. 3M. In. of bench 2ft. bin. Bench topaft. 31n, x lit. Pin. Wt. approx.100 lbs. A6/11/6Carrlage outside our van arm 9/3 England or Wales.

GANIAGES, HOLBORN, LONDON, E.C.1. HOLborn 8484

TECHNICAL

SHRUBLAND

THERMOSTAT.mic Case tin. x tin.fully adjustable over240 volts. 3/9, postTHEROMOSTAT.with magnetic snapTanks. 5/8 each,THERMOSTAT.stetstat for Space Heatersture Ovens. 15 amps.,40/80 deg. F. 2.5/-,TIIERMOSTAT.Electric Immersion90/190 deg. F. 1521/1510. post 9d.THERMOSTAT.stat. 15 amps., 2.50x tin. A beautifulranges 30/90, 40/100,as required. 82/0/0,THERMOSTAT.volt A.C. For control

THESERVICES

CO.WORKS BANSTEAD SURREY

Telephone: BURGH HEATH 3830

post 4d.Panel

9(1.,

1 amp..between

for

3/8

A mostinPrice

ohms/yd.

Blanket.20/-.

Blanket.35/-.

LA/40 BI -Metal. Cera-x fin. 50-220 am F.this range. 1 amp.,3d.

5N/40. As above butaction, ideal for Fish

post 3d.CS. ConvectorLINEThermo

and Low tempera-250 volts A.C.

post 5d. .

MB. for control ofHeaters up to 3KW.

amps., 250 volts A.C.

PP. Room Thermo-volts A.C. 5in. x llin.

instrument. Temp.40/80, 60/100 deg. F.post 6d. .

BW/1. 3 amps., - 250of hot -plates. vul-

ranisers,, etc. 50-550 (103. F. 15.6,TOGGLE SW ITCH. Single HoleMounting 250 volts, 2 amps. SamplePost 3d. 7/8 per doz.SERIES PARALLEL SWITCH.250 volts A.C. Fits into line cordappliance and supply. 7/6, post 3d.

CORD THROUGH SWITCIIcontrol of small portable domesticappliances. 5 amps., 250 volts A.C.each, post 3d.ASBESTOS HEATING CORD.versatile heating medium. Stocked15, 25, 200 and 400 ohms per yard.P. per yard.P.V.C. HEATING CORD in 200only. 1/- per yard.DRAWING AND INSTRUCTIONSfor making a 60in. x 30in. Electric1/6. Heater Cable and blueprint.DRAWING AND INSTRUCTIONSfor making a 60in. x 501n. Electric18. Heater Cable and blueprint.

FINE SILVER. CONTACT RIVETS for light arid medium duty.

Ref.HeadDiem.

(in.)

Headthickness

(in.)

ShankDiem.(in.)

Shanklength(in.)

Type ofhead

Priceper doz.

110111113110124199

211321

- 837A837/1

.062

.062

.091.075

.125 '

.156 .

.18.235.250.250

.020

.020.030.031.030.062

.062

.080

.047

.047

.050

.048

.050

.078

.091

.185

.094

.094

.025

.040

.035

.120

.065

.062

.235

.165

.050

.050

Hedlund,,

FlatRadjused

FlatRadiused

1/-1./-1/92/92/96/-8/-

121-151-12/-12/ -

All post free : For Gross Price multiply doz. price by six.

ASBESTOS DISCS. 5in. diem., tin.thick. Ideal as Soldering Iron rests. 2/-doz.. post 64FIRECLAY TUBES (Soft). 15/64in. O.D.a 11/641n. I.D. x 2in., 1/6 per doz., post 4d.PURE NICKEL CONTACT STRIPS,lin. x 51161n. xhigh temperature elements.1/6 per doz., post 3d,BAKELITE KNOBS with Aluminiumriveting shank, for use as feet or lidhandles,

ADHESIVE THREAD. 3 strand. 100yard Tins. A very useful item. 7- tin.BEST BLACK RUBBER TUBING.1/321n. Wall. Internal diameter lin., 5d.per foot ; 3/16in., 6d. per foot ; lin. 7d.per foot 5/16in 8d. per foot; M.,' 8d.per foot.SCREWS. 4 B.A. x lin. C/S(Machine Cut). Gd. doz., post 3d.

5 B.A. x tin., C/S Steel. Gd. doz., post 3d.6 B.A. x lie., Brass N.P. 44. per doz.,

post 3d.6 B.A. x 3/161n., Brass N.P., 4d. per doz.,

post 3d.

Grommetts (or Cable Bushes). Black rubber.Ref. No. O.D. I.G. Per doz. Per gross Pos'3030R Td i5" 2/- 14/6d. 4d.3032 _2_''

16 7/33' 2/3d. 16/6d. 4d.3028 111-" 9/32" 2/3d. 16/6d. 4d.3031 9 ,,is li'ff 2/0d. 14/6d. 4d.2029 9 ,+'

TS' 7/33' 2/0d. 16/0d. 4d.5019 _9 ',

Fe' 1" 1/11d. 15/0d. 4d.133 19/38" II-" I/10d. 13/6d. 4d.

1033 -ta" r 2/3d. 16/6d. 4d.

PORCELAIN INTERLOCKING INSULATING BEADS. ANERIOD BAROMETER

14 4* '

This fine instrument is ofhandsome appearance andwould normally cost 05/5/0.An exceptionally advantageouspurchase enables us to oilerat 55/- or 5/- dep. Balance11/- monthly. A perfect " Wed-ding Present."

C [--Size

Bore(im)

Diam.' (in.))

No. per Price pergross

1

34568

.047

.070

.091

.118

.141

.156

.196

.111175

.211

.243

.300

.419

.453

100726461443630

8d.9d.1/-1/42)44/66/8

Post : 4d. for gross lots. Orders over £1 post free.

FINE. SILVER TIPPED CONTACTSCREWS.7 B.A. x lin., 4/- doz. 4 B.A. x lin., 6/- doz.8 B.A. x On., 416 doz. 6 B.A. x lin., 513.doz.III -METAL. 6in. x lin. x .0361n.. 1/- perstrip. 1 kin. x 3/161n. x .0361n., 6d. per strip.MAGNETS. Sintered Bar magnets ofgreat power and stability for snap actionthermostats, as used in tropical aquaria.Ain. a 3/16in.x 1/16in. 91. each. 8'- per doz.CERAMIC ELEMENT FORMERTUBE. 5in. long. 7/161n. outer diam.,lin. bore. 30 grooves per inch. For makingsmall Immersion heaters. 2/8 each. post4d.FLASHING LAMPHOLDER for win-dow displays, signs etc. Inserts in any

B.C. lampholder. 40/100 watts. Mako ashow for the Coronation. 71 each.CHATTERTON'S COMPOUND. 4 oz.sticks. 1/6 per stick, post 3d.UNIVERSAL MAINS MOTOR. Length3 1/16in. 25 Watts, 230/60 volts. A.C./D.C.Shaft diam. 5/321n. 6,000 r.p.m. (light).Ideal for Hairdryers, Drink Mixers, etc.3$1-, post 6d.FOUR BLADE BLOWER FAN to fitabove motor spindle. 2/-, post 4d.ELECTRIC HAIR DRYER. Ilot andCold Air, 200/50 volts. A.C./D.C. A won -derful gift for girls of all ages. 23/8/0 or5/- dep., Balance 11/- monthly Guaranteedfor 12 months.


344 NEWNE$ PRACTICAL MECHANICS May, 1953

Build it yourself with these

CLASSIC EXAMPLESOF TO-DAV'S OtTSTANDING HI-FI EQUIRMENT

Everything for the Quality SpecialistFOR CASH OR EASY TERMS

A Selection from our Stocks of TAPE RECORDING EQUIPMENTWearite Tape Deck - £35.0.0Bradmatic Tape Desk £42.0.0Truvox Tape Desk £23.2.0Lane Tape Desk ... ... £16.16.0Simon 2B ... ... ... £60.0.0Scophony ... ... ... ... ... £65.0.0Ferrograph ... £79.10.0C.J.R. Portable ... . £119.10.0Quad Tape R. ... ... £16.16.0Bradmatic Circuits ... 5.0Bradmatic 6 RP Heads ... ... £3.15,0Bradmatic 5 RP Heads ... ... ... ... ... £3.5.0Bradmatic 5E Erase Head £3.5.0Spare Spools, 600 ft. ... 4s. 6d.: 1,200 ft. ::: 6.6Tapes, G.E.C., Scotch Boy or F.M.I. ... ... £1.15.0

GRUNDIG, VORTEXION, E.M.I., WIREK, etc. MICROPHONES, etc.

FULL RANGE OF AMPLIFIERS, includingRogers Baby de Luxe £22.10.0Decca P.A.6 ... ... ... ... ... £26.5.6Goodsell Williamson .... .. ... ... £33.5.0

Also DECCA, LEAK ROG ERS, SOUND SALES, etc.

SPEAKERS, includingGoodmans 101 8 in. £7.2.9Tannoy Duo Concentric 15in. ... £33.10.0Wharfdale 10in. Golden ... £8.6.0

MOTORS, PICK-UPS, includingGarrard RC75A ... £16.18.6Decca GU4 ... £9.19.11

Send for full lists. We also specialise in large -screen TV.

THE CLASSIC ELECTRICAL ,T.;352'364, LOWER ADDISCOMBE ROAD, CROYDON, SURREY.

Telephone . ADOtscorribe 6061-6062.

EX-GOV. BARGAINSCHORE HORSE LIGHTING SETS. x2-15 v. zo a. (30o w.). Completeready to use with control box, ammeter, etc. Fully Automatic and self-startingfrom 12 v. battery. Runs over 05 hrs. to the gal. Slightly used and guaranteedperfect, i16.1o.o each. Two 6 v. 85 a. bats. to suit, f6.to.o. Carr. Paid.MK. 32 TELESCOPIC RIFLE SIGHTS. 34 with E. and W. adjustments,i7.1o.o each.MOTOR BLOWERS. 24 v. A.C./D.C. Mk. III. Used, 02/6. New boxed,17/6. (See P.M. July. Hedge trimmer.) Transformer to suit, 07/6.RADIO RECEIVERS. 6 v. 121124, complete with valves, 301- each. HugeQuantity of Radio Gear. See our lists.DELAYED ACTION TIME SWITCHES. With 8 -day jewelled watchmovement. Adjustable from 1 hr. to 36 hrs. by a pair of cal. dials. Brand Newin sealed tins, 21/- each.DRAWING INSTRUMENTS. Slightly soiled. Will do all that a £to setwill do, price 02/6 each.

OPTICALENLARGER KITS. 35 m. or 21 sq. All parts ready to assemble with opticalcondensers and achromatic lens. 98/-. Plans only 3/6.MICROSCOPE UNITS. 14X. Use with your ordinary camera for photo-micrography. Makes an ant look like an elephant, 45/- each. Cost to times theprice. This unit has numerous uses. See our Booklets Nos. t and 2, 2/6 each.SMALL EPISCOPES. Make your own. Lens and Mirror with plans, E7,6.TELESCOPES, ASTRO or.TERRESTBIAL. Make your own. It's dead easy.We have a wide choice of achromatic OGs and Orthoscope eyepieces at prices tosuit your pocket. See Booklets No. t and 2 for details, 2,6 each.TELEPHOTO LENSES. Ideal for adapting to Exacta or similar camera".All approx. F5.6. Brand New and Bloomed throughout. 5M. back focus 3in.,40/-. 8in. bf 4in., 45/-. loin. bf 6in., 50,'-. All in plain, screwed sleeve.No iris. EX TUBE to fit the lens only, 7/6.BOOKLET, " HOW TO USE EX -GOVT. LENSES& PRISMS," No. 1 Sr 2,price 2/6 each.3D. Don't be mislead about this subject. It's neither difficult or expensive .

if you go the right way about it. Get in on the ground floor. Our New Book" Stereoscopic Representations of Three Dimensional Scenes,"price 7/6, tellsyou all you need to know about 3D. Without Viewers or gadgets. For Cine,stills or prints. Colour or monochrome.

Please send S.A.E. for complete lists.

H. W. ENGLISH,RAYLEIGH RD., HUTTON, BRENTWOOD, ESSEX

L

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Workshop Practice Industrial Electronics Surveying Personnel Management

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Machine Tools & Metrology P.M.G. Certificates Carpentry & Joinery Costing

Marine Eng. Radio Amateurs Licence Builders Clerks Office Practice

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Tracing Installations & Wiring High Speed Oil Engines A.R.B. Licencss

Jig & Tool Design I.E.E. Theory garage Management A.R.M. Certificates

Also Examination Courses fon - General Certificate of Education, B.Sc. (Eng.), Common Preliminary, A.M.I,Mech.E.. A.M.I.C.E., A.M.I.Strucl.E.,A.M.Brit.I.R.E A.F.R.Ae.S., A.M.I.P.E,, A.M.I.I.A. A.M,I.M.I., A.M.I.11. & V.E., M,R.San.I., A.M.I.San.E., A.M.I.Munc.E., A.M.I.E.D., A.M.S.E., L.I.O.B.Also CIT.( and GUILDS Certificates in Mechanical. Electrical, Aeronautical, Automobile, Telecommunications and Structural Engineering: Refrigeration, -

Heating & VentRatien. Courses also provided for all branches i POST NOW"Please send, without obligation, the above FREE BOOK.

E.M.I. Institutes, Dept.I44k 43 Grove Park Rd., London, W.4Home ExperimentalKits now form part ofthe following courses:Draughtsmanship,Carpentry, Chemistry,Photography, Commer-cial Art, Radio andElectronics, etc.

Eubject(s) which interest me

Name

Address


May, 1953

The World oModel Steel Works Tableau Scale Model

Ambulance Prize Sailing Ship

AT the International Machine ToolExhibition at Olympia last year therewas displayed a series of working

models in tableau form which depicted steelproduction over the past hundred years atthe works of Messrs. Samuel Osborne andCo., Ltd., of Sheffield. The models were toa scale of tin, to 'ft., and the scale -modelfigures included in the tableau were made bystudents of the Sheffield Art School. Thefirst three models showed a crucible melring

shop, a pair of old-fashioned water -driven hammers and a rolling mill, all ofabout a hundred years ago. Model No. 4(Fig. 2) represented a 6 -ton Heroultelectric arc furnace, as used nowadays forproducing large steel ingots and castings,and included .exact reproductions ofmelting -furnace equipment. The electricfurnace is tilted so that the melted andrefined metal is poured into a ladle,raised by a crane, carried to the castingpit and the metal poured into the mouldsthrough a stopper in the bottom of theladle.

Fig. t shows another realistic model, that

Fig. 5.-Modelyachts and sailingships at the ModelEngineer Exhibition.Mr. Field's cham-pionship model ofthe " Cutty Sark "is in: the glass caseon the extreme left.


Fig. t (Left).-Modelof a 4 -ton hammer

shop.Fig . 2 (Below).-Model of a 6 -tonHeroult electric arcfurnace. Both of theseare part of a tableauof working modelsdepicting s t eel pro-duction over the past

hundred years.

Figs. 3 and 4.-Two views of the illoth full-size model of a Karrier Ambulance,presented to the Lancashire County Council by County Alderman Harry Lord.

345

of a 4 -ton hammer shop. Compressed airnow supplies the power instead of a water-wheel, and the heat of the furnace is con-trolled. In the forge, ingots are hammereddown to billets or slabs, suitable for rollinginto bars or sheets. A modern double -duo rolling mill was the subject of anothermodel.

Model YachtsThe imposing display of model yachts and

sailing boats shown in Fig. 5, and looking asthough they are lined upfor the start, were seen atthe Model EngineerExhibition.Presentation

AmbulanceThe fine model ambu-

lance displayed in Figs. 3and 4 was made to theorder of County Alder-

, man Harry Lord, M.B.E.,J.P., and was presentedby him to the 'LancashireCounty Council. T h epresentation was to com-memorate the inaugura-tion of the AmbulanceService under theNational Health ServiceAct, 1945, and the modelis to be used as a trophyfor competition amongstthe personnel of theservice to encourageefficiency. The scale isone -tenth full size.



4-

Wolf Electric Tools at BIFWOLF ELECTRIC TOOLS, LTD., are

exhibiting the complete range of theirelectric tools at the B.I.F. and the displaywill incorporate some interesting newcomersto the already extensive list of industrialmachines. There will be a new saw (typeRS7), a new portable grinder (type GQ6) anda die grinder kit (type DGi).

The RS7 saw is a smaller counterpart ofthe popular min. saw and incorporates a

Wolf " Cub" equipment built up as a wood turning lathe.

new powerful motor of advanced design. Ithas a 7in. blade, is extremely compact andeasy to handle and possesses abundant powerfor high-speed cutting at full capacity. Tothe range of portable grinders is added theGQ6-a heavy duty model which ispowered by a new motor with exceptionallyhigh speed -torque characteristics, and it isfitted with a resinoid bonded grinding wheel.

The DG I die grinder kit. has beenproduced to meet the demands of industryfor a versatile tool at low cost to tackle thenumerous jobs in their tool rooms and main-tenance departments. The power -unit ofthis kit is the well-known Wolf high-speedgrinder, type EVG3.

Qualified technicians will be in attend-ance to provide continuous demonstrationsof the Wolf range of portable electric toolsincluding --drills from I' -in. to I tin. capacity,screwdrivers, grinders, polishers, saws,blowers, hammer kits, hisel mortisers, valveseat grinders, valve refacers, valve seatgrinding kits and the popular " Mobilectric "valve shop.

Apart from the full range of electricsolderguns and soldering irons, there will beworking displays of the fascinating Wolf"Cub " equipment for handymen and homeconstructors. The basic power unit is a tin.drill, which with the various accessories caneasily be built up into a drill press, portablepolishing, grinding or sanding kit, a woodturning lathe or a circular saw bench.

Pill LiteratureTHE free literature supplied by the Petrol-

eum Information Bureau, 29, NewBond Street, London, W.', includes "NotesAbout Oil," which is an account of theorigin and early history of oil and the typesof strata in which it is found. Prospecting,drilling, refining and transportation are alsodealt with. Additional pamphlets on thevarious aspects of oil production include

such titles as: Drilling an Oil Well, Refiningof Oil, Transportation of Oil, Drilling forOil in England, Chemicals from Petroleumand Jet Aircraft Fuels. A set of three 4oin.by 3oin. two-colour wall charts on searchingand drilling for oil and its refining are avail-able, price 4s. 6d. including P.T. and postage.Films, film strips, episcope photographs,lantern slides, sets of samples, molecularmodels and display material are available forfree loan on agreed dates.

Johnsons Developer468

TOHNSONS OFj HENDON, LTD.,have produced a newand improved M.Q.developer, known asDeveloper 468. Inpowder form thiscompound containsdeveloper improver142 and wetting agent326. It is supplied ina tin to make 200Z.for subsequent dilu-tion I to I for con-tact paper and I to 3for bromide.

The developer hasbeen evolved to pro-duce an intense blue -black on all types ofcontact paper a n dcopying papers, to

have great exposure latitude and completefreedom from fog. Developer 468 is alsoexcellent for bromide papers and permitsprolonged development without risks ofstains or veiling. Instructions are enclosedand the special two-part container keeps thecontents in perfect condition. The 4o-80oz.size retails at 25. 9d.

Britinol Soldering OutfitTHE " Popular " soldering outfit consists

of a "'Ilium)! " self -blowing spiritlamp, a telescopic soldering iron, a coil of

C; 1111.1J POPULAR,,-4M M

7000"

The complete " Britinol" soldering outfit.

" Britinol " self -fluxing wire solder, a tinof paste solder and a pair of extra wicks forthe lamp. The lamp is self acting, easilylighted with a match, and has no valves toget out of order. It gives an intense heatand clean blow pipe flame Sin. to 4in. long.The lamp cannot leak when folded for thepocket and has folding supports to carrythe soldering iron.

This iron has been specially designed foruse on the supports of the " Britinol " self -blowing lamp and will fit into the pocketwhen closed. The paste solder comprisesfinely powdered tin and lead, combined witha non-acid flux of great cleaning power. Thewire solder contains a core of the same non-acid flux. Each of these items is available

separately and the complete kit, packed ina strong, partitioned, cardboard box costsI6s. 3d. The makers are Bi-metals (Britinol)Ltd., St. Mary's Works, Bridge Road,London, N.9.

"Truset" Rani Precision BendingMachineECONOMY in tube bending, especially

where off -set bends are required, canonly be effected when the straight lengthof tube between the bends is as short aspossible. To tackle this problem Chamber-lain Industries Limited, of Staffa Works,Leyton, E.io, have designed and producedthe Truset Bending Machine incorporatingan improved back stop with the centre form-ing block. The whole idea is based upon theback stop being as narrow as possible andyet so designed as to give the necessary gripand support to prevent slipping and distor-t on to the tube during the bending opera-tion.

The bending machine on its light steel stand.

Precision bending to accurate dimensionsis ensured by the back stop, attached to thetube former, adjusting its grip automaticallyin accordance with -the load applied, a featurewhich will be appreciated by engineers whohave suffered with tube slip. Formers areavailable for bending, cold and unloadedthrough any angle up to 18o deg., tube sizesup to a maximum of Sin. (gas tube) anddia. in copper and light gauge tube.

Another advantage of this machine is thecunning design incorporated in the centre pinand handle to ensure that the correct angleof lead is maintained at all times. This isimportant, as too little will cause draw andtoo much, flatting, and is essential for theaccurate bending of copper and light gaugetubing. Of course right and left hand bendswell beyond 18o deg. can be produced inany completed form.

The machine consists of two main com-ponents-the base and bending arm. Thebase is circular and carries lugs suitable fof,universal mounting on either bench, vice, orbending stand, and around the base are holesfor a stop -pin, which when used in conjunc-tion with an additional stop screw on thebending arm, allows adjustment to anyangle for repetition work. The bending arm,rotating about a centre -pin fitted to the base,consists of two accurately machined steel bars'carrying an adjustable bending pin, fitted intothe head block at one end, and the handleblock at the other, this design rendering the)arm extremely robust.

A light steel fabricated bending stand, illus-trated, can also be supplied with the machine.

A small pipe vice can also be suppliedfor mounting on the stand so that the, tubecan be secured for further processing.



READERS' ZA122. AHD liY,H11'2,The pre -paid charge for small advertisements is 6d. per word, with box number 1/6 extra (mtnimum order 6/-). Advertisements,together with remittance, should be sent to the Advertisement Director, PRACTICAL MECHANICS, Tower House, Southampton

Street, London, W.C.2, for insertion in the next available issue.

SITUATIONS VACANTThe engagement of Persons aifswering these

adverttsements must be made through a LocalOffice of the Ministry of Labour or a scheduledEmployment Agency if the applicant is a managed 18-64 inclusive or a woman aged 18-5)inclusive unless he or she, or the employment,IS excepted from the provisions of the Notifica-tion, of Vacancies Order 193.).

xyAMINE TOOL FITTERS,-Lira Machinists, Turners, with well-.

, established firM; Box No. 101, c/oPRACTICAL MECHANICS.

CROWN AGENTS for the Colonies.-Cinema Officer required by the

Government of Nyasaland for thePublic Relations Department for onetour of 24 to 36 months with pros-pect of pensionable employment.Commencing salary according to age,war service and experience in scale,£677 rising. to £1,001 a year; includ-ing cost of living allowance ; outfitallowance, £30 ; free passages ;liberal leave on full salary. Candi-dates, between 24 and 35 years- ofage and UNMARRIED must be ableto manage a mobile cinema, maintainand repair film projectors, radiosets, tape recorders and ' domestic

-mechanical appliances. They mustalso be able to maintain a filmlibrary. Apply at once by letter,stating age, full names- in blockletters, and full particulars of quali-fications - and experience, and men-tioning this paper to the CrownAgents for the Colonies,' 4, Millbank,London, S.W.1; quoting on letterM.33495.E. The Crown Agents can-not undertake' to acknowledge allapplications and will communicateonly with applicants selected forfurther considetation.

EDUCATIONAL

WANTEDURGENTLY, Teachers

of Handicraft. CorrespondenceCgurses, best preparation Writeonly, specialised. College Secretary,Marriott's, Bushby, - Leicestershire.,Success assured.

BECOME A TEACHER of Wood-work or Metalwork. Interesting

well -paid work with pensionablesecurity. Long holiday& No previousexperience required. Expert rapidpostal coaching; -low fees. -Booksprovided free. Send now for freeprospectus, Dept. 24, ChambersCollege, 148, Holborn, London, E.C.1.A M.I.Mech.E., B.Sc., CITY &Ilk GUILDS, Etc. Guaranteedpostal courses for all Exams. andTechnical Divisions from Elementaryto Degree standard. Approximately95% successes. 144 -page prospectusfree on request. B.I.E.T. (Dept. 967),17, Stratford Place, London, W.1.FREE ! Brochure giving details of

courses in Mechanical and Pro-duction - Engineering, Draughtsman-ship, etc., for the A.M.I.Mech.E.,A.M.I.P.E., City and Guilds, andother Professional ex amina tions.Train with the Postal TrainingCollege operated by an industrialOrganisation ; moderate fees. E.M.I.Institutes, Postal Division, Dept.PM30, 43, Grove Park Road, London,W.4. (Associate of H.M.V.)I P.R.E. TECHNICAL PUBLICA-

TIONS. 5,500 Alignment Peaksfor superheterodynes, 5/9 ; Data forconstructing TV aerial strengthmeter, 7/6 ; sample copy ' The Prac-tical Radio Engineer," quarterlypublication of the Institute, 2/;membership and examination data,1/-. Syllabus of I postal coursesfree and post free. Sec.. I.P.R.E.,20, Fairfield Road, London N.8.

FOR SALEHOUSE SERVICE METERS, credit

and prepayment; availablefrom stock. Universal Electrical. 221,

'City Road. London, E.C.1.CIOMPRESSOR EQUIPMENT. Mis-

cellaneous Items; catalogue, lid.Price. 157, Malden Road, Cheam.

COMPRESSORS for sale. 3 CFM,1801bs. sq. in., on metal base,

with driving wheel and receiver,price £3. h.p. Heavy Duty Motors:price £3 ; carriage forward. Wheel-house. 1. The Grove. Isleworth.(Phone : Hounslow 7558.)

TRANSFORMERS, for trains, weld-ing, low voltage lighting, battery

chargers, etc. ; all transformers'fitted with earth protection "screen, " play safe." Write or phoneyour requirements to F. W. Whit-worth, A.M.Brit.I.R.E., Model Dept.,Express Winding Co., 333, LondonRoad, Mitcham. (MIT. 2128.)QYNCHRONOUS CLOCK MOTORS.KJ' 230v. A.C. S/Ph 50c., 12/6 each,plus 1/-. Postage Universal Elec-trical, 217, City Road, London, E.C.1.

NUTS, BOLTS, SCREWS, Rivets,Washers and hundreds of other

items for model engineers andhandymen; Send now for free list.Whiston, New Mills, Stockport.

D UPLEX Decorative Transfers,Coronation Trawlers. Trade -

marking Transfers. List and samples,6d. " P.M.," Axon Harrison, Jersey.

AMAZING DEVICE, cuts perfectdiscs, wheels, etc. to 12in. dia-

meter, with any circular saw, 10/6 ;p.pd. ; sample gin. mahogany disc,photo, details, 1/6. Below:-H OW TO RE -MIND and Service

Electric Motors,' Generators.Complete Practical Book only 3/- ;p.pd. Below:-

OW TO MAKE IT -BOOKS :Whittling in Wood ; Inlay Pic-

tures,' Marquetry; American- ActionToys ;. 21 Lovely Lamps ; each p pd.

BUILD YOUR OWN PHOTO Equip-ment, 12 designs in two book&

Enlargers, printers, dryers, timers,etc., 6/- ; p.pd. Below:-

40POWER TOOLS You Can Makefrom scrap, pipe fittings, etc.

This amazing book of plans for cir-cular Saws, lathes, band -saws, . jig-

-saws, planes, tapping attachment,jigs, etc., has sold 250,000 copies, andis a " -must" for every home work-shop, 12/6 only ; p.pd. Below:-

.

L.M.ERICAN BOAT BUILDERSAnnual : 28 boat plans, 8-22ft.,

and other helpful articles,. 7/6 ;p.pd. Below:-CAR BODY REPAIRING. Complete

A B C course ; Illustrated.;7/6 ; p.pd..; lists free. A.P.S. (P),Sedgef ord, Norfolk.

QMALL DENTIST'S SYRINGES,Sbeautifully made all metal

instruments by leading makers. Allparts heavily plated, and machinedfrom solid. Smooth positive action.Lapped piston and cylinder. Pistonrod calibrated 0-20. Ideal for pre-

' cision lubrication without mess, andmany Miler purposes. Complete with6 strong hardened steel needles, inplated metal case with hinged lidand fastener. Ex -Ministry, new, un-used. Worth ££££s. Our price'9/6, post 6d. K. W. Logan, West -alley, Hitchin, Herts." CONSTRUCT Your Own Refrigera-

tor." This book, written by arefrigeration engineer, is profuselyillustrated with drawings and photo-graphs and tells you, not only howto construct a Cabinet or Built-inRefrigerator, but illustrates manythat have -been built by amateurs andare operating satisfactorily, 3/6, postfree. Obtainable direct from authorand publisher, Robert C. Scutt,Refrigeration Engineer, 52, HadleyWay, London, N.21.

B RASS PINION WIRE for drivingwheels, etc., for model makers,

10 teeth x approx. lin. diam., and 6teeth x approx. kin. diem.;- anylength up to 10ft., at 1/6 and 9d.per foot ; sample and postage 1/-.Armstrong, 55, Old Hall Street, Han-ley, S.O.T.

" PICADOR " ROTOSAW. Portablecircular saw attachment for

your electric drill fitted with 4incircular saw bigde, adjustable fenceto cut up to fin, in depth, ideal forwood, plastic or soft metals ; 33/-each, post paid. Lambs -wool polish-ing- Bonnets, 5in., 4/3 each : RubberBacking Discs, 5in., complete withkey, 4/6 each; Abrasive Discs, 5in.,6 assorted grades, 2/-. Send 2W. forlists of Saw spindles, Vee Pulleysand Belts, Plummer Blocks, etc.Sawyers, Ltd.. St. Sepulchre Gate,Doncaste

PERSPEX," clear, coloured, sizescut, also Corrugated , Plastics,

Aluminium, Asbestos, Mouldings.Henry Moat & Son, Ltd., AtomWorks, Newcastle, 1.

AIRCRAFT SURPLUS, FlexibleDrive, 48in, long, brass unions

each end, outer casing tin. dia., 10/6each. Also Nuts, Bolts., etc. S.A.E.for list. Hulse & Goddard, Bux-worth, Stockport.

LENS WORKERS : Supplies ofAbrasives. Lists available.

Mason & Gantlett Limited, 3, OrfordPlace, Norwich.

REJUVENATE your Water Softener;New Zeolite, 2/3 lb. ; 101b. post

paid. C. G. Nelson, 118, AnchorwayRoad, Coventry.

.V.LECTRIC MOTORS, B.T.H. 230/240, i h.p., 1,425 r.p.m. ; new

and unused; £5/5/- each. Miniature12 or 24v. Motors-, A.C/D.C.; idealfor models, etc. ; size attn, long. x2in. x New Twin 40w. BallastUnits, no starter required ; all vol-tages, 200/250 supplied ; 25/- ;requires holders and lamps only tocomplete ; Single 40w. Units, S/H,17/6 ; Holders, 2/6 each ; Starters,2/6 each ; 24v. Vent Axia Fans, new,45/- each-; Crompton ParkinsonChlorinator Pumps, 220v., 230v., A.C..

h.p. ; little used ; £10. HarringayPhotographic and Electrical' Supplies,Ltd., 423, Green Lanes, N.4. (Tel.;MOU 2054.)

TO OTARY CONVERTER, 230v., D.C.,aa to 230v., A.C., 200w.; £10 ; s.a.e.for bargains list of Transformers,Rectifiers, Valves, etc. Lawrence,134a, Cranley Gardens, N.10.

FASCINATING St - eel Tr acingMachines for copying and en-

larging from newspaper and magazinedrawings, sketches; interesting; 5/-,post free.-Clayton. 16, WestminsterRd., Bradford, Yorks.

.SAW BENCHES, 7in. 24/151-, 8in.£5/10/-; Combination Lathes,

£10; Planers, £9/10/-; Motors,Spindles. Send 4d, stamp for com-plete illustrated booklet. H.P. avail-able. James Inns (Engineers),Marshall Street, Nottingham.

THE " LEADER" in its class. Theunrivalled " E.W." Lathe. Con-

vertible from plain lathe to handtraverse, backgear, and screwcuttingby just adding the appropriate unit.Send for details (20. stamp please).Credit terms-You can obtain an" E.W." for as little as £4/4/- down.Protect your tools and equipmentfrom rust. A packet of ' V.P.I. "paper will do the job. Send 3/9 fora packet, or stamp for details.Wanstead Tool Supplies, 48, HighStreet, London, E.11.

,SUPER KALEIDOSCOPES, 2/9;carriage paid. Schofield, 5,

Turner Buildings, Luddenden Foot,Yorkshire.

POLARIZING KITS, assortedlaboratory grade screens for

simple adaptation to any size astro.or terrestial telescopes, microscopes,cameras, etc.; suitable for astro.daylight observation, micro. analysis,colour and cloud photography, gemtesting, 3D cinema viewing, etc.; withexperimental specimens and illus-trated instructions, detailing applica-tion, principle, experiments in half -and full -wave extinction, etc., price10/- box; sample screens, 2/6 pair.-Below.

ATOMIC KITS, reveals actualsplitting of atoms, alpha particle

bombardment. etc. Harmless; lastsfor centuries ! Comprising of minia-ture nuclear emitter and targetscreen built into micro, slides, with100X area microscope and instruc-tional data; price 10/-; without micro-scope, for use with own, 61 -.-Below.ZAMBONI (VOLTAIL) PILES, 1,500

volts. inexhaustible potential forstatic electric experimenting, charg.ing electroscopes, etc.; size 1 x 9iin.,8/6 ea.; c.w.o.; all post free.J. K. M, Holmes, " Scientific Instru-ments," Dept. P.M., " Vizcaya,"Wolveleigh lice., Gosforth, NeWeastle-on-Tyne, 3.

80w* DIA., 24in, focus, TelesconSobjectives, achromatic, 42/- ;

high power, iin. approx. astro eye-pieces, 35/-, L. Allen, Marble Place,Eastbank St., Southport.

MAKE YOUR OWN RANGEFINDER.Full instructions, 3/6, post free;

or instructions and material, 11/-.Elgin, Dept. S., 338, Lillie Road,London, S.W.6.

BALL -RACES, 3/16in., iin. bore, 1/6each, 12/- dozen; tin. bore, 3/ -

each; Bevel Gears, 3 pairs 7/6;Camera Controls. £2/10/-; UniversalJoints, ideal for models, take tin.or 3/16in. spindles, 5/- each;, 6 or12 volt. amp. Rectifiers, 10/6;Control Boxes for model railways,containing 2 ceramic rheostats,switch, and 2 -pin plug and socket,10/6; Indicator Units with 6 -voltbulbs, 5/-; small Electric Motors,24 volt, 2iin, long by ltin. diameter,A.C./D.C., 20/-; 0-1 M.A. Meters; 20/ -and 25/- each; s.a.e. enquiries.Bateman, 110, Peartree Road,Derby. (Phone: 44528.)1DERSPEX for all purposes, clear or

coloured, dials, discs, engraving.Denny, 15, Netherwood Road, W.14.(SHE: 1426, 5152.)

"AC " Sparking Plugs off U.S.radio equipment, 3/9 each;

Paxolin Strip, 8iin. x kin.- x 3/161n,20. each, 2/- doz.; packing free;postage at P.O. rates. Send s.a.e. for6 -page list of bargains. The RadioServices, Lr. Bullingham, Hereford.

EARTH LEAKAGE TRIPS, half-price, Siemens 30 -amp., G.E.C.

15 amp.; as new. Prices from BoxNo. 103, C/0 PRACTICAL MECHANICS.

MODEL DEALERSATTENBOROUGH Model Railway.'

Model railway specialists ;finest in the Midlands . Agents for,and stockists of, many well-knownfirms. Why not ask for -a copy ofour A.M.R, Chronicle ? The latestinformation regarding our stock, 1/-,post free.. -82, Arkwright Street, Not-tingham, and 64, Narborough Road,'Leicester,

QHIPS IN BOTTLES.-The construc-tional kit that tells you how to

make them ; build for pleasure orfor profits.; kits 6/- ea. from HobbiesLtd., and model shops. Cooper -Craft Ltd., The Bridewell. Norwich.

MARINE MODEL SPECIALISTPlans, Engines, Fittings, 1/32in.

and 1/16in. Ply Stripwood, Timber,Radio Control Equipment, Boat andYacht Kits, Galleon Kits and Plans.J. Chappell, 393-5. Eccles New Road,Salford, 5.LONDON. - Robson's Hackney's

Model Shop. 149-151. MorningLane, E.9. (Tel.: AMHerst 2928.)

BUD MORGAN, The Model Special-ist, 22, Castle Arcade, Cardiff.

(Telephone: Cardiff 29065.) ModelAircraft, Trix, Tri-ang, GrahamParish, Model Railways and Galleons;first-class mail order service Sendfor my 1953 price lists, price 3d.

HOBBIES LTD. have over 50 years'experience of catering for the

needs of modellers, handymen andhome craftsmen. Branches at 785,New Oxford Street, London, and inBirmingham, Glasgow, Manchester,Leeds, Sheffield, Hull, Southamptonand Bristol. Head Office: Dereham,Norfolk.

HORNBY DUBLO CONVERSIONS,Duchess, Gressiey 2 -rail scale,

52/6, 3 -rail scale, 42/6; Tankers 2 -rail,42/6, 3 -rail, 32/6. Sheffield ElectricalModel Engineers, Shalesmoor,Sheffield.

MODEL -MAKERS and Mechanics !Here is the simple -to -operate

Blow -lamp for all soldering jobs; theBritinol Self-acting Spirit Blow -lamp;price 7/-, or gd. extra post and pack-ing, direct from Bi-Metals (Britinol)Ltd., Balfour Mews, Bridge Rd.,London, N.9. Illustrated list s.a.e.

(Continued on next pogo)


348 NEWNES PRACTICAL. MECHANICS

(Continued from previous page)

THE B.R. ELECTRICAL PLASTICINJECTOR. The only machine

on the market for compression plasticinjection moulding at a reasonablecost. Makes toy soldiers, brooches,etc.; no smell; no trouble; nochemicals; plastic sets immediatelybone hard; works off lightingcurrent; no experience needed ;makes 100 articles for 4/-. Samplearticle free. New list of brooch andfarmyard animal dies; machine diesand plastic supplied ready for use.The toy soldiers are better than anylead soldiers. The only machine ofits kind in the world; price £8/10/-.Write for details of the machine andfull list of moulds, all free, to : TheSmall Power Machine Co., Ltd.. 4,Sunleigh Parade, Alperton, Wembley,Middlesex. (Wembley 1383.1

MODEL MAKERS. You need toolsand materials. Send s.a.e. for

free copy of our catalogues. Ken-nion's of Hertford.

HOBBIESHOBBYISTS, handicraft workers,

send 6d. stamps for our illus-trated catalogue, " Perspex " Jewel -craft, Flowercraft, etc NewingCo., 96, Grove Vale. London. S.E.22.TOY CASTING MOULDS, soldiers,

sailors, airmen, animals, etc.;catalogue, 9d.: Moulds for Plaster -work, plaques, ornaments andCoronation souvenirs. Moulds from3/6 ea. ; catalogue, 9d. ; s.a.e forlist. F. W. Nuthall, 69. St. MarksRoad, Hanwell. London, W.7.

GROW wonderfully decorativeminiatures of Real Trees by

secret Japanese methods; fascinating,profitable hobby. Send 8/6 forguaranteed guide and selection ofseed, or s.a.e. for details: MiniatureTrees. Dept. 90, Room Two, 3,Bloomsbury Street, London. W.C.1.TOLLS HOUSE FITTINGS and

Papers ; Wooden and Metal ToyWheels (trade supplied) ; illustratedbrochure ; s.a e. Jasons. 135, NagsHead Road. Enfield. Middlesex.

WIRING ACCESSORIESAll goods are of well-known manu-facture and carry a money -back guar-antee. C.O.D. or C.W.O. All carriagepaid.CABLE.-TRS Flat Twin, 1.044, 55/- :3.029, 75/- 7.029, 1151-. PVC SheathedFlat Twin, 1.044, 52/8 3.029, 70f-.All per 100 yds. PVC Cables aresuitable for both interior and exteriorwiring, and can even be burled in theground. All types and sizes of Cablesavailable in 25, 50 or 100 yd. coils.Heavy cables cut to desired length.Switches, 1/8 ; 2 -Way, 2/, CeilingRoses, 10d. Lampholders, 10d. 3 -PinSw. Sockets, 5a., 4/6 15a.. 6/8. Weoffer a complete service and can supplyalmost anything electrical. Advice..on Installations gladly given. Sendfor Lists.

HUNT & CO.,STEPCOTE HILL, EXETER

OF::EDSDAYS APPROVAL

to aII PRACTICAL MECHANICS readers

Packed with facts, figures and data!4(X) pages instruction, reference, diagrams.tables I Immense contents, Include lathework ; small tools ; filing ; fitting andmarking out : dividing bead ; micro-meter, vernier ; mensuration. screw -cutting ; gear-cutang ; hardening, tem-pering ; electroplating : silver soldering :brazing : welding soft soldering ; pa-tents, etc. Get it NOWON APPROVAL! POST COUPON NOW .1to loonosego so-cs:1-wo-e- I os 11111/UTo: A. THOMAS & CO. (PMI), III,Buchanan St., Blackpool. Send P.M.H. onAPPROVAL-I enclose 13/3 OR send C.O.D. I

can return hock w thin 5 days for full refund

Name

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WATCHMAKERSGET YOUR TOOLS, Materials and

Spare Parts from Western WatchSupplies Ltd., 17, Yorke St., Wrex-ham. Send 6d. for lists.yNTERCHANGEABLE Watch Parts,1- Balance Staffs, Winding Stems,Centre Wheels, complete BalanceAssemblies, Hands, Buttons, Main-springs, Tools ; send for lists. H. S.Walsh, 28, Anerley Station Road,London. S.E.20.

WATCHMAKERS' SCREWDRIVERS,high tensile blades, swivel top ;

set of 5 graduated sizes, in fittedbox, 5/-, post paid. Sawyers. Ltd..St. Sepulchre Gate, Doncaster.

WATCH REPAIRERS and Experi-menters. -10 Geneva watch

movements from Gold and Silvercases, accept 20/- the 10 ; 10 Eng-lish Lever Movements, capped andjewelled, 30/- the 10 ; 10 assorted1 -plate English Lever Movementsfrom 18ct. Gold cases, 50/- the 10.Merkel's, Jewellers, Grey Street,Newcastle -on -Tyne.

HAVE YOU A WATCH you areunable to get repaired ? If so,

send it to us by registered post forestimate, no repair too difficult ; allwork guaranteed. The Melnor Horo-logical Dept., 32/2, Waterloo Road,Nottingham.

WOODWORKINGTYLER Spiral Hacksaw Blades cut

in any direction at conventionalhacksaw speed without turning thework, 10in. Hacksaw Blades 4d. eachfrom leading tool dealers. Write toSpiral Saws, Ltd., Trading Estate,Slough, for details.

WOOD LATHES, Attachments,Motors and control Gear, Circu-

lar Saw Blades, Spindles or Benches,Turning Tools, etc. Interested ?Then send 6d. for our illustratedcatalogue, No. 529. D. Arundel &Co., Mills Drive, Fariadon Road,Newark, Notts.PLYWOOD. -3/16in. Finnish Birch,

very clean, sanded stock ; 4sheets, 30in. x 30in., 18/- ; carriagepaid. Stamps for lists of mouldings.plywood and complete woodworkers'supplies. Sawyers, Ltd., St. SepulchreGate, Doncaster.

MAHOGANY PLYWOOD, anyparcel £1 ; delivered ; c.w.o.

Following new: 5 at 111 x 66 x lin.,6 at 23 x 20 x tin., 12 at 14 x 26x lin, 14 at 14 x 23 x in., 20at 14 x 17 x fin., 30 at 14 x 14x fin.. 20 at 42 x 51 x lin., 32at 45 x 31 x lin., 8 at 66 x 51 xlin., 20 at 23 x 6 x fin.,16 at 78 x 5 x 3/16in., 12 at78 x 51 x 3/161n. Following oneside slightly glue stained: 5 at 33x 23 x 3/16in., 7 at 23 x 23 x3/16in., 16 at 47 x 9 x 3/16in. M.Leader (19201. Gosford Street,Middlesbrough.

HANDYMEN.-New Timber, sound,seasoned, selected, thicknessed,

neatly bundled. Send for list. fin.x lin., 11/3; fin. x 21n, 22/3; lin, xlin., 17/4; fin. x 21n., 32/3; lin.3in., 48/6; lin. x lin., 21/6; lin.x 21n., 39/9; lin. x 3in.. 63/-; lin. x4in., 85/6; all per 100ft. run; goodlengths; immediate delivery; minimumorder 20/-; c.w.o.; carriage paid.Generous sample bundle, 15/-.Blacknell (Dept. 75), Farnborough,Hants. (Phone: 106.)

The ' Adept BenchHand Shaper

Length of stroke ofram slim.

No. /12, II Shaper, 8 lin.stroke. 1t Price 25 15s, 0.1.

Price £16 17s. 8d. Postage and packing 341 (U.K.). TheArI1/554, rawer Adept ' 21in. lie. B.S.P. 4 -Jaw lode -

4 pendent Chuck. Reversible Jaws, 38,8.F. W. PORTAS.S, MACHINE TOOLS, LTD.

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IMPETUS Precision PLANERSCircular safety type cutter -head Highquality tempered steel knives. Tablesmounted on machined inclined ways.Ground table -surfaces. Fencesadjustable to 45 deg. E9.10.04 in. MODEL.Motorised. £18.10.0. 6 In. MODEL228.10.0. Motorised £44.0.0. Send forCatalogues of other Impetus ' Products.JOHN P. M. S. STEEL, Dept. SO,

SINGLET. YORKS.Phone : BINGLEY 3551 (4 lines).

PLASTICSsold ; Perspex sheets and offcutsin stock, large quantities of clearand coloured, Acetate sheets and

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Phone: LAB. 4457.

MOTORISED SAW BENCHESStandard Range from 6in. to 301n. Saws.Complete with Saw and motorised.61n. 611.15.0. 8in. 213.19.6. 121n. £16.10.Or supplied unmotorised for your power.Spindles. Bearings, Motors. Pulleys,Belts.Send 10d. for Illustrated Catalogue -Handbook of Saw Bench and Trans-mission design data.Beverley Products, Ransk114 9, Notts.

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DRAWING SERVICESBARGAINS in Drawing Instru-

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HANDICRAFTSltfUSICAL MECHANISMS, Swiss17-1- made, for fitting in cigaretteboxes, etc., 22/6 each. Send 6d. forcomplete list of handicraft materials.Metwood Accessories, 65, ChurchStreet, Wolverton, Bucks.

WANTEDWANTED, Polish No. 3 Mine

Detector for ferrous- and non-ferrous metals. Platts (Matlock). "Ltd., New Street, Matlock.

PHOTOGRAPHYENLARGER and Camera Bellows

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BOOKLETS " How to use ex -Gov.Lenses and Prisms," Nos. 1 and

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4 vols., with data sheets; first-class condition; £2/10/-. Jones,Angeldown Farm, Wantage, Berks.

BUILD YOUR OWN REFRIGERA-TOR, all components available

at reasonable prices. Frigidaireflowing cold units, £5; small units,Kelvinator, etc.. £4; f h.p. heavyduty Motors, £3; Chrome Cabinetfittings, new, £1; -money back guaran-tee; s.a.e. for list and schematicdiagram. Wheelhouse, 1, The Grove,Isleworth, Middx. (Phone: Hounslow-7558.)

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AIR PISTOLS

CAN YOU PLAY THE PIANO?If you are a music lover, why have you not se-QUIred this enjoyable accomplishment 1 Has the

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QUERIES andENQUIRIES

A stamped, addressed envelope, three pennystamps, and the query coupon from the currentissue, which appears on the inside of back cover,must be enclosed with every letter containing aquery. Every query and drawing which is sentmust bear the name and address of the reader.Send your queries to the Editor, PRACTICALMECHANICS, Geo. Newnes, Ltd., Tower House,Southampton Street, Strand, London. W.C.2.

Use of Proportional DividersT HAVE been presented with a pair1 of proportional dividers madenearly a century ago which I hope to usein my work as a draughtsman.

There are four scales marked on thesedividers, three of which I am not sureabout. One scale for lines I have used ;the others are marked " circles,"" planes " and " solids." Please adviseme what proportions of " planes "" circles " and " solids " can be found bythese dividers and how the scales havebeen arrived at. -E. Denham (London,N. x6).

THE scales are arranged to give the pro-portions marked on each scale as below :

Lines : Give proportionate lineal measure-ments.

Planes : Give proportionate areas.Solids : Give proportionate cubic contents

or volumes.Circles : Give the side length of a polygon

when the opposite points are set to the radiusof the circumscribing circle and the fulcrumjoint index has been set to the number ofsides required for the polygon. To use theinstrument, set the joint against the numberof sides of the required polygon, open thelong points to the radius of the desired circle,then the short points are at the requiredseparation equal to the length of the polygonrequired.

The way the scales have been arrived at isas follows :

Lines : Index gives direct proportionbetween lengths of the long and short legs.

Planes : Index gives proportion betweenlong and short legs, arranged to equal thesquare root of the index number. For instance,should you set the Plane Index to " 3" andopen the long legs to the length of side of asquare area, the other legs will give the lengthof a square of one-third the area.

Solids : In a similar way the index heredivides the lengths of the legs in proportionto the cube root of the index numbers.Should you set Solid Index to " 3 " and thelong legs opened to the length of side of, say,a tank, the other will give the length of sidesof a tank of one third the capacity.

Circles : The index is set to give the correctlength of side when the long legs are openedto the radius of the circle circumscribingthe desired polygon, the index setting beingequal to the number of sides in the requiredpolygon.

Reducing Vacuum Cleaner Discharge PipeBore

T WISH to utilise my vacuum cleaner toI supply air under pressure for use withblowtorch and paint gun. How can I bestreduce the 2in. diameter outlet to a boreof, say, in. so that I may use a lessunwieldy pipe, without excessively affect-

ing the efficiency of the unit ? Can Iincrease the discharge pressure ?

Will you please advise me on the designfor a coal-gas/air blowpipe for use withwhatever method you may advise for useof the vacuum cleaner. I need as smalla flame at as high a temperature aspossible.

The discharge pressure of my cleaneris approximately .45 lb. per sq. in.(ruin. water gauge pressure). -A. L. N.Stephens, (Kingston -on -Thames).

THE only way you can decrease the boreof the discharge pipe without decreasing

the capacity of the machine is to reduce thelength of the pipe to a point where itsresistance is equal to that of the existingain. diameter piping. You will also requirea fitting reducing gradually from tin. diameterto in. diameter in order to reduce frictionallosses to a minimum. The only way toincrease the delivery pressure is to increasethe fan speed-i.e., the pressure varies as thesquare of the fan speed. It must, in so doing,be remembered that the horse -power required

Readers are asked to note that we havediscontinued our electrical query service.Replies that appear in these pages fromtime to time are old ones and are pub-lished as being of general interest. Willreaders requiring information on othersubject; please be as brief as possible

with their enquiries.

will also be increased, i.e., the power requiredto drive the fan varies as the cube of thefan speed.

The pressure quoted will be insufficient forthe average commercial spray -gun, and it isconsidered that it is also too low for blowpipeoperation if a high flame temperature isrequired. The design and construction of an

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The above blue -prints are obtainable, post free,from Messrs. George Newnes, Ltd., Tower House,

Southampton Street, Strand, W.C.2.An * denotes constructional details are available free

with the blue -prints.

efficient blowpipe is specialist work and itis suggested that a blowpipe is purchasedfrom a reputable manufacturer.

Chlorophyll from GrassT AM at present producing dried grassI in commercial quantities. Pleasegive me an outline of method for pro-ducing chlorophyll from same. -H. A.Taggart (Belfast).

WE suggest that you " kill " the grass,prior to drying, by immersion in a vat

of boiling water. Drain superfluous liquor byspreading on racks, and then extract by meansof industrial spirit (ethyl alcohol). Thealcohol extract of chlorophyll is_then distilledfrom a steam -jacketed still, the alcohol beingthus recovered, while the chlorophyll remainsbehind.

We would suggest experimenting on thelaboratory scale first, for you may find itunnecessary first to partially dry the boilingwater extract -possibly pressing would suffice.

Moulding KaolinT HAVE 2 cwt. of powdered kaolin.I Can you please give me a formulausing this kaolin to produce a granite -hard product suitable for tiles or forcasting ?-Evan J. Thomas (Aberayron).

THE kaolin must be thoroughly pugged withwater into a soft paste of such con-

sistency that, when a piece about 2.1.11. diameteris squeezed tightly in the hand, it will repro-duce the fine lines of the skin. If paste is toohard, add a little water and re -pug. A woodetrmould, preferably of teak, must be made,shod on top and bottom edges with steelstrips about r/ 6in. thick. The thickness ofthe mould should be that of the tile. Lubricatemould with water (slop moulding) or withsand (sand moulding). Next pick up aquantity of paste from the mass, " bump "it on the previously sanded or watered bench,turn it and bump it five times, and then by ataut steel wire in a frame slice the mass into" clots " a little longer than the tile and aboutgin. thick. Dip the empty mould into wateror sand and then place it on the bench whichhas been similarly treated. Lift a clot fromthe pile, and after throwing it forcibly intothe mould, compress it and fill up the edgesand corners by a series of blows or puncheswith the hands. Surplus paste is removed bydrawing a wetted piece of wood over it.Drying -off can be done slowly in an open shed,the tiles being stacked in chequer work to aidventilation. This can be done only in summermonths. For quick drying and hardening,artificial heat must be provided or arrange-ments made to borrow the use of a kiln atsome school of pottery.

Electrodeposition QueriesRECENTLY I saw in Practical Mech-

anics an article dealing with copperdeposition on non-conductive materials.I should like more information on thefollowing points.

What type of transformer is necessaryfor 230 volts 5o cycles A.C. input to givex.2 volts, variable amperage from 6-40amps D.C. output ? What firms wouldundertake to build this ? Is it possibleto build this transformer from ex -government parts ?

When dealing with a number of articleswhat is the best method of making con-tact ? Could I put them on copper plateor hook them to a bar as a negativecathode ?

When using plaster forms what is thebest method of contact to the graphitefilm, also what other conductive coatingscan be used and where can they bepurchased ?-A. Heywood (Ashton -under-Lyne).


350

PROBABLYthe cheapest method of

obtaining 6 to 40 amps at i to 2 voltswould be by means of a car battery. Youmay be able to obtain quite cheaply an old carbattery which has one or two defective cells ;one 2 -volt cell, or preferably two or moreconnected in parallel, would be suitable foryour purpose. The battery could be chargedlocally or by means of a battery chargerconsisting of a step-down transformer andmetal rectifier, and quite a low charging currentcould be used.

Another method of obtaining a supply of6 to 4o amps at I to 2 volts is by means ofa motor -generator set consisting of a mainsvoltage motor which drives a small D.C.dynamo, the voltage output being controlledby a variable resistance in the field circuit ofthe dynamo. Another method would be touse a rotary converter. However, suchapparatus is likely to be rather expensive.Alternatively, you could use a step-downtransformer to supply a metal rectifier havingthe required output. Messrs. Galpins adver-tise a transformer having an output of 50-70amps at 2 to TO volts, or we could supplyconstructional details for a transformer ifrequired. A metal rectifier could be obtainedfrom one of the following firms :

Standard Telephones and Cables, Ltd.,Connaught House, Aldwych, London, W.C.2.Crypton Equipment, Ltd., Bristol Road,Bridgwater. Westinghouse Brake and SignalCo., Ltd., 82, York Way, London, N.T.Partridge Wilson and Co., Ltd., DavensetElectrical Works, Leicester.

You could either suspend the article orrest it on three contact points on a wireframe, not a plate, connected to the terminalof the vat. A preliminary coating which youmay find useful consists of a hot mixture of onepart of paraffin wax, two parts of beeswax,and two parts of powdered graphite, thesebeing melted and mixed together and after-wards evenly applied to the article. When thecoating has become quite cold a little powderedgraphite should be sprinkled on the surfaceand brushed vigorously with a soft brush.However, this method should not be used onarticles which will afterwards be washed inhot water or the wax may be melted arid thecoating stripped off.

Large's Storm GlassT HAVE a barometer which is called aI. Large's Storm Glass. It is composedof a glass tube Lin. diameter and 5in.long, sealed at both ends, and contains aliquid and some sort of crystals insuspension.

When the weather is to be fine thecrystals remain at the bottom of the tubeand when rain is imminent the crystalsrise to the top.

Could you give me some indication asto what the liquid is ; what the crystalsare and method of construction ?-N. Mather (Coventry).

THEREare several formulae for themixture contained in a Large's Storm

Glass, but all contain the same materials :120Z. flake camphor, 3oz. muriate ofammonia, 3oz. nitrate of potash, 21, pintsalcohol, 2 pints distilled water.

A suitable amount of this mixture is placedwithin the glass tube and the end scaled byheat. It is not under vacuum.

Anti fungusCreosoteT WISH to increase the anti -fungus1 properties of ordinary commercialgrade creosote. It is to be used on floors,joists, etc., of a bungalow badly affectedby the floods at Canvey. Can you helpme, please ?-T. Young (Isleworth).

YOU can adopt either of the suggestionsgiven below :

(I) Copper naphthenate is soluble in

NEWNES PRACTICAL MECHANICS May, 1953

creosote and can be applied to floors, joists,etc., in a single application.

(2) You can use the commercial gradecreosote and when dry wash over all surfaceswith a 4 per cent. solution of sodium fluoride.This substance is an excellent fungicide.You must remember that it is poisonous andetches glass, so the mixture should be madeup in a pail. The chemical can be obtainedfrom Vicsons, Ltd., 148, Pinner Road,Harrow, Middx.

Artist's Enlarger/ReducerCOULD you give me some information

on building the type of photographicapparatus used by artists for reducingor enlarging the image of a photographfor the purpose of line drawing ? Ibelieve this is something like a cameraobscura, and throws an image of thephotograph on to a ground glass screen.Alternatively, I could make a line tracingof the photograph which could be placedin the apparatus and projected on tothe drawing -board in the dimensionrequired, the instrument being arrangedto slide on a horizontal rod as shown inthe accompanying sketch.

I have a spare 5in. f4.5 lens previouslyused in an enlarger and am wonderingif this would be suitable.-G. Hodges(Essex).

FOR projecting a tracing made from aphotograph the best scheme would be

to place the drawing -board horizontally on atable, and the box carrying the lens, tracingslide and lamp vertically above it. The boxcould then be supported upon three detach-able legs, as shown in Fig. I.

Fig. 2 shows the manner in which theactual photographic image can he projecteddown on to the drawing -board.

Providing the angle of the 5in. f4.5 lensis wide enough, there is no apparent reasonwhy this should not be used. It is certainlyworth trying out.

You will have to pro-vide adequate ventila-tion for the lamp orlamps.

Fig. t.

InformationSought

Readers are invited to supply the requiredinformation to answer the following queries.

" Socredes," of Glasgow, asks : Couldyou give me some up-to-date information onthe subject of " shaded poles " in electricmotors ?

I understand this consists of some slightmodification to the pole face.

What form does the modification take ?Is such a modification possible on a per-

manent magnet, and if so, what effect mightit be expected to produce ?

Mr. F. E. Siggers, of Ceylon, asks :Have you at any time published a construc-tional article on exhaust -operated three-, four -or five -note horns for fitting to a car, please ?Can you give me enough information tomake one ?

Mr. H. Comber, Ireland, writes : I wishto make a mixer to handle ice-cream mixes offrom two to four gallons. My idea is to fit anextension to the shaft of a motor and invertthe gadget into a large can.

(I) What horsepower and speed would themotor need to be ?

(2) How should I loin the extension to themotor shaft ?

(3) Would the shaft need support other thanthat given by motor -bearings ?

(4) Would a thrust bearing be necessaryon the motor ?

Mr. R. Hamblin, of Watford, sends thefollowing query. I wish to construct a plugsand -blasting unit. I have a compressor, alsoa lathe.

Please tell me how to set about it.

Mr. J. B. Ball, of Morecambe, writes :Will you please tell me how to make a revolv-ing lampshade which uses the convectioncurrents produced by the heat from anelectric lamp ?

Suspension and sliding rod

Lens in focusing colla,

f

Drawingboard

Lens adjustable for focus andLegs adjustable for height

Hot air ventsPhotograph

Glass to keepheat outside box

Legs (3)(telescopic)

Drawing

Artist's enlarger/reducer apparatus

Slide holding-- tracing

Lamps



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One of these courses will lead to your advancementAccountancy ExamsAuditingBook-keepingCommercial ArithmeticCostingModern Business Methods

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GENERAL CERTIFICATE OF EDUCATION : R.S.A. EXAMS.


352 NEWNES PRACTICAL MECHANICS

m,n7r7riemr1.1

May, 1953

:am

IINSTITUTES

EXPERIMENTAL KIT

LEARN THE PRACTICAL WAYA specially prepared set of radio parts from which we teachyou, in your own home, the working of fundamentalelectronic circuits and bring you easily to the point whenyou can construct and service a radio set. Whether youare a student for an examination, starting a new hobby,intent upon a career in industry, or running your ownbusiness -this Course is intended for YOU -and may beyours at a very moderate cost. Available on Easy Terms.WE TEACH YOU: Basic Electronic Circuits (Amplifiers,Oscillators, Power Units, etc.) Complete Radio ReceiverTesting & Servicing.

POST IMMEDIATELY FOR FREE DETAILS

TO: E.M.I. INSTITUTES, Dept. 144 XGrove Park Road, Chiswick, London, W.4

Name

Address

*Experimental Kits alsoform part of the follow.ing courses : Draughts-manship, Carpentry,Chemistry, Photography,Commercial Art, Etc.

INSTITUTESAssociated with

COLUMBIA &

MARCONIPHONE uMV

(His Master's Voice)

I . C. I 2

SPARKS'DATA SHEETSare the Safest, Simplest and FinestConstructional Sheets of Guaranteed

and Tested Radio Designs.

SPECIALANNOUNCEMENT

INTRODUCINGA NEW

SERIESTHE

" M/S" SERIES OF AMPLIFIERSI am happy to be able to announce that thecircuits contained in the booklet, " TheAmateur's Guide to Valve Selection"(published by Messrs. Mallard, Ltd.), ARENOW AVAILABLE, through k led permissionof

MESSRS. MULLARD LTD.in my usual

SPARKS' DATA SHEET Form.THIS UNIQUE INNOVATION places for thefirst time in the history of the RadioAmateur, a combination available to everyConstructor which surpasses anything yetoffered -

THE FINEST VALVE TECHNI-CAL SKILL PLUS THE FINEST

PRACTICAL DATA SHEET.

Send 214. stamp for my latest List whichgives full details of the above, and the27 other tested and guaranteed designs.

It L. ORMOND SPARKS (M)48A, HIGH ST., SWANAGE, DORSET

4etwate wimpyof a Once

Precision built with watch -like accuracy.neat, light and strong. records up to10,000 miles and then repeats. Completewith striker and rust -proof hub spindlebracket. Chromium placed finish.

Price 7/6.

ciae Road's CYCLOMETERJOSEPH LUCAS (CYCLE ACCESSORIES) LTD CHESTER ST BIRMINGHAM 6

HIGHSTONE UTILITIESSoldering Irons. -Our new streamlinediron is fitted with a pencil bit, 200/250v.50 watts, 11/8. Standard Iron with adjust-able bit, 200,250 v. 60 watts, 13/6. IleavYDuty Iron, 150 watts, 16/6, all post 6dMeters. -15 v., 2iin., m/c., 9/6 ; 150 v.Sin., m/c., 10/- : 3.5 amp. 2in.. T.C. (P-S amp., 21in.. T.C.. in case with switch, 9/6101 m/A, 21n.. mle.. 7/6 : Meter MovementsUnits with 2-5011 microamps 7/., post 1/-.Bell Transformers.- These' guaranteedtransformers work from any A.C. Mains,giving 3, 5 or 8 volts output at I amp..operate bulb. buzzer or bell. Will supplylight in bedroom or larder. etc., 9/-. SimilarTransformer but output of 4, 8 or 12 volts.12/6. Both post 8d. BELLS for use witheither the above or batteries, 6/- poet 6d.BUZZERS. 3/9, or Heavy Duty, 4/6. post 5d.Ex.R.A.F. 2 -valve (2 volt) MicrophoneAmplifiers, as used in 'plane inter -corn.,in self-contained metal case ; can bo usedto make up a deaf aid outfit, Intercom-munication system, or with crystal setcomplete with valves and Fitting instruc-tions. 20-, post 2/-. Useful wooden boxwith partitions to hold amplifier, 21- extra.Ditto. less valves. 10,-. One valve ampli-fier, complete with valve. 10/6, post 1/6.Hand Microphones, with switch in handle,and lead. 4/6. Tammy. 6!-. Similar lnstrumeat, moving coil, 7/6. All post 9d.Mike Buttons (carbon), 2/-. Moving Coil.4/6. Transformers, 5/.. All post 4d. each.Sparking Plug Neon Testers, with vest-pocket clip, 3:3, or with gauge, 3/8, post 3d.S.B.C. Neon Indicator Lamps, for use onmains to show ' live " side of switches, etc3/6, post 4d. Neon Indicator, completewith condenser, pencil type with vest-pocketclip. 7/6, Post 5.1.Crystal Sets. Our latest model is a realradio receiver, fitted with a permanentcrystal detector. Have a set in your ownroom, 12/8. poet 8d. De Luxe Receiver. Inpolished oak cabinet, 19/6. post SparePermanent Detectors, 2/- each. Whenordered separately, 2/6 : with clips andscrews, 2/10. post 3d. headphones, brandnew, S.G. Brown. G.E.C., etc., 15.-, 23/- andsuper -sensitive, 30/- a pair, post Sd. NewHeadphones, 10/- a pair. Balanced arma-ture type (very sensitive). 12/6 a pair.Both post 8d. New Single Earpleees,3/6. Bal. armature type, 4/6 ex R.A.F.earpiece. 2/6, post 4d. headphones, ingood order, 61- (better quality, 7/6). allpost 9d. (All Headphones listed aresuitable for use with our Crystal Sets.)Money refunded if not completely satisfied.

HIGHSTONE UTILITIES58, NEW WANSTEAD, LONDON, Eat.New illustrated List sent on request withlid. stamp and S.A.E. Letters only.


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ELECTROPLATING AT HOME - WorldRadioHistory.Com...were a modern invention. The fact is that from the earliest days of the cinema-tograph there have been literally dozens of inventions