to all whom it may concern:

Be it known that I, NIKOLA TESLA, a citizen of the United States, residing at New York, in the County and State of New York, have invented certain new and useful Improvements in METHODS OP REMOVING GASEOUS MATTER FROM CLOSED RECEPTACLES, of which the following is a specification, reference being had to the drawings accompanying and forming a part of the same.

I have discovered that an electric current, directed under certain conditions into a sealed bulb, or in general, a closed receptacle, so as to exercise an influence upon the confined body of gaseous matter therein, -- as may be done by connecting a single electrode within the receptacle to one of the terminals, or two electrodes to the two terminals of a proper source respectively -- produces within the bulb or receptacle, a rarefaction of the gaseous matter, which may be carried to a degree far beyond any attained heretofore by the aid of the methods and apparatus used for his purpose.

Upon this discovery my present application is based.

In the practical operation of producing high vacuum I have employed the method and apparatus which I shall here in after more particularly refer to in connection with the drawing accompanying this application, and which my experiments and investigations have led me to adopt as the most effective for general purposes. The drawing is a diagram illustrating mainly, an apparatus for producing currents of high frequency and high potential which currents I have found most effective in the practical carrying out of discovery. This apparatus, in all essential respects, is one of my earlier inventions and is described more in detail than I deem to be necessary herein, in a patent granted to me June 23rd, 1891, No. 454,622.

A is an electrical generator such as an alternating current machine.

In the circuit of this sorce is a primary coil В which exerts its inductive effect upon a secondary coil С composed of longer and finer wire in order to raise the potential of the current impulses.

The secondary circuit, or that having the coil С as l ti source I includes the primary of second step—up transformer, which, preferably, comprises but a single turn or but a very small number of turns, and which I have designated by D.

Between the terminals of the coils С and D are interposed condenser E, and between these latter and the terminals of the coil С as shown at P, provision is made for producing a sudden or disruptive discharge in the circuit of coil D. The proper relations of self-induction capacity, periodicity and resistance, which are necessary to the maintainance in such a system of an oscillating or intermittent discharge are now well understood.

G is a secondary coil in inductive relation to the primary D and preferably wound inside of the same.

The terminal H, or that nearer the primary conductor D, is carried to ground, while the other terminal is led оff to the device which is to be exhausted.

As typical of the class of devices which it may be desirable to exhaust of their gaseous contents, I show a glass bulb or globe D, though I may here remark that I consider herein a receptacle of glass merely for convenience, as it may be composed in part or whole of other materials. Within this globe is an electrode M of aluminium or like conductor which is but slightly dissipated by electric action, and which is or may be directly supported by a conducting wire N passing through the wall of the receptacle.

Usually, by means of in ordinary vacuum pump to which the globe L is first attached, I exhaust the latter until upon the application of the current a glow of whitish light appears in the globe-which is indicative of a comparatively low vacuum. I then disconnect the globe from the pump and subject the residual gaseous matter therein to the action of the electrical currents produced in the apparatus shown, by cameo ting the electrode M to the free terminal of the secondary G of the transformer as indicated.

This action of the currents upon the gaseous matter within the globe when continued for a determinable period, produces Is globe the most perfect vacuum which can be or which, I believe, ever has been obtained, the most

noticeable outward evidences of this result being first, the disappearance of the white light characteristic of the comparatively low degree of exhaustion, followed by the appearance of brilliant phosphorescence or fluorescence on the walls of the globe, which phenomenon then gradually diminishes and eventually vanishes completely. The globe or receptacle, which during the first part of the above described operation, is usually heated to a considerable extent, rapidly cools down upon the disappearance of the phosphorescent or fluorescent effects, at which stage the process should be arrested, as otherwise, in such forms of device as I am now considering, I have noticed a tendency of a bright spark to form in the seal-off which is liable to injure the globe at that point.

I would state that heating the globe initially hastens the process of exhaustion.

In the extended investigations made by me, and by careful observation of the effects produced during the process above described I have been able to detect the actions which offer a satisfactory explanation of the phenomena, and which in general, accord with accepted theories on the subjects to which the discovery pertains. Without, however, advancing herein any theory which I may have adopted with regard to this phenomenon, since I do not regard this as essential to a proper understanding of the invention, I would merely state that by following the procedure I have described, the result will be attained.

It is essential, I believe, that the potential of the current used should be very high, but the frequency may be much lower than that which is normally produced by the apparatus illustrated. For example, an ordinary Induction coil may be used to produce the currents if it be constructed to develop a sufficiently high potential.

In many other obvious ways the character of the current source and that of the devices to be exhausted may be greatly varied. I have confined my description, for instance, to a receptacle containing but one electrode, and this is the most effective form when the frequency and potential of the source are sufficiently high. But two or more electrodes may be employed connected

to the same terminal or to the two terminals of a source of currents such as that described, or one possessing similar properties.