SMALL-GROUP STUDYIN A NORMALLY LIT ROOM

The image is cast upon a screen in thedark-chamber turret at table height. Eachobserver (up to 10) has a separate light-excluding viewing hood. The pathologisthere is discussing a slide with the surgeon;the unused hoods are easily shuttered off.

LARGE-GROUP EXHIBITIONIN THE DARKENED AUDITORIUM

So intense is the Scopicon light source thatImages up to ten feet across can be pro-jected. Through a system of auxiliary lensesthe operator can follow a biological speci-men through a progressive series of ever-closer localizations, up to ultimate demon-stration under oil-immersed objectives.

a or10orlOOoQuickly adaptable to viewing on any scale, the mobileScopicon couples convenience with efficiency. Its high-pressure mercury arc is the brightest light source everemployed for microprojection. The focal spot is only1 mm square (approx.). Its pinpoint character permitsflickerless projection of sharply detailed images up toten feet across even under oil-immersed microscopeobjectives. Let us send you the brochure describing thisremarkable instrument.

micromprojectionl equipmentSCOPICON, Inc. 215 E. 149 ST. NEW YORK 51 I

"Detailed reading and use have served to strengthen my beliefthat it is the best teaching text in the field of Comparative Anat-omy that I have encountered in twenty years of experience."Professor lWillianm A. Campbell, College of the Holy Cross

Have you looked at a copy lately?

THE VERTEBRATE BODY. By ALFRED S. RONIER, Alexander Agassiz Professorof Zoology and Director, Museum of Comparative Zoology, Harvard University.643 pages, 6" x 9", with 987 illustrations on 363 figures. $6.00.

W. B. SAUNDERS COMPANYWest Washington Square Philadelphia 5

February 8, 1952 1

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NO ZERO ADJUSTMENTCONVENIENT SMALL SIZE 5x71A4x13 IN.LIGHT IN WEIGHT-ONLY 111/2 POUNDS~~~~~~~~~~~~~~~~~A__The SPECIAL FEATURES OF THE DENSICHRON qualify it for use in many light-measuring operations in scientific research and industrial process control. Some of the labora-tory applications for which the DENSICHRON is particularly well adapted are-

PHOTOMICROGRAPHYCHROMATOGRAPHY*

REFLECTOMETRY

MICRODENSITOMETRY

COLORIMETRY* See "Quantitative Paper Chromatography for Students" by Patton, A. R., Jr. Chem. Educ., 28, 629 (1951)

The DENSICHRON is supplied complete with a blue-sensitive light probe (or red if specified),five measuring apertures, a cone with I/8 inch aperature, and metal support for the probe unit.The current consumption is 30 watts. For operation on 115 volts-60 cycle AC only-

WRITE FOR 12-PAGE BOOKLET GIVING OPERATION CURVES, RESULTS EACHOF LABORATORY TESTS AND OTHER VALUABLE INFORMATION. $225.000

Reflection Unit Accessory with Voltage Regulated Transformer-$75.00

SCIENCE, Vo1. 115

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h.ase contrastequipment

...gives you finger-tip control-at lower cost

With Leitz Phase Contrast Equip-ment, you make a continuoustransition from "brightfield" to"phase contrast" to "darkfield"simply by adjusting the height ofthe mirror body in the condenser.There is no cumbersome substageapparatus, no interruption of ob-servation to unscrew and replaceobjectives. The construction of thespecial condenser, after Heine,allows maximum resolution withboth achromatic and newlydesigned apochromatic objectives.This sweeping versatility eliminatesthe need for numerous specialobjectives. Consequently, yourLeitz equipment, which covers thecomplete range of contrast, willcost you under $900. Compare,and seethe difference,in economy,versatility and ease of operation.

(1) Special Condenser after Heine with rack andpinion (Tr) for adjustment in height ofmirror body (Sk); supplied with Screw-OnImmersion Cap (la); centering screws (S)

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Pv 10/0.25(3) Achromatic Dry Objective Pv 20/0.45(4) Apochromatic Dry Objective Pv Apo 40/0.70

with cover glass correction mount andautomatic sharpness compensation

(5) Apochromatic Oil Immersion ObjectivePv Apo Oil 90/1.10

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SCIENCE, Vol. 1154

c"This is a remarkable book,

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MAN ON HIS NATURE is a famous biologist'sfearless and invigorating philosophy con-

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achievement, like a great fresco, a grand sym-phony, or an heroic poem or drama.'"4 SirCharles's astonishing accounts of some of theprocesses of nature in living organisms are lyri-cal testimony to a man's continual wonder andquestion before the processes he is investigating.Here is a small excerpt:

The child's eye is not only an eye true to thehuman type, but an eye with personal likenessto its individual parent's. The many cells whichmade it have executed correctly a multitudinousdance engaging millions of performers in hun-dreds of sequences of particular different steps,differing for each performer according to hispart. To picture the complexity and precisionbeggars any imagery I have. But it may help usto think further."MAN ON His NATURE was selected as one of

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ISCIENCE, Vol. 114

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SCIENCE, Vol. 1158