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Yale University

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Marine Biological Laboratory

Woods Hole, Mass. INVESTIGATION Facilities for research in Zoology,

Embryology, Physiology, and BotEatir. Year

any. Eighty-four private laboratories, $100 each for not over three months. Thirty tables are available for beginners in research who desire to work under the direction of members of the staff. The fee

for such a table is $50.00. INSTRUCTION

Courses of laboratory instruction

with lectures are offered in InverteJune 29 to August 9

brate Zoology, Protozoology, Em

bryology, Physiology and Morph1921

ology and Taxonomy of the Algae. Each course requires the full time of the student. Fee, $75. A lecture course on the Philosophical Aspects of Biology and Allied Sciences is

also offered. SUPPLY Animals and plants, preserved, livDEPARTMENT

ing, and in embryonic stages. 'Pre

served material of all types of Open the Entire Year

animals and of Algae, Fungi, Liverworts and Mosses furnished for classwork, or for the museum. Living material furnished in season as ordered. Microscopic slides in Zoology, Botany, Histology, Bac. teriology. Price lists of Zoological and Botanical material and Micro scopic Slides sent on application. State which is desired. For price lists and all information regarding

material, address GEO.M. GRAY, Curator, Woods Hole, Masi The annual announcement will be sent on application to The Director, Marine Biological Laboratory, Woods Hole, Mass.

SCHOOL OF MEDICINE Affiliated with the New Haven Hospital and New Haven Dispensary

109th Session Reorganized on a full-time basis Entrance Requirements : A minimum

of two years (or its equivalent) of college including general biology, physics, general and organic chemistry, physical chemistry or laboratory physics, and either French or German. ALL OF THE GENERAL FACILITIES OF THE UNIVERSITY ARE AVAIL.

ABLE TO MEDICAL STUDENTS As the number admitted to each class is limited, applications must be made before July 1. Dean, Yale University School

of Medicine NEW HAVEN, CONN.

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Dopt, of Natural Scionc.

G. Lagai, Ph.D.

404-410 W. 27th St

Now York City

Manufactured by The Thermo Electric Instrument Co. 8 Johnson Street

Newark, N. J.

CADMIUM STANDARD CELLS

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For use with potentiometer, electrometers, and ballistic pulvenometers, or wherever else a precision standard of electromotive force lo needed.

Negligible Temperature Coefficient.

Highly Constant E. M. F.
Contento bermetically sealed in glans that lowering of electro-
motive force due to evaporation is impossible.

Mounted in moulded box, or unmounted.
My comparison certificate accompanies each cell without charge
Bureau of Standards certifcate etn.

On November 13, 1916, three normal admium cells made by me were certified by the Bureau of Standards as differing from their group of reference cello by less than one part in one bundred thousand, all three having the ame value.

On March 30 1930, after the lapse of three years and four months, the same three cells were again compared by the Bureau of Standards. The maximum difference among the three was less than one part per hundred thousand, and the maximum difference from their certified value of 1916, was less than one part per bundred thousand.

In other words, these cells showed a degree of constancy to all intents equal to that considered most highly satisfactory, if not remark. able, in the very best type of precision resistance standards. (see Bul. Bur. of Stand. Vol. 3. No. 3. D. 437.)

The cells in question were in nowise special. They were made of the materials regularly prepared by me, and were set up with no greater care than that constantly employed in the making of my stan. dards.

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Marion Eppley,

AM, Ph.D.)
Physico-Chemical Apparatus.

NEWPORT, R. I.

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Natural History Material

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ZOOLOGY

MINERALOGY We have been handling Natural History Material of all kinds for the past fifty years, and so have accumulated a very complete stock. Our prices are as low as the quality of the specimens will permit. We are constantly preparing circulars and price lists covering our material in the

different branches,
which we will be pleased to send free of
charge to the readers of Science.
Some of our recent circulars :

S-121 Rare Bird Skins
S-122 Mounted Bird Skins
S-98 Material for Dissection
S-123 Philippine Land Shells
S-120 Special Minerals
S-110 Complete Trilobites
S-111 Jurassic Fossils

S-119 Cretaceous Fossils
CONCHOLOGY GEOLOGY

TUBULAR APPLICATORS
NEEDLE APPLICATORS - FLAT APPLICATORS

and
APPLICATORS of SPECIAL DESIGN
COMPLETE INSTALLATIONS SEMANATION APPARATUS

SOLD ON BASIS of U. S. BUREAU
of STANDARDS CERTIFICATE

CORRESPONDENCE INVITED BY OUR
PHYSICAL CHEMICAL and MEDICAL DEPARTMENTS

THE RADIUM COMPANY

OF COLORADO, INC

Ward's Natural Science

Establishment College Ave. Rochester, N. Y.

MAIN OFFICE REDUCTION VORO
DENVER, COLO. U. SA

BRANCH OFFICES
122 S. Michigan Ave, O UNION SQUARE

LONDON
CHICAGO
NEW YORK

PARIS

The Silverman Illuminator

A now eye for the microscope Offers important advantages for practically every application of the Microscope

-It shows more detail. & A clearer and better defined picture is presented to the eye and the camera. c-Several novel methods of illumination can be produced. d-!t saves very much valuable time.

-It prevents eye strain, eye fatigue, and brain fag. s-It can be lowered in to deep, hollow places. 6-It gives excellent results for very low power work as well as higher magnifi

cations, also in oil immersion work. 6-It can be used with any Microscope, ordinary or binocular.

A small circular tube lamp surrounds the objective and furnishes a diffused and uniform illumination directly where it is needed. The Silverman Illumi. nator marks

A Great Advance in Microscope Illumination

For sale by all the better dealers

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Write for

Bulletin 45-B

Ludwig Hommel & Co.

530-534 Fernando St,

PITTSBURGH, PA.

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Our Laboratory Spectrometers

Are sold in competition with instruments of European make

to many of the best laboratories throughout the world. WM. GAERTNER AND CO.

Physical and Astronomical Instruments 5345-49 Lake Park Avenue

CHICAGO

Eastman Organic Chemicals

DURING the past month the following chemicals have

become available:

1003 Anisolesulfonphthalein
1002 Benzoyl Auramine
1011 d-Borneol
996 * Chloral Alcoholate
999 * Dibenzylamine
1004 * p.p'-Dichloroazoxybenzene
1005 Ethylene Oxide

1016 * Ethyl Phenylbromoacetate 998 Glycollic Acid 992 * Beta-Naphthyl Salicylate 427 * 4-Nitro-2-aminotoluene 1000 * Resorcinol Monoacetate P1009 Sodium Indigodisulfonate 1015 * Tribenzylamine

Of the above list all those distinguished by an asterisk have been prepared or purified in our laboratory.

EASTMAN KODAK COMPANY
RESEARCH LABORATORY

Rochester, N. Y.

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Lee Surrenders to Grant Appomattox, April 9th, 1865From the People's Standard History of the U. S.

WHATMAN and

The Civil War DURING the Civil War the Confederate States

of America printed some of their currency on Whatman paper. Thus, the “South," quick to appreciate quality and true worth, added its endorsement to the famed list of Whatman users. With an historic background of proven supremacy, and sponsored by a century and a half of skill and experience, it is not surprising that

Are thoroughly satisfactory for scientific work, which accounts for their being used in so many of the educational and research laboratories throughout the United States.

If you are equipped, and after long service your “Chloride" battery needs some renewals; or if you contemplate a new installation we are ready to serve you.

By arrangement with the factory we act as Special College Representatives and are prepared to furnish portable or stationary outfits, with any nuinber of cells for current capacity from } ampere to any maximum desired.

May we send you catalog? To aid us in rendering good service, please state what your requirements are.

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JAMES G. BIDDLE

1211 ARCH STREET PHILADELPHIA

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