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TOLMAN

Theory and Practice

Theory of the Relativity

of Motion With Appendix

MILLIKAN: Mechanics,
Molecular Physics, and Heat.
MILLIKAN and MILLS:
Electricity, Sound, and Light.

A supplement to this work, written by the
author, has just been issued. Under the
title,
Relativity Theories in Physics
this Appendix gives a general description
of the nature of relativity theories, to-
gether with brief discussions of Tolman's
theory of similitude or relativity of size,
of Einstein's theory, of the relativity of
uniform motion, and of Einstein's theory
of gravity and general relativity.
ix + 242 pages (including Appendix).
Cloth, $1.75. Carriage extra. Weight,
154 pounds.

Appendix only (paper), 25 cents.
The University of California Press

BERKELEY, CALIFORNIA

These books provide for intimate correlation between classroom discussion and laboratory exercises. Together they constitute an up-to-date full - year course,

GINN AND COMPANY Boston New York Chicago London Atlanta Dallas Columbus San Francisco

A NEW WILEY BOOK

Principles of Radio Communication

T

By J. H. MORECROFT
Associate Professor of Electrical Engineering, Columbia University

Assisted by A. PINTO and W. A. CURRY
\HIS BOOK deals with all phases of the Radio Art, going completely into

both theory and operation. The treatment is more thorough than is generally

given, and for this reason the book will have a wide appeal among workers in this field, the importance of which is so rapidly increasing.

The text of "RADIO COMMUNICATION” comprises 935 pages, 6 by 9 inches, and contains 788 illustrations, many of which are reproductions of oscillographic records of transient phenomena. All curves used to illustrate formulæ are carefully executed to scale and may be used as typical problems. The book is cloth-bound. $7.50 postpaid.

Enter Your Order for a FREE EXAMINATION Copy

JOHN WILEY & SONS, Inc.

,

432 Fourth Avenue

NEW YORK

PHYSICAL METHODS IN

LABORATORY ANALYSIS

It is a well-known fact that any measurement in any science involves the application of a physical method. The measurement may be mechanical, as with an analytical balance or a kymograph; it may be one of temperature or heat, as with a respiration calorimeter; it may be optical, as with a microscope, spectroscope or colorimeter; or it may be electrical, as of resistance, current or potential difference, any of which may have a definite, known relation to some biological characteristic that is being investigated.

Leeds & Northrup Company has long specialized in electrical measuring instruments and their applications. A recent activity has been the development of suitable instruments for measuring the potentials of a hydrogen electrode, in solutions and media, which correspond to hydrogen-ion concentrations or pH values.

The studies we have made on this subject are summarized in Catalogue S75, which gives a clear explanation of the principles involved in the measurements and describes how they are made. It also contains a representative bibliography of fifty titles, bearing on many scientific applications of the hydrogen electrode, and a descriptive price list of suitable electrometric apparatus. If you feel that the publication might be of service in your laboratory, we should be very glad to send you a copy gratis.

Leeds & Northrup Company

Electrical Measuring Instruments 4901 Stenton Ave.

Philadelphia, Pa.

SCIENCE

A Weekly Journal devoted to the Advancement of Science, publishing the official notices and proceedings of the American Association for

the Advancement of Science

Published every Friday by
THE SCIENCE PRESS
LANCASTER, PA.

GARRISON, N. Y.
NEW YORK, N. Y.

Entered in the post-office at Lancaster, Pa as second-class

matter, under the act of March 3, 1879

The University of Adelaide

Applications are invited for the position of Professor of Zoology in the university of Adelaide, South Australia.

The Professor will be required to offer a course of Lectures and Practical Work in Elementary Animal Biology, suitable for students of Science, Medicine and Agriculture, together with an advanced course in Zoology for students in Science. A demonstrator and a collector will be provided. Salary, £1,100 per annum.

Applications with testimonials, statement of academic qualifications, experience, copies of publications, and a recent photograph, should be forwarded to the Registrar, The University of Ade. laide, South Australia, to reach him not later than August 1st, 1921.

Candidates must indicate the earliest date at which they can commence duties. Further information may be obtained from: (a) The Agent-General for South Australia,

Australia House. Strand, London. (b) The Commissioner for Australia, 61 Broad

way 3012, New York City, U. S. A. (c) Any University in Australia or New Zea

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THE COCCIDAE

SCIENCE PROFESSORS WANTED Tables for the Identification of the Subfamilies and Some of the More Important Genera

Applications are invited for vacant and Species Together with Discussions of Their Anatomy and Life History positions in Physics, Biology, and Modern

By
ALEX. D. MacGILLIVRAY Ph.D.

Languages at Mount Allison University, Prof. of Systematic Entomology in the University of Nlinois

Chapters devoted to near relatives of Coccids, Prep- Sackville, New Brunswick, Canada. aration, External Anatomy, Classification, and to each of the Subfamilies and Tribes, Twenty-seven in all.

Apply to 8vo. Cloth. IX+502. $6.00 net. Sent prepaid upon receipt of price. Order direct from publisher

B. C. BORDEN, President SCARAB COMPANY 603 Michigan Ave.

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The Philippine Journal of

Science

Publications of Carnegie Institution of Washington

Published by the Bureau of Science of the Govern

ment of the Philippine Islands

A monthly periodical devoted to the scientific and

commercial interest of ths Tropics

The Journal is now being issued monthly; the former sections are discontinued. The January, 1920, number begins Volume 16. Subscription price, $5.00 per year.

A list of the publications of the Philippine Bureau of Science and a sample copy of the Philippine Journal of Science will be sent upon request.

No. 280. Benedict, F, G., W. R. Milen, Paul Roth

and H. Monmouth Smith, Human Vitality and Efficiency under Prolonged Restricted Diet. Octavo, xi + 701 pages, 124 figures.

Price, $9.00. No. 302. Benedict, F. G. and F. B. Talbot.

Metabolism and Growth from Birth to
Puberty. Octavo, vi + 213

pages, 55 figures.

Price, $2.00. No. 216. Carpenter, T. M. A Comparison of

Methods for Determining the Respiratory Exchange of Man. Octavo, 265

pages, 74 figures... ..Price, $2.50. No. 303. Carpenter, Thorne M. Tables, Factors,

and Formulas for Computing Respiratory Exchange and Biological Transformations of Energy. Will be issued

by May 1. Octavo. No. 279. Harris, J. A. and F. G. Benedict. А

Biometric Study of Basal Metabolism in Man. Octavo, vi+ 266 pages, 30 diagrams.

...Price, $4.00 No. 309. Smith, H. Monmouth, Gaseous Ex

change and Physiological Requirements for Level and Grade Walking. Octavo..

...In Press The publications of the Institution pow number over 400 volumes, the subjects including Anatomy, Archæology, A8tronomy, Botany, Chemistry, Climatology, Economics and Sociology, Embryology, Experimental Evolution and Heredity, Engineering, Folk-Lore, Geology,. History, International Law, Literature, Mathematics, Medicine, Nutrition, Paleontology, Philology, Physics, Stereochemistry, Terrestrial Magnetism, Zoology. Classified and descriptive lists will be sent postpaid on application.

All communications sbould be addressed to CARNEGIE INSTITUTION OF WASHINGTON

WASHINGTON, D. C.

Subscriptions and orders for publications should be

sent to

THE BUSINESS MANAGER

Philippine Journal of Science Bureau of Science

MANILA, P. I.

Anco Biological Supplies

When in the market for any

LIVING MATERIALS

GLASSWARE THERMOMETERS

Frog Eggs, assorted stages, per dozen, $0.25 Trichina in Muscle . per culture, 5.00

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Write for Catalogue No. 21

LABORATORY

APPARATUS

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INSTRUMENTS

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La Motte Indicator Field Set

for Determining Acidity and

Alkalinity of Soils As used in studies described by E. T. Wherry. Jour. Wash. Acad. Sci., April, 1920, and Rhodora 13-1920.

Pocket size case containing six Indicator solutions (PH 3.0 to 0.8) convenient for carrying into the field. Full instructlons accompany cach set.

PRICE, $2.85 COMPLETE

Made and sold by LAMOTTE CHEMICAL PRODUCTS COMPANY 13 WEST SARATOGA ST., BALTIMORE, MARYLAND

for Colleges or Universities

Scientific Utilities Co., Inc.

Manufacturers, Importers, Exporters 18 East 6th Street

NEW YORK, N. Y.

ANNOUNCEMENT

WE are greatly pleased to be able to announce to the readers of Science

and to all users of scientific apparatus and instruments in general that we have recently secured the services of

DR. PAUL E. KLOPSTEG who has already entered upon his duties as Technical Supervisor of Development and Manufacturing.

While a student at the University of Minnesota, from which he received his Ph.D. degree in 1916, Dr. Klopsteg devoted particular attention to the study of electrical measuring instruments. He served on the instructional staff of that institution for several years as assistant in the departments of Electrical Engineering and Physics, and was later promoted to the rank of Assistant Professor of Physics. In 1917 he entered the Government service, spending a year as Electrical Engineer in the Ordnance Department, during which time he aided in the development of the Aberdeen Chronograph for the measurement of projectile velocities. In the fall of 1918, as a result of his work upon this instrument, Dr. Klopsteg became identified with Leeds and Northrup, who had undertaken its manufacture. Later his activities were centered in the Sales and Advertising Department, where he has been largely responsible for the collection and preparation of technical and scientific information upon instruments and methods.

Since the organization of the Central Scientific Company it has been our ambition to produce the BEST apparatus in design, workmanship, finish, durability and adaptability to the purpose for which intended, in whatever field of trade demands might lead.

When our business was almost entirely that of a High School Supply House, we strove to realize this ambition, adding from time to time to the personnel of the organization men who were thoroughly familiar with this field and who could be trusted to intelligently guide our efforts. When the demands led us later into the field of College Physics and of Industrial and Engineering Chemistry, further additions were made to the organization so that we might be equipped to render intelligent and accurate service to users of apparatus in these fields.

The European War having cut us off from former sources of supply, our Manufacturing Department was called upon to develop almost at once the manufacture of numerous physical and chemical instruments for which there was most urgent demand. Again additions were made to both engineering and manufacturing divisions of men whose training would enable us quickly and accurately to develop these instruments.

With the coordination of the technical efforts of these various groups under the supervision of Dr. Klopsteg, we believe that we are in a position to render a service to users of scientific apparatus which will justify our ambition to make the name “ CENCO » stand always and only for that which is best. As we have always been ready in the past to place upon our apparatus a guarantee of complete satisfaction, backed up in case of doubt by immediate replacement or full credit, we now repeat this guarantee with the additional promise that whether it be a simple piece of high school physical apparatus, a piece of chemical glassware, an ordinary quantitative laboratory device, or a precise measuring instrument, the name CENCO upon it will stand as evidence that the need which it serves has been carefully analyzed, the piece has been scientifically designed to meet this need, has been carefully made of the proper materials to fulfill its purpose and has met the most rigid test of its fitness when completed. This is our promise.

CENTRAL, SGIENTIFIG COMPANY
LABORATORY mece

SUPPLIES
Apparatur

CENCO

Chemicals 460 E.Ohio St.,

UN.A

Chicago

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