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,

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A NEW WILEY BOOK

Principles of Radio Communication

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

Assisted by A. PINTO and W. A. CURRY
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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.

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JOHN WILEY & SONS, Inc.

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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

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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.

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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
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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.

Urbana, Illinois

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