TOLMAN Theory of the Relativity of Motion With Appendix 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, together 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, 1 pounds. Appendix only (paper), 25 cents. The University of California Press BERKELEY, CALIFORNIA NEWARK, N. J. How Intense Is Sunlight Its intensity, of course, depends upon latitude, season, time of day, atmospheric conditions; but whatever it happens to be, it can be measured readily with Leeds & Northrup Company's MACBETH ILLUMINOMETER Illumination of any intensity, artificial or natural, is within the range of this useful instrument. Its scale reads foot-candles directly. It is provided with a reference standard lamp with which each observer standardizes the instrument according to his own visual perception. This is done wherever he happens to be-no photometric dark room is required. The illustration shows one method for making a measurement. The illumination on the test-plate, mounted on a tripod, is being measured. A translucent plate, mounted in a "horn", can be fitted to the instrument, and by pointing the "horn", in any direction, up, down or sidewise, the illumination due to the light from that direction is measured. The Macbeth Illuminometer is especially suited for investigations concerned with the reactions of liv ing organisms to light. Hydrogen Ion Indicators SORENSEN'S LIST Sorensen in an extensive investigation of the correspondence between colorimetric and electrometric determinations of hydrogen ion concentrations revealed discrepancies which are attributed mainly to the influence of protein and salts. He chose those indicators which were relatively free from the socalled protein and salt errors. Sorensen's final selection, together with Ph range of each indicator, is given below. By specifying National Stains and Indicators, you are assured of receiving dyestuffs manufactured under expert supervision and subjected, prior to sale, to the most rigid chemical and biological tests known. Catalogue upon request. National Stain and Reagent Co. Long years of experience and continuous factory operation, coupled with fortunate climatic and physical conditions, have enabled the Munktell Factory, at Grycksbo, Sweden, to supply the Chemists of the world with an unequalled product. Aside from the chemical constitution of the paper, which can, of course, be controlled by the laboratory of the factory, other constituent features can only be attained by expert hand manipulations, as, for instance, the weight, texture and uniformity, for it must be remembered that all chemists' Filter Paper must from its very character be hand made. Transient help or workmen trained in other lines of paper manufacture, especially those who have worked in factories where paper is made by machinery, can not be of much use, For generations the sons and daughters of the workmen in this factory have succeeded their parents and the same is true at this date. In this way the necessary "touch" has been developed in these workers from their childhood on. As the chemical industries have developed so also has this factory enlarged its line so that at the present time, as sole United States Agents, we are able to offer from stock for prompt shipment a grade of Munktell's Chemists' Filter Paper to meet any known requirement. Descriptive pamphlet, showing price and full particulars, sent upon applicaton. Samples of paper furnished on request. E. H. SARGENT & CO. IMPORTERS, MAKERS AND DEALERS IN CHEMICALS 155-165 EAST SUPERIOR STREET CHICAGO, ILL. |