of a droplet under the influence of the field was in all cases a multiple of the difference of velocity associated with the electronic charge. Experiments were tried on thousands of drops in different media, some of the drops being made of nonconductors like oil, some of semiconductors like glycerin, some of excellent metallic conductors like mercury. In every case, the initial charge placed upon the drop by the frictional process, and all the dozen or more charges which resulted from the captur by the drop of ions, were found to be exact multiples of the smallest charge caught from the air. We have seen how the atomic nature of electricity was proved and that it is possible to measure the effect of a single unit of charge. We will now examine into the method of getting at the value of the charge. Millikan showed that the velocity with which a drop moves is proportional to the force acting on it and independent of the electric charge except as it affects the force. Accordingly, in which vi and v2 are the velocities of the drop under the influence of gravity and of the electric field respectively, F the field intensity, en the charge on the drop, m the mass of the drop and g the gravity constant. If the mass of the drop were known, it would be an easy matter to evaluate e, but the mass of a single small drop can be known only through Stokes's Law already referred to, which gives the velocity v1 of a drop of radius a and density o falling under the influence of gravity in a medium of viscosity as follows: Combining this with the first equation and eliminating m by means of the formula which contains only constants or easily measured quantities. On finding that drops of different sizes gave different values of e, Millikan questioned the validity of Stokes's Law and initiated a series of elaborate experiments at the Ryerson laboratory to find the correction which must be applied in the case of very small drops. At the same time the coefficient of viscosity of air, which appears in the formula in the 3/2 power, was determined with great accuracy and a new apparatus of great refinement was constructed. After about two years of work the final value of e was announced in 1916 as follows: e = 4.774.005 X10-10 absolute electrostatic units. To indicate the importance of this result, we quote from The Electron: "As soon as e is known it becomes possible to find with the same precision which has been attained in its determination the exact number of molecules in a given weight of any substance, the absolute weight of any atom or molecule, the average kinetic energy of agitation of an atom or molecule at any temperature, and a considerable number of other important molecular and radioactive constants. In addition, it has recently been found that practically all of the important radiation constants like the wave-lengths of X-rays, Planck's h, the Stefan-Boltzmann constant o, the Wien constant c2, etc., depend for their most reliable evaluation upon the value of e. In a word, e is increasingly coming to be regarded, not only as the most fundamental of physical or chemical constants, but also the one of most supreme importance for the solution of the numerical problems of modern physics." ARTICLES IN CURRENT PERIODICALS. American Botanist, for August; Joliet, Ill.; $1.25 per year, 35 cents a copy: "Plant Life on the Peaks," Blanche H. Soth; "How Brazil Nuts Grow," H. E. Zimmerman; "Uses of Cacti," Paul G. Russell. American Journal of Botany, for November; Brooklyn Botanic Garden; $5.00 per year, 60 cents a copy: "Effect of Soil Temperature on the Growth of Bean Plants and upon Their Susceptibility to a Root Parasite," Donald Reddick; "The Development of Cortinarius Pholideus," W. H. Sawyer, Jr.; "Leaf-structure as Related to Environment," Herbert C. Hanson. American Mathematical Monthly, for November; 5548 Kenwood Ave., Chicago; $3.00 per year: "The Significance of Mathematics," E. R. Hedrick; "The Linear Function and the Line," Joseph Nyberg; "The Graph of F(x) for Complex Numbers," A. F. Frumveller; "An Intrinsic Equation Solution of a Problem of Euler," P. R. Rider. Geographical Review, for November; Broadway at 156th Street, New York City; $5.00 per year, 50 cents a copy: "Aeronautical Maps and Aerial Transportation," Henry Woodhouse; "Saving the Crops from Injury by Frost," Alexander McAdie; "The Virgin Islands of the United States," Theodore de Booy; "The Lau Islands of Fiji," W. G. Foye; "The Distribution of British Cities, and the Empire," Mark Jefferson. Journal of Educational Psychology, for October; Baltimore, Md.; $2.50 per year, 30 cents a copy: "The Power of the Eye to Sustain Clear Seeing under Different Conditions of Lighting," C. E. Ferree and Gertrude Rand; "The Effect of External Incentives on Improvement," J. C. Chapman and R. B. Feder; "A Detailed Study of Whipple's Range of Information Test," J. C. Bell; "Aphasic Performance in the Terman Vocabulary Test," F. L. Wells. Journal of Geography, for December; Madison, Wis.; $1.00 per year, 15 cents a copy: "Suggestions for Teaching Elementary Geography,' R. H. Whitbeck; "The Food Surplus of South America Available in Time of War," George B. Roorbach; "The Use of Geographic Materials," Robert M. Brown; "Wheeling, West Virginia (Map)," Helen M. Garden; "The Condition of Geography in the High School and Its Opportunity," Carl O. Sauer; "Newfoundland," E. M. Jones. Photo-Era, for October; Boston, Mass.; $2.00 per year, 20 cents a copy: "System in the Studio," Pirie MacDonald; "Tone-Rendering and Quality in Gaslight-Papers," T. D. Tennant; "A Use for Old Bromide Paper,' S. Watmough Webster; "Picturing Children Afield," Charles J. Adams; "Focusing in Portraiture"; "Six Years, Twelve Tears and a PinholeCamera," Edwin B. Whiting; "Holding a Vest-Pocket Camera," Charles R. Denton; "Restoring Daguerreotypes," C. E. Bold. Physical Review, for November; Ithaca, N. Y.; $6.00 per year, 60 cents a copy: "Oscillating Systems Damped by Resistance Proportional to the Square of the Velocity," J. Parker Van Zandt; "An Experimental Investigation of the Total Emission of X-Rays from Certain Metals," C. S. Brainin; "The Pressure Increase in the Corona," Earle H. Warner; "The Ionizing Potentials of Gases," A. L. Hughes and A. A. Dixon; "A Determination of the Ratio of the Specific Heats of Hydrogen at 18°C. and 190°C.,” Margaret Calderwood Shields; "Theoretical Considerations Concerning Ionization and 'Single-Lined Spectra,' H. J. Van Der Bijl; "The Parallel Jet High Vacuum Pump," William W. To Study the Work of Worms on Soils A metal cage of ample size, fitted with glass front and glass partition. Dry and wet soil, or humus and sand may be placed 30-245 side by side. This Cage clearly illustrates the work of worms under controlled conditions. First Year Science Leaflet, No. 2, with full instructions, supplied with the cage, or mailed on receipt of six cents. Apparatus for All Sciences. Supplies fully guaranteed. Cambridge Botanical Supply Company LABORATORY EQUIPMENT-ALL SCIENCES 1 to 9 Lexington Street Waverley, Mass. THE AMERICAN MATHEMATICAL MONTHLY OFFICIAL JOURNAL OF The Mathematical Association of America Is the Only Journal of Collegiate Grade in the Mathematical This means that its mathematical contributions can be read and understood by those who have not specialized in mathematics beyond the Calculus. The Historical Papers, which are numerous and of high grade, are based upon original research." The Questions and Discussions, which are timely and interesting, cover a wide variety of topics. The Book Reviews embrace the entire field of collegiate and secondary mathematics. The Curriculum Content in the collegiate field is carefully considered. Good papers in this line have appeared and are now in type awaiting their turn. The Notes and News cover a wide range of interest and information, both in this country and in foreign countries. The Problems and Solutions hold the attention and activity of a large number of persons who are lovers of mathematics for its own sake. There are other journals suited to the Secondary field, and there are still others of technical scientific character in the University field; but the monthly is the only journal of Collegiate grade in America suited to the needs of the non-specialist in mathematics. Send for circulars showing the articles published in the last two volumes. 55 East Lorain St. OBERLIN, OHIO Please mention School Science and Mathematics when answering Advertisements. Crawford; "A Determination of the Efficiency of Production of X-Rays," Paul T. Weeks; "A Study of Apparent Specific Volume in Solution,' Leroy D. Weld and John C. Steinberg; "The Absorption of Mercury Vapor by Tin-Cadmium Alloy," L. A. Welo. Popular Astronomy, for December; Northfield, Minn., $3.50 per year: "Zenith Meteors," William H. Pickering; "Are the Spiral Nebulae Milky Ways?" M. G. Renaudot; "How to Determine the Correct Time Without Apparatus and Without Knowing the Meridian," Ernesto Nelson; "The 100-inch Telescope at Mount Wilson," Jennie B. Lasby. School Review, for November; University of Chicago Press; $1.50 per year, 20 cents a copy: "A Statistical Study of the Scholastic Records of 404 Junior and Non-Junior High-School Students," Paul Clifford Stetson; "Supervised Study and the Science Laboratory," Elliot R. Downing; "The Junior High School," L. McCartney; "The Supervision of ExtraCurricular Activities," Elmer Harrison Wilds. School World, for November; Macmillan Company, London, Eng.; 78. 6d. per year: "The Secondary-School Examinations Council"; "Books on the Method, Philosophy, and History of Science," R. A. Gregory; "Modern Humanistic Studies," C. H. C. Osborne; "Schools and Public Libraries," John Swain; "Standardising and Competitive Examinations." FORTY-FIVE MILLION BARRELS OF SALT. The domestic consumption of salt in 1916 was 45,720,860 barrels of 280 pounds each, an increase of more than 7,000,000 barrels over the consumption of 1915. According to statistics compiled under the direction of R. W. Stone, of the United States Geological Survey, Department of the Interior, the domestic production of salt in 1916 was 45,449,329 barrels, the imports were 871,992 barrels, and the exports 600,461 barrels. This was an increase of 19 per cent in the quantity of salt produed. The total value of the salt was $13,645,947. Michigan, as usual, was the largest producer, and New York was a close second. The production, in barrels, by the leading states was as follows: Michigan, 14,918,278; New York, 14,087,750; Ohio, 6,706,193; Kansas, 4,564,793; California, 1,124,236. Perhaps the most marded feature in the salt industry in 1916 was the great increase in quantity of brine sold as such or used by chemical works, the increase being 37 per cent and the total production over 18,000,000 barrels. The production of rock salt increased over 17 per cent and amounted to 9,973,950 barrels, valued at $2,665,270. On the other hand, the production of evaporated salt increased only 5 per cent, to 17,575,629 barrels, but the value was $10,149,412, an increase of nearly 15 per cent. ATTENTION! The date of the expiration of each subscciption will be printed with the address on the wrapper. This date will be your receipt, and no other receipt will be sent unless specially requested. This does not apply to members os associations whose subscriptions are sent in by the treasurer of the association. Back Numbers Wanted. For copies in good condition of Vol. 2, No. 3, May, 1902, we will allow 30c on subscriptioe or 25c cash. For Vol. 1, No. 2, April, 1901, we will allow 50c. Caldwell and Eikenberry Elements of General Science A logically arranged and well-balanced series of topics selected from the pupil's everyday environment and drawing from any of the sciences as they are needed. $1.00 McPherson and Henderson A First Course in Chemistry A book prepared especially to provide a brief course for beginning students in high schools who expect to pursue the subject no further. It is adequate, however, to meet college entrance requirements. $1.25. An Elementary Study of Chemistry Second Revised Edition An elementary treatment for beginners in colleges or normal schools. $1.25 SCHOOL TEXTBOOKS for the SECOND SEMESTER Are You Selecting the Best Books for Use in Your Schools next Semester? If not, Hasten, for Time Flies. An examination of our Textbooks for Secondary Schools will convince you that they rank among the best. They include: is simple. FARM MANAGEMENT—Andrew Boss. This is a suitable text on agriculture. ALGEBRAS-Williams and Kempthorne. Plenty of easy problems. Manner of approach ARITHMETIC OF BUSINESS-O. S. Smith (just out). A happy title. It treats the growing complexities of business. GEOMÉTRIES, PLANE AND SOLID-Williams and Williams. These books are made for teaching specific values. HIGH SCHOOL PHYSICS-Reed and Henderson. Pupils readily understand Reed and |