the flyer in his work at the front, but made possible the socalled ballistic wind corrections upon which the effectiveness of both the artillery and the sound-ranging services largely depended. When it is remembered that the biggest element in the effectiveness of a modern army is its artillery and that the effectiveness of the artillery is dependent entirely upon these wind corrections it will be seen how incalculably valuable the work of the trained physicists and mathematicians proved to be to the practical problems of the great war. The sixth and last of the new applications of physics to the purposes of the war has to do with the principle of signaling by visible light rays, by infra-red rays, by ultra-violet rays and by super-sound rays. In all of these fields there were developments of great interest and of much importance for the future, though none of them contributed largely to the victory of the Allies. In bombardments all the wire and wireless methods of communication often failed and light signals of some sort were the only reliance. Special signaling lamps were developed by the Science and Research Division of the Signal Corps and ordered in considerable numbers. A notable system of secret signaling with infra-red rays was developed by Theodore Case of Auburn, N. Y., and successfully used in keeping convoys together at night when lights could not be used. The possibility of having secret ultra-violet methods of guiding aviators at night back to their landing fields was demonstrated by R. W. Wood. As already indicated super-sound signaling under water was successfully accomplished by Dr. Langevin and applied experimentally in submarine detection. Outside the lines of the foregoing classification there were some developments in Physics which deserve mention. Thus a leak proof gasolene tank for airplanes, developed by Dr. Gordon S. Fulcher in collaboration with the Miller Rubber Company of Akron, Ohio, which could be shot through by scores of bullets without leaking a drop of gasolene or catching fire even when the bullets were incendiary, had at the close of the war been ordered placed on all American combat planes. It promised to do away with the chief terror of the American flyer, namely, coming down in flames. An airplane compass and a speedmeter developed by Major Mendenhall and Lieut. Williamson, in coöperation with the General Electric Company were used on all American planes. Dr. Duff, Captain Webster, Captain Sieg and Captain Brown increased notably the accuracy in bombing, a matter of the greatest importance since doubling the accuracy in dropping bombs is more than equivalent to doubling the production of bombing planes. Under the stimulus of the war Dr. Coolidge developed a new and improved x-ray tube for use in field hospitals. Dr. E. F. Nichols developed a new type of mine, which was used in mining operations in the North Sea. Prof. A. A. Michelson developed a new and improved range finder, which was accepted by the Navy Department. Prof. Raymond Dodge developed a new piece of physical apparatus for the selection and training of gunners. This instrument was adopted and used both by the American and foreign navies. Optical glass was produced in large quantities for the first time in the United States under the guidance of a committee of the Physical Science Division of the Research Council, consisting of Drs. A. L. Day, S. W. Stratton and R. A. Millikan. This is but an incomplete sketch of what look now like the most important developments in Physics which were stimulated by the war. Scores of other problems were undertaken the results of which may in the end be as useful both for the purposes of war and for those of peace as any of those herein set forth. IV SOME SCIENTIFIC ASPECTS OF THE METEOROLOGICAL WORK OF THE UNITED STATES ARMY 1 T ROBERT A. MILLIKAN HERE is no more interesting illustration of the application of new scientific methods to warfare than is furnished by the developments in meteorology during the great war. Prior to 1914 a meteorological section was not considered a necessary part of the military service. No corrections had ever been made by the artillery of any army for any save surface winds. Firing by the map was almost unknown. No Sound-ranging Service, no Air Service and no Antiaircraft artillery had ever existed to demand aërological data. At the time of the signing of the armistice on the western front the Air Service and all the artillery were being furnished every two hours with the temperature, density, wind-speed and direction, taken at the surface and at various altitudes, from 100 to 500 meters apart, up to 5,000 meters. Further, tables were prepared from which each battery could obtain the correction suited to its trajectory for the so-called ballistic wind. This is the average wind for the trajectory, weighted for the density of the air at the elevations traversed. Even machine guns when used for barrage work made use of these ballisticwind tables. In addition, daily forecasts were furnished to the armies in accordance with the following outline: 1 Reprinted by permission, with the omission of certain illustrations, from the Proceedings American Philosophical Society, vol. 58, 1919. A. Character of weather for each arm of the service. B. Winds: Surface, at 2,000 m., at 5,000 m. C. Cloudiness including fog and haze. D. Height of cloud. E. Visibility. F. Rain and snow. G. Temperature. H. Warning of weather conditions favorable for use of gas by enemy. K. Probable accuracy or odds in favor of forecast. Most of the aërological data were obtained from theodolite observations on pilot balloons. The extent to which our knowledge of the upper air has been, and is being, extended by this pilot balloon work may be seen from the fact that before the war there existed but one station in the United States where pilot balloon explorations were regularly carried on. Within a year of the inception of the meteorological service in the United States Army, thirty-seven complete stations for the obtaining of both surface and upper air data in aid of aviation and the artillery had been established in the United States and equipped with special aircraft theodolites and pilot balloons, neither of which had ever been produced before in this country. Further, twenty such stations had been established by our forces abroad. For the manning of this service, about five hundred specially selected men had been trained in this country, and three hundred and fourteen of them sent abroad, while about two hundred were held for work in the United States. The scientific interest in this service centers about four distinct problems: I. The extension of our knowledge of the law of motion of pilot balloons. 2. The procurement of data and the development of methods for the preparation of artillery range table. |