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Air Bubbles for Nullifying Submarine Explosions TO the Editor of the Scientific American: I have recently made some experiments in a small way to test some of the suggestions that have been made in your valuable paper in the course of recent discussion on torpedo defence. These were as follows: A 45-caliber Colt blank cartridge was inserted in an iron block having a bore as long as the shell and mounted in the middle of a barrel filled with water so that it could be easily exploded. In this experiment No. 1, the effect of the explosion resembled the striking of a 10 pound sledge hammer on the floor; the barrel rocked slightly but no water was thrown out. In experiment No. 2, a thin rubber air bag was placed immediately under the cartridge, which had about one pint capacity. The arrangement was such that upon explosion the blast of the cartridge would enter directly into the submerged air bag. The result was a shock of less suddenness but of such volume as to sound like a heavier but slower striking sledge hammer. It almost upset the barrel and blew part of the water up out of it. In experiment No. 3, a jet of air was set free immediately under the cartridge, causing a kind of foam or at least.a myriad of air bubbles and walls of water between them, into which cellular mass the charge was fired. The result was almost complete nullification of the shock. Compared to the first experiment, it was like hitting the floor with a padded one-pound hammer. Commenting on the experiments, No. 2 illustrated the tremendous destructive power of an explosive charge as in a torpedo or mine when it is backed by a solid unyielding body of water on one side, and a yielding medium permitting full expansion of the gases, as the air-backed hull of the ship, on the other side. It appeared in this instance, that not only did the gases have a chance to expand fully, helping to bring about complete combustion, but time enough was allowed to overcome the inertia of the resisting media on a more voluminous scale. In experiment No. 3, there appears to be conclusive evidence of the feasibility of Hudson Maxim's idea of resisting explosions by an intermediate arrangement of air and fluid cells. The intervening cell walls of water in the air jet experiment were shattered and atomized, forcing the energy of the explosion to do a large amount of mechanical work. The air bubbles of course did act as a cushion to a certain extent but the hot gases appeared to be instantly cooled by the very large cooling area of the atomized particles of water. In my estimation, the explosive force of a mine or torpedo in direct contact, is so ponderous that if it be allowed a solid sea backing with the interior of the ship as the only path of least resistance, it will crush in a cellular protection of water and air even though very deep. I believe, however, that if the density of the surrounding water could be reduced at least for the critical moment so that the modified Maxim idea may be made to work outside of the ship as well as inside, a surprisingly small amount of damage would be done by an ordinary mine or torpedo explosion. To produce the cellular effect outside of the ship, no draught resisting outrigging would be needed. A series of air nozzles could be arranged near the bilge of the hull, running along its entire length, but equipped with a system of valves for selective discharge. Air could be stored under pressure in tanks. Since it is possible to see the approach of a torpedo, a volume of air could be released in the vicinity it is about to strike. It is in the foam caused by the air discharge that the major part of the explosion would occur. It would then become a yielding medium to relieve to a large extent the penetrative force against the yielding hull of the ship. New York. Albert F. Shore. "To the Kaiser" To the Editor of the Scientific American: I want to thank you for the timely and vigorous editorial in the Scientific American issue of September 8th, 1917 entitled, To the Kaiser. I hope that it will be widely spread and read. I have seen it reproduced in one of the large daily papers of Philadelphia, and I think that a translation of it sent through the German Empire ought to open the eyes of a sadly misled people. A careful perusal of it might benefit a class of citizens who call themselves Americans, but whose words and acts, are to say the least, un-American and un-patriotic. Pittsburgh, Pa. Thos. D. GILLESPIE. Charles Forbes, M.D. THE world of invention has lost a worker of ability, and the Scientific American one of its subscribers of longest standing, through the death on October 2d of Dr. Charles Forbes, of Rochester, N. Y. Dr. Forbes was always able to find time, in a particularly active lifetime devoted mainly to medicine and medical instruction, to give free play to his interest in all things photographic and electric. During a connection of many years with Columbia University he designed more than forty pieces of laboratory apparatus in these three fields, many of which are still in general use. In addition to this andl to his work in dry-plate making, he is perhaps best known as the inventor of the gauze bandage, drain and sponge roller which have been adopted as standard by the American Red Cross Society, and as the designer of the first individual communion cups--a measure of cleanliness coming with peculiar appropriateness from a physician. Uncle Sam-Employment Agent for Engineers N normal times when an employer is in need of help he has only to post a notice in front of his establishment to secure the necessary hands. At times, however, he requires men of special qualifications who are not only skilled mechanically, but who also know the underlying principles of their occupation. Such men are never abundant, and frequently are quite scattered; hence much valuable time is lost to the employer and the available man in finding each other. With this in mind, the United States Department of Labor recently created, as a part of its employment service, a Division whose function it is to aid the employer in obtaining suitable help, and professional persons in securing suitable employment. While intended to embrace all professions, attention has thus far been confined to those of teaching and engineering. The methods of the Division are thorough, and no service is rendered the applicant until the Division has learned, from persons familiar with him, that he is qualified as to training, experience, and personal qualities for the position he seeks. When an applicant is recommended for a reported vacancy, the employer is given an opportunity to examine the data gathered in the course of this investigation, thus effectually preparing for the personal interview, for which facilities are provided in the offices of the Division. Employers and professional engineers everywhere are invited to avail themselves of the services of this Division which are entirely free. Employers in reporting positions are asked to state the nature of the position, its duties, requirements, etc., the probable salary, and probable duration of employment. Applicants for registration should indicate in the first letter the nature of the position desired so that the proper blank may be furnished. All communications should be addressed: Teachers and Professional Service Division, U. S. Employment Service, 845 South Wabash Avenue, Chicago, Ill. Panorama of Ashokan reservoir, the artificial lake from which New York City gets its mountain water
