CAPTURING PERFECT PICTURES OF PROJECTILES IN FLIGHT BY THE USE OF AN M BY W. N. TAFT R. GUSTAV DIETZ, of New York, and Capt. Francis H. Behr, an official photographer of the Coast Artillery Corps, have solved the problem presented by the highest of high-speed photography by which the Army hopes to answer questions of ordnance which would almost certainly have remained riddles but for their invention. Their camera differs from the ordinary machine in only two particulars its size and its shutter. It is about four feet in height and each of its parts is, of course, correspondingly larger than that of the ordinary kodak. It (there is only one at present) is equipped with the finest two-inch lens, and great care is taken that this valuable piece of glass remains unspecked and unharmed by the dangerous gases which surround it during some of the tests. But the chief value of the novel camera lies in the shutter, which is the invention of Mr. Dietz. This shutter is operated by an electric motor that makes several thousand revolutions a minute. As the speed of this motor is capable of accurate adjustment, the photographer can determine the exact length of the exposure up to of a second. This is the shortest fraction of time during which the light waves will make a definite impression on the highly sensitized plates and, as it is possible to obtain clear photographs of THE PROJECTILE ALMOST OUT OF THE MUZZLE projectiles in flight with this exposure, Once the style of camera was definitely decided upon, the next problem was how to release the shutter at the exact time the shell was in the position desired. This was manifestly impossible through mere human means because the eye cannot even perceive the shell in flight, much less give the order necessary for the pressing of a button so as to catch the projectile in mid-air. Captain Behr worked out the following method as the most practicable: A delicate screen, formed of electrically charged wires, is placed in the muzzle of the mortar or rifle which is to be used in connection with the test. Other wires are attached to this screen and the camera is trained on the place where it is calculated the shell will be when the shutter clicks. As the speed of the projectile is a known quantity, being dependent on the strength of the charge, this is a simple problem in mathematics. Upon the firing of the gun the shell breaks the screen and completes the circuit, thus flashing the eye of the camera Copyright by the Department of Enlisted Specialists, C. A. S. THE SMOKE RING COMPLETELY OBSCURING THE PROJECTILE open for the fraction of a second necessary to record the flight of the projectile. By regulating the current and the speed of the electric motor it has been found possible to catch shells just as they leave the mouth of the gun, suspended in mid-air, or as they strike the target. In the latter case the screen which regulates the shutter is placed in front of the target instead of inside the gun itself. Captain Behr was forced to spend many months and thousands of dollars before he finally perfected his device for photographing shells in flight. The first photographs showed the projectile to be about eight feet long. This was because the exposure was ooo of a second, and during that time the shell traveled far enough to appear on the negative as twice its actual length. When the exposure was reduced to do, however, the impression of the shell was found to be clear, distinct, and in exact proportion. Captain Behr made a number of his most important experiments with mortars, the mainstay of the Coast Artillery Service. Before finishing its plans for the fortification of the Panama Canal the authorities of the War Department desired to obtain more accurate knowledge of the working of this integral part of the coast defenses. The dean of the army photographers was therefore chosen to carry on the experiments, and he discovered many things formerly unknown, secrets which will be extremely useful in any future war in which the United States may participate. With this unique camera Captain Behr succeeded in getting views of mortar shells in all positions, up to the time when they ceased their upward flight and started to descend. By a close inspection of these views a number of faults in connection with the mortars have been dis Copyright by the Department of Enlisted Specialists, C. A.S. MUSHROOMING" covered and will be remedied in all the new models as they are manufactured. The formation of the deadly "smoke ring" which immediately follows the issuance of the projectile was also accurately depicted by the Behr camera. The phenomenon of the smoke ring is one of the most peculiar connected with the mortars. Almost before the shell appears the ring of gaseous smoke can be seen. obscuring the muzzle of the gun and rising rapidly upward. Gunners claim that this smoke ring is rendered as hard as steel by reason of its centrifugal velocity, and the story is told at Fortress Monroe of a luck Copyright by the Department of Enlisted Specialists, C. A. S. AS THE SMOKE RING IS USUALLY SEEN BY THE EYE less seagull which flew into a "ring" several hundred feet in the air and, stripped of its feathers, was cast down upon the mortar, killed by the friction of the gas. Recent developments in photography have opened up a field of experimentation to army and navy officials in the science of ordnance which has previously been in complete darkness. The problem next to be attacked is: "What does a twelveinch shell do when it strikes armor? How does the steel act during the instant of penetration and what happens to the shell just after it explodes?" The answers to these questions may solve the problem of why an armorpiercing projectile with the hardest possible "nose," or point, will not itself penetrate armor. It must be "capped" with steel of the softest nature. This fact has been known for years. Its explanation is as yet undiscovered. Army officials expect to see, through the eye of the new camera, many things which have previously defied explanation. Thirty feet away from the armor plate the camera will show with absolute precision what the modern high-power shell does when it plows its way through Harveyized steel. From negatives showing pieces of a shell |