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Invisible light in warfare
838
CURRENT TOPICS.
[J.F.I.
(Bull. Anz. Issf. Mi&g and MetalWater Power of France. September, IgIg.)-In the Alpine region lurgical Engineers, drained by the Rhone and its tributaries 6,000,ooo horsepower can be developed at average water flow. Elsewhere in France 3,ooo,oo0 horsepower additional may be obtained from streams. These numbers should be divided by two to get the output for lowwater flow. At the close of 1915, 738,000 horsepower was obtainable from installations in the Alps. This amount has ,been much increased since that time. G. F. S. Depreciation in Small Dry Cells with Age. A. J. HELFRECHT. (Americarn Electrochemical Society, 1919.)-The author endeavors to show how closely the method of judging cell deterioration, called “flash test,” approaches actual measurements of capacity through discharging the cells,. Comparative curves for the different sizes of cells tested are given. From the data gained by this investigation a table has been compiled indicating reasonable depreciation of the four important sizes of small cells. The Effect of Amalgamation Upon the Single Potential of Aluminum. LOUIS KAHLENBERG and JOHN A. MONTGOMERY. (American Electrochemical Society, IgIg.)-Measuring the single potential of aluminum in a one-third molar solution of aluminum chloride at room temperature, by means of the calomel electrode, the writers obtained much higher values with amalgamated than with unamalgamated aluminum, due to the removal of the coat of resistant oxide by the mercury. They showed also that the measurements were actually the single potentials of the aluminum and not those of an aluminum amalgam. Invisible Light in Warfare. R. W. WOOD. (Proceedi’sgs of the PhysicaN Society of London, vol. xxxi, p. 232, IgIg.)-When a source of light is put at the principal focus of a converging lens the emergent beam consists of parallel rays and consequently does not change in cross-section as it proceeds. Often the narrowness of such a beam prevents its being observed. Greater accuracy was obtained by using a filter which permitted only the extreme red r’ays to issue. These would be invisible to an observer unless he protected his eyes from daylight by a similar screen. Through such a screen only the red light could penetrate and the eyes of the observer would be in a sensitive state owing to the exclusion of ordinary light. By such an arrangement secret signals can be transmitted. A variation of method was the use of a screen transmitting only ultra-violet light, which was received on a fluoresThe range of signalling in both cases was about cent screen. six miles. The following arrangement proved of great value in maintaining communication between ships of the same convoy at night. In this case the light was sent out not as a parallel beam, but as a
I-kc.. 1910.1
C‘UIIRENT TOPICS.
beam diverging in all directions. A Cooper-Hewitt mercury arc was the light source. It was surrounded by a glass chimney This caused parts through which only ultra-violet light emerged. of the eye and natural teeth to fluoresce, while false teeth were black. The receiving apparatus is a barium-platino-cyanide screen placed in the principal focus of a converging lens. The range was about four miles. G. F. S. Location of Aeroplanes by Wireless Telegraphy. J. ROBINSON. (Nature, September II, IgIg.)-Dead reckoning methods are of little use for such a purpose owing to the pilot’s ignorance of the velocity of the air with respect to the earth. A loop of wire exposed to electrical waves has an E.M.F. developed in it which varies in strength according to the relation of the plane of the loop to the direction in which the waves are travelling. By changing this spatial relation and by noting the effect upon the current induced in the loop it is possible to find the location of the aeroplane. The Germans did this by sending waves out from the aircraft and by receiving them on loops at various places on the ground. Observers at a central station worked out the position of the source of the waves and sent the information to the aeroplane. The Royal Air Force solved the problem by having a loop on the aeroplane receive waves from several stations. The bearing of each station was worked out by the aerial observer and from this he worked out his position. As wireless signals are noted by the ear, difficulty was found in applying this method owing to the noises of the wind and of the engine. This obstacle was overcome by increasing the strength of the signals. Electrical disturbances emanating from the magneto were avoided by shielding the machine. Two loops, main and auxiliary, with planes at right angles to each other were mounted on the aeroplane. When the loops have this relative position one has its maximum current when the other has its minimum. Suppose the main loop is turned until its current is a maximum and that then the auxiliary loop is joined to the main one. A little later the auxiliary loop is joined in the reversed direction. As this loop had no current, reversing it makes no difference. If, however, the main loop was not accurately in the position for maximum current, the auxiliary loop would have a current in it and reversing it would make a difference. The procedure is to rotate the main loop until its position for maximum current is approximately found. Then the auxiliary coil, always at right angles to the other, is introduced into the circuit first in one direction and then in the other, and the two loops are rotated about their common axis until no change in the intensity of the signals is caused by reversing the auxiliary loop. Then the position of the plane of the main loop to the direction of propagation of the waves is known.
CURRENT TOPICS.
[J.F.I.
(Bull. Anz. Issf. Mi&g and MetalWater Power of France. September, IgIg.)-In the Alpine region lurgical Engineers, drained by the Rhone and its tributaries 6,000,ooo horsepower can be developed at average water flow. Elsewhere in France 3,ooo,oo0 horsepower additional may be obtained from streams. These numbers should be divided by two to get the output for lowwater flow. At the close of 1915, 738,000 horsepower was obtainable from installations in the Alps. This amount has ,been much increased since that time. G. F. S. Depreciation in Small Dry Cells with Age. A. J. HELFRECHT. (Americarn Electrochemical Society, 1919.)-The author endeavors to show how closely the method of judging cell deterioration, called “flash test,” approaches actual measurements of capacity through discharging the cells,. Comparative curves for the different sizes of cells tested are given. From the data gained by this investigation a table has been compiled indicating reasonable depreciation of the four important sizes of small cells. The Effect of Amalgamation Upon the Single Potential of Aluminum. LOUIS KAHLENBERG and JOHN A. MONTGOMERY. (American Electrochemical Society, IgIg.)-Measuring the single potential of aluminum in a one-third molar solution of aluminum chloride at room temperature, by means of the calomel electrode, the writers obtained much higher values with amalgamated than with unamalgamated aluminum, due to the removal of the coat of resistant oxide by the mercury. They showed also that the measurements were actually the single potentials of the aluminum and not those of an aluminum amalgam. Invisible Light in Warfare. R. W. WOOD. (Proceedi’sgs of the PhysicaN Society of London, vol. xxxi, p. 232, IgIg.)-When a source of light is put at the principal focus of a converging lens the emergent beam consists of parallel rays and consequently does not change in cross-section as it proceeds. Often the narrowness of such a beam prevents its being observed. Greater accuracy was obtained by using a filter which permitted only the extreme red r’ays to issue. These would be invisible to an observer unless he protected his eyes from daylight by a similar screen. Through such a screen only the red light could penetrate and the eyes of the observer would be in a sensitive state owing to the exclusion of ordinary light. By such an arrangement secret signals can be transmitted. A variation of method was the use of a screen transmitting only ultra-violet light, which was received on a fluoresThe range of signalling in both cases was about cent screen. six miles. The following arrangement proved of great value in maintaining communication between ships of the same convoy at night. In this case the light was sent out not as a parallel beam, but as a
I-kc.. 1910.1
C‘UIIRENT TOPICS.
beam diverging in all directions. A Cooper-Hewitt mercury arc was the light source. It was surrounded by a glass chimney This caused parts through which only ultra-violet light emerged. of the eye and natural teeth to fluoresce, while false teeth were black. The receiving apparatus is a barium-platino-cyanide screen placed in the principal focus of a converging lens. The range was about four miles. G. F. S. Location of Aeroplanes by Wireless Telegraphy. J. ROBINSON. (Nature, September II, IgIg.)-Dead reckoning methods are of little use for such a purpose owing to the pilot’s ignorance of the velocity of the air with respect to the earth. A loop of wire exposed to electrical waves has an E.M.F. developed in it which varies in strength according to the relation of the plane of the loop to the direction in which the waves are travelling. By changing this spatial relation and by noting the effect upon the current induced in the loop it is possible to find the location of the aeroplane. The Germans did this by sending waves out from the aircraft and by receiving them on loops at various places on the ground. Observers at a central station worked out the position of the source of the waves and sent the information to the aeroplane. The Royal Air Force solved the problem by having a loop on the aeroplane receive waves from several stations. The bearing of each station was worked out by the aerial observer and from this he worked out his position. As wireless signals are noted by the ear, difficulty was found in applying this method owing to the noises of the wind and of the engine. This obstacle was overcome by increasing the strength of the signals. Electrical disturbances emanating from the magneto were avoided by shielding the machine. Two loops, main and auxiliary, with planes at right angles to each other were mounted on the aeroplane. When the loops have this relative position one has its maximum current when the other has its minimum. Suppose the main loop is turned until its current is a maximum and that then the auxiliary loop is joined to the main one. A little later the auxiliary loop is joined in the reversed direction. As this loop had no current, reversing it makes no difference. If, however, the main loop was not accurately in the position for maximum current, the auxiliary loop would have a current in it and reversing it would make a difference. The procedure is to rotate the main loop until its position for maximum current is approximately found. Then the auxiliary coil, always at right angles to the other, is introduced into the circuit first in one direction and then in the other, and the two loops are rotated about their common axis until no change in the intensity of the signals is caused by reversing the auxiliary loop. Then the position of the plane of the main loop to the direction of propagation of the waves is known.