The Birmingham age-herald., 1924-08-03

removes tremendous retardlng force from the bullet which is believed to be the explanation of this puzzling proposition. Perhaps this mystery may be completely cleared up by a seri,J of spark photographs.
 The extent to which spark photo. graphy can be carried is only q matter of conjecture. Mir. Quayle says that the apparatus is so complete that it's en- tire operation is automatic, so that the operator need only set up the plate load the gun, and turn on the motor switch, the gun going off itself when everything is ready.
 Not only has this method speeded up photography, but it has also sharp ened human vision. It is possible with the illumination given by the spa rk to see the proiectile in it's flight, due to the persistence of visual images When seen this way the bullet seems suspended in midair. Mir. Quayle's lat est work with the spark camera has been t0 investigate the formation of gases at the muzzles of guns when the projectile has just left the barrel. and he expects to publish some valuable data on this subject in the near future
 Should Not Mystify
 Actual. photography of sound, brought to new extremes of accuracy and efficiency by the spark camera" should not mystify those who remember the principles of sound from high school and college physics textbooks-for sound, of course, is not an utterly intangible conception but a very def mite type of disturbance in the at mosFaere or some other medium which move8 at definite rates of speed, ac- cordaag to what it is passing through.
 Just as a rock thrown into still water starts waves moving away from it in all directions, so the explosion of a gun, the striking of base drum, or of a piano string starts sound waves moving away from it in all directions projectile has ust left the barrel and These waves constitute sound. But while the waves from the ,rock move at different speeds, according to their length, the sound waves always travel ct approximately the same speed. Sound waves in air. travel JOSS feet per second at freezing temperatures, and two feet more per second for each de- gree Centigrade of temperature, above freezing For this reason it is possible to see the lightning before the thunder is heard.
 Sound waves travel at different speeds in different mediums. As has been said, sound travels through air at about HOO feet per second. In sea water the speed of sound is 4,S0O feet or nearly mile per second, and in an atmosphere of hydrogen gas it is over 1000 feet per second. When a object such as a rifle bullet. moves through the air at a speed greater than that of sound it piles up sound waves which radiate from it's path like water waves from the bow of boat. These waves are known as bow waves, and it IS these waves which are heard when a high power rifle bullet passes over ones head.
 In one of the photographs above is shown a picture of bullet and these bow waves. They consist of a conical film of air compressed by the passage of the bullet. The lines in this par ticular photograph depart from the bullet at an angle of about 30 degrees, signifying that the bullet is travelling at oyer twice the speed of sound. As the bullet slows up the angle becomes more obtuse, until it nearly reaches 90 degrees, denOting tha tthe bullet is travelling only slightly faster than sound. When the bullet travels slower than sound, of course, the lines dis appear altogether.
 Through Soap Bubble
 A strange phenomenon involved by this last mentioned fact is observed when the bullet passes through a soap bubble filled with hydrogen. As the speed of sound in hydrogen gas is over 2,700 feet per second, the speed of the bullet, the bullet in passing through the bubble travels at a speed relatively slower than sound. Therefore, no bow waves are created by the projectile while it is passing through the bubble. A picture of this condition shows the bow waves as they would appear under ordinary circumstances except for break on each side where they had been cut off by the atmosphere of hydrogen in the bubble.
 Most interesting of all it is q photo graph showing q Spitzer bullet after having pierced the sides of soap bubble. It will be seen in the photo graph that the bubble has not been dis turbed except where it's walls have been shattered by the entrance and exit of the bullet The sound waves in this case have assailed the sides of the bubble and left them unharmed, al- though they are powerful enough to persons ears. This picture was taken about one fifty-thOusandth of a second after the bullet had passed through the bubble. before the bubble had had time to burst. Scattered over the picture are to be seen little spots, due to drops of water which were spattered over the negative when, the bubble burst after having been pierced by the projectile..
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