130 Mr. James Mackenzie Davidson [April 25, 



by dividing a wire by a bullet fired from a pistol. He^sbowed that 

 the sudden break gave the full-length spark in the coil without 

 using a condenser. I at once tried the effect of this discharge 

 through an X-ray tube and found that a very brilliant illumination 

 of the tube took place sufficient to take a photograph (show photo- 

 graph on the screen). It then occurred to me that if I interposed 

 the revolver nozzle with the wire in front of it, between the tube 

 and the photographic plate, that possibly a flash from the X-ray 

 tube would be quick enough to cast a shadow of the bullet in its 

 flight on the photographic plate immediately after the division of 

 the wire had taken place. This I accomplished (show slide on the 

 screen). The shadow of the bullet is blurred showing that the X- 

 rays flash had lasted too long, and this in marked contrast to the 

 beautifully sharp photographs taken of bullets by Professor Boyd 

 by means of the discharge Leyden jar. I repeated this experiment 

 with a revolver with a muzzle velocity of 800 feet per second, and 

 found in two independent negatives that the track of the bullet was 

 approximately the same length and had begun at the same distance 

 from the broken wire. With a Mauser pistol, the muzzle velocity 

 being 1400 feet a second, I failed to get an image of the bullet 

 within 10 inches of the stretched copper strip, but got several blurred 

 images of this copper strip, which on this occasion I used instead 

 of wire; the vibrations produced in the broken strip giving rise 

 to many shadows according to its varying positions. The results of 

 the experiments go to show that with the revolver which had an 

 initial velocity of 800 feet a second wherever oscillations may have 

 been produced in the coil, the duration of the X-ray flash was about 

 ^uVo ^^ ^ second. I will now show you the flash in the tube 

 interposing the fluorescent screen by dividing this wire by the pistol, 

 which I now show you. I advise you to close your ears so that the 

 noise may not interfere with your observing the flash. 



We now pass on to the action that X-rays have upon the photo- 

 graphic film. Rontgen rays while producing changes in photographic 

 plates in many respects similar to light yet differ in some important 

 respects. For example, I have here six films. In the dark-room 

 they were placed in a bag superimposed like a pack of cards. I put 

 my fingers upon the films and gave a short exposure to the X-rays. 

 The films were numbered, the top one numbered one and so on, and 

 the last one numbered six. On developing these films all in the 

 same way, hardly any difference could be detected, the first and last 

 were almost equally good, so that the X-rays do only partial work 

 in producing a photograph, although the first film produced a firm 

 strong negative, yet sufficient rays pass through and do equally good 

 work on the films below. 



There is one advantage in this that in cases where one is doubtful 

 of the exposure, two or more films can be placed together and if the 

 exposure be correct two negatives are obtained, and if the exposure 

 has been too short by accurately superimposing the films a picture 



