186 Colonel H. Watkin on Chronographs. [May 1, 



ments now enable us to obtain records of the passage of a shot up 

 the bore of a gun to an accuracy closely approaching the millionth 

 of a second. 



There is one thing, however, we have failed so far to get, and that 

 is the velocity of a shot immediately outside the muzzle of the gun. 

 There is no doubt that for a short space of time the shot is accelerated, 

 but how far the acceleration extends is not known. 



To try and obtain this we had a strong steel bar fastened to the 

 muzzle and projecting some 10 feet from it. In this were screwed the 

 same kind of plugs as those I have already described, only that the 

 steel wire was of much stouter gauge. The experiment was, however, 

 a failure. The two plugs that were cut just before the tail end of 

 the shot left the bore were properly recorded, but the moment the 

 shot cleared the bore, the blast rushing past the shot caused irregular 

 results. 



Three years ago I proposed another method, which is just about 

 to be tried, viz. that the drum of the chronograph be covered with a 

 sensitive photographic film, the whole apparatus to be enclosed in a 

 box and fitted with a lens. In the gun is a shot filled with magnesium 

 composition ; this is ignited electrically just before the gun is fired. 

 As the drum with the film will be in rapid revolution, I hope to get a 

 streak of light impressed on the film by the magnesium shot as it 

 leaves the gun. This will form a curve which, from the known 

 speed of the drum, will give the exact speed of the shot at every moment 

 from leaving the muzzle to a distance of 20 or 30 feet in front of the 

 gun. From a small experiment I made in my workshop this seems 

 hopeful,* as I obtained a streak of light across a photograpic plate, 

 from a magnesium torch fired from a pistol. 



A useful adaptation of the revolving drum is to ascertain the 

 velocity of recoil of rifles and guns, &c. Across the drum is a slide, 

 which runs along a groove and presses lightly on its smoked surface. 

 As the slide is pulled by the recoil, the drum at the same time 

 revolving at a known speed, we get a curve which gives the velocity 

 of the recoil at every moment. 



I tried in this way to get the curve of the first start of a shot in 

 the 12 pr., a steel wire being fastened to the shot, and led through the 

 breech block to the chronograph placed on the carriage immediately 

 behind. The result was a failure, as the wire broke almost immediately. 

 This possibly might have been got over by thicker wire had the 

 experiment been carried on. 



* Since the lecture some of the experiments have taken place, and show that 

 most distinct records can be obtained in this way. The twist of the shot is also 

 shown, as there were two exits in the shell. 



[H. W.] 



