ELECTRIC-SPARK PHOTOGRAPHS. 179 



portion of the velocity of a bullet is given to it after it has left the bar- 

 rel, or, what comes to the same thing', to find the position in front of 

 the barrel at which the speed is a maximum. The cause of this is evi- 

 dent. When the bullet has left the muzzle the imprisoned powder 

 gases, under enormous i^ressure, rush out, making a draft past the 

 bullet of the most tremendous intensity tending obviously to drive it 

 forward. While this draught does most assuredly hurry the bullet on 

 its forward course, it does not tend to make it spin round any faster. 

 Now if the bullet were not hurried on at all after it left the muzzle it 

 would, travelling as in a screw of the same pitch all the way from the 

 breech of the litle uj) to the point at which it is photographed, have 

 turned round a certain number of times, which depend upon the dis- 

 tance traveled and the pitch of the screw. If however the longitudi- 

 nal motion is hurried and the rotational is left unaltered the pitch will 

 be lengthened outside the barrel and the rotation will have been less 

 for any position than it would have been if the bullet had not been 

 accelerated in this way. If therefoie we can find to what extent the bul- 

 let has turned actually at the place at which it has been photographed, 

 we can find the apparent rotational lag, and so working backwards 

 get a measure of the velocity acquired after leaving the muzzle. In 

 order to accomplish this I drilled a series of holes transversely through 

 the bullet, each one at an angle to the previous one, the whole series 

 being such that to whatever extent the bullet had twisted, one at least, 

 and perhaps two, Avould allow the light of the spark to shine through 

 it upon the photographic plate. Then from the photograi)h it is easy 

 to see through which hole the light shone, and knowing in what 

 position this was in the breech, it is easy to find what fraction of half 

 a turn over or above any whole number of half turns the bullet has 

 twisted. Strictly the measure should be made at different distances 

 to eliminate all uncertainty, but the only shot I have taken was sulfi- 

 cient to show that there was a rotational lag equivalent, according to 

 the measure made l)y Mr. Barton, to something under a two per cent 

 acceleration outsule the barrel. I do not attachany importance to this 

 figure; the experiment was made with a view to see if the method was 

 practicable and this it certainly is. I would recommend, where ac- 

 curacy is required, that having" found as above about how much the 

 bullet has turned, that a second bullet should be drilled with a series 

 of holes at about the corresponding position differing very slightly from 

 one another in angular position, so that several w^ould let the light 

 through and thus give a more accurate measure of the rotation. 



There is a point of interest to sportsmen which has given rise to a 

 controversy which the spark photograi)hs supply the means of settling. 

 The action of the choke bore has been disputed, some having held that 

 the shot are made to travel more compactly altogether, while others, 

 while they admit that the shot are less scattered laterally, as may be 

 proved by firing at a target, assert that they are spread out longitudi- 

 nally, so that if this is the case the improved target i)attern is no cri- 



