The Shot-Gun. 787 



of vibrations per second of the fork was very small, and the 

 means of several such measures did not vary from one another by 

 more than one-tenth of a vibration, or, expressed in time, the varia- 

 tion did not surpass the TsVsth of a second. This fact showed that 

 the chronoscope, so far as its records were concerned, was sufficiently 

 constant and accurate for measures on the velocity of projectiles. 



The effect of temperature on the vibratory period of the fork had 

 been determined in a previous research. It amounts to an increase 

 of .000045 °f tne periodic time of the fork's vibration for an increase 

 of 1 deg. Fahr. in the temperature of the fork. 



The guns used in the experiments had rebounding locks. The 

 primary current of an induction-coil passed through a break-piece 

 fixed under the rebounding hammer, so that at the instant the 

 cartridge was exploded the electric current was broken and then 

 immediately formed again. The current which passed through 

 this break-piece was led by a wire to an upright piece of tin plate 

 whose front surface leaned against a thick copper wire. Another 

 wire led from the tin plate (which stood in a shallow trough of mer- 

 cury) back to the battery. One terminal of the secondary coil of the 

 inductorium is connected with the axis of the metal cylinder, the 

 other terminal with the foot of the fork. 



This chronoscope is worked as follows : One person vibrates the 

 fork with a bow, and then brings the pointed foil down on the 

 smoked paper and rotates the cylinder. While the fork is marking 

 its sinuous trace he cries " fire," and the other person discharges 

 the gun at the tin plate. At the instant the cartridge explodes, a 

 minute spark issues from the tracing-point of the fork and cuts a 

 small hole through the blackened paper in the sinuous trace of the 

 fork ; and when the tin plate is knocked over by the shot, another 

 similar spark flies from the tracing-point. 



We know the distance between the breech of the gun and the 

 tin plate ; the number of flexures in the trace of the fork contained 

 between the two spark-holes gives the time the shot took to go over 

 the known distance, whence the velocity of the shot per second is 

 readily computed. 



The fork used in these experiments made about 256 vibrations, 

 or flexures, in the trace in one second ; so, if there should appear 32 

 flexures between the two spark -holes, the record would give ^ths, 

 or one-eighth of a second for the time ^ flight of the shot from the 



