13° Cincinnati Society oj Natural History. 



Since tlie fall of the chronometer rod follows the law of fall of 

 ^leavy bodies, we have the formula T'l^j/? H . which istheequa- 



g 

 tion of this macliine. Now T' represents the time which the 

 ■chronometer rod occupies in falling (the distance H), supposing 

 ■every part of the machine to act instantaneously, but there is a 

 ■delay in the action of the first magnet, which would shorten the 

 "value of the time, we therefore designate it by — M. 



There is a delay in the action of the second nmgnet, which 

 upholds the short or "register rod,'' designate this by -|- M' ; a 

 delay due to the time required by the short rod to fall on the trigger, 

 call this -j- t'; next we have a delay caused by the time recpiired 

 for the disengagement of the trigger, equal to -f- t" ; and lastly a 

 a delay required for the knife to reach the chronometer rod, call 

 this correction -j- t'", consequently we must correct the value of T' 

 by subtracting the sum of these quantities. Designating the true 

 time by T, we now find tliat T^T— (M' f t'4-L"+t'"— M) or 

 calling the sum of the corrections t we liave 'r^=:T' — t. 



The value of (t) the sum of the corrections can be obtained by 

 ■nirans of the device called the "Di-junctor ;" it serVes to break the 

 -electric currents from both targets at the same instant, and the 

 ■Jiick made by the knife on the chronometer rod will mark a point 

 called the "di-juiictor reading." Commencing with this point as the 

 ■oiii;in, or O ptjint, we get the corrected value T' - t, that is the true 

 value T. 



A graduated rule, or scale, is used for measuring the height of 

 the nick above the zero point. If you have the scale calculated for 

 adistince of fiftv yards, the velocity of the projectile can be at 

 once determined. Should it be necessary to place the targets 

 iii'irer, the velocity can be found by multiplying the number read 

 -off the scale by the actual distance between the targets divided 

 by fifty. The height of the nick on the chronometer rod above 

 the "origin" is given by the formula H=y2g T'^. 



In the chronoscopes which have pendulums in place of the 

 roJs, the time due to the arc of oscillation can by the theory of the 

 pendulum be readily ascertained. 



Benton's chronoscope recommends itself on account of its great 

 simplicity, as it dispenses with the necessity of voltaic batteries. 

 ]t operates by the means of threads which are stretched from the 

 targets to the pendulums, the threads in being ruptured by the pro- 



