APPENDIX I. 103 



will style chronoscopic circuit, the circuit of the 

 chronoscopic current. 



If, e. g., the velocity of a bullet, within the very 

 barrel of a gun, were to be measured, the chrono- 

 scopic circuit, in addition to the battery and the 

 galvanometer, should comprise a wire stretched out 

 just before the muzzle of the gun, the cock, which 

 in some way or other should be insulated from the 

 gun, and lastly the gun itself. Then at the moment 

 when the cock strikes the percussion-cap, the circuit 

 is made and remains so till the bullet tears the 

 wire; and so the current will only have lasted 

 during the time required for the explosion of the 

 percussion-cap, for that of the gunpowder in the 

 gun, and for the moving of the bullet along the 

 barrel. This time has been found to be from y^ to 

 Y^ of a second. By repeating the same experi- 

 ment with the wire or a net of wires at any greater 

 distance from the muzzle, and by taking the differ- 

 ence of the times required in both cases, the time 

 elapsed during the flight of the bullet through the 

 space comprised between the two positions of the 

 wire can be ascertained.* 



Application of this Method to our Problem by Pro- 

 fessor Helmholtz. The same method was, a few 

 years later (1850), successfully applied by Professor 

 Helmholtz to the solution of our problem. 



Suppose that the chronoscopic current, when its 



circuit is made, causes the muscle to contract by 



stimulating a motor nerve at a point A. It will be 



easy to arrange things so as to cause the muscle by 



* Comptes Bendus, &c., 1844, t. xix. f p. 1384. 



