1840] 



WRITINGS OF JOSEPH HENRY. 



175 



by increasing the tension of the electricity ; and accord- 

 ingly we find that if the number of elements of the bat- 

 tery be increased, the shock at making the circuit will also 

 be increased, while that at breaking the circuit will remain 

 nearly the same. To explain however this jeffect more 

 minutely, we must call to mind the fact before referred to, 

 (17,) that when the poles of a compound battery are not con- 

 nected, the apparatus acquires an accumulation of electricity, 

 which is discharged at the first moment of contact, and 

 which in this case would more rapidly develop the full cur- 

 rent, and hence produce the more intense action on the 

 helix at making the circuit. 



69. The shock, and also the deflection of the needle, at 

 breaking the circuit with a compound battery and a short 

 coil, (9,) appear nearly the same as with a battery of a single 

 element, because the accumulation just mentioned, in the 

 compound battery, is discharged almost instantly, and 

 according to the theor}'^ (71) of the galvanic current, leaves 

 the constant current in the conductor nearly in the same 

 state of quantity as that which would be produced by a bat- 

 tery of a single element; and hence the conditions of the 

 ending of the current are the same in both cases. Indeed, 

 in reference to the ending induction, it may be assumed as 

 a fact which is in accordance with all the experiments, (9, 

 13, 73, 74, 75, 76, &c.,) as well as with theoretical consider- 

 ations,* that when the circuit is broken by a cup of mercury, the 

 rate of the diminution of the current, within certain limits, re- 

 mains the same, however the intensity of the electricity or the 

 length of the conductor may be varied. 



A 



Fig. 18. 



D 



70. The several conditions of the foregoing examples are 

 exhibited by the parts of the curves. Figs. 18 and 19. The 



* Adopting here the theory of Ohm. 



