to Electricity and Magnetism. 503 



and, first, let us take the example of a single battery and a 

 short conductor, making only one or two turns around the 

 helix; with this arrangement a feeble shock, as we have seen 

 (11.), will be felt at the making, and also at the breaking of 

 the circuit. In this case it would seem that almost the only 

 impediment to the most rapid development of the current 

 would be the resistance to conduction of the metal : and this 

 we might suppose would be more rapidly overcome by in- 

 creasing the tension of the electricity ; and, accordingly, we 

 find, that if the number of the elements of the battery be in- 

 creased, 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 effect more minutely, we must call 

 to mind the fact before referred to (17.), that when the poles 

 of a compound battery are not connected, the apparatus ac- 

 quires an accumulation of electricity, which is discharged at 

 the first moment of contact, and which in this case would 

 more rapidly develope the full current, 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.), appears nearly the same as with a battery of a single ele- 

 ment, because the accumulation just mentioned, in the com- 

 pound battery, is discharged almost instantly, and, according 

 to the theory (71.) of the galvanic current, leaves the con- 

 stant current in the conductor nearly in the same state of 

 quantity as that which would be produced by a battery 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 considerations*, that when 

 the circuit is bi-oken by a cup of mercury^ the rate of the diminu- 

 tion of the current, "within certain limits, remains the savie, 

 hoxoever the intensity of the electricity or the length of the con- 

 ductor may be varied. 



Fig. 18. 

 B ^ C 



r D 



70. The several conditions of the foregoing examples are 

 exhibited by the parts of the curves, figs. 18 and 19. The 



* See the theory of Ohm. — Taylor's Scientific Memoirs, vol. i. p. 312, 

 511, and vol. ii. p. 401. 



