140 Contributiotis to Electricity and Magnetism. 



in the acid, and in full operation. The current, in this case, rapid 

 as may be its development, cannot be supposed to assume per 

 saltum its maximum state of quantity ; on the contrary, from the 

 genera] law of continuity we would infer, that it passes through all 

 the intermediate states of quantity, from that of no current, if the 

 expression may be allowed, to one of full development ; there are, 

 however, considerations of an experimental nature which would 

 lead us to the same conclusion, (18,) (90,) and also to the farther 

 inference that the decline of the current is not instantaneous. 

 According to this view, therefore, the inductive actions at the 

 beginning and the ending of a primary current, of which the 

 formation and interruption are effected by means of the contact 

 with a cup of mercury, may also be represented by the several 

 parts of the curve. Fig. 17. 



68. We have now to consider how the rate of increase or dimi- 

 nution of the current, in the case in question, can be altered by 

 a change in the different parts of the apparatus ; and, first, let us 

 take the example of a single battery and a short conductor, mak- 

 ing only one or two turns around the helix ; with this arrange- 

 ment, 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 conduc- 

 tion of the metal ; and this we might suppose would be more 

 rapidly overcome by increasing the tension of the electricity; 

 and, accordingly, we find that if the number of elements of the 

 battery 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 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 ra- 

 pidly develope the full current, and hence produce the more in- 

 tense action on the helix at making the circuit. 



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

 ing the circuit with a compound battery and a short coil, (9,) ap- 

 pear nearly the same with a battery of a single element, because 

 the accumulation just mentioned, in the compound battery, is 

 discharged almost instantly, and, according to the theory (71) of 



