174 WRITINGS OP JOSEPH HENRY [1840 



found at the beginning only of the battery current, while, if 

 the galvanometer were consulted, we would percoive the 

 effects of a current as powerful at the ending as at the begin- 

 ning. 



67. The results mentioned in the last paragraph cannot 

 be obtained by plunging a battery into the acid ; the forma- 

 tion of the current in this way is not sufficiently rapid to 

 produce a shock. The example was given to illustrate the 

 manner in which the same effect is supposed to be produced, 

 in the case of the more sudden formation of a current, by 

 plunging one end of a conductor into a cup of mercury per- 

 manently attached to a battery already 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 

 general 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 experi- 

 mental nature which would lead us to the same conclusion, 

 (18,) (90,) and also to the further inference that the decline of 

 the current is not instantaneous. According to this view 

 therefore the inductive action 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 

 diminution 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, 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 break- 

 ing 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 of the metal to conduction; 

 and this we might suppose would be more rapidly overcome 



