502 Prof. J, Henry's Contributions 



tor, however rapidly or slowly we may plunge the battery 

 into the acid, and however irregular may be the rate at which 

 it is drawn out, still if the whole effect be produced within the 

 time of one swing of the needle, the galvanometer is deflected 

 to an equal degree. 



66. Again, the intensity of one part of the inductive action, 

 for example that represented by Kg, may be supposed to be 

 so great as to produce a secondary current capable of pene- 

 trating the body, and of thus producing a shock* while the 

 other parts of the action, represented by g B and C D, are 

 so feeble as to affect the galvanometer only. We would then 

 have a result the same as one of those given in the last sec- 

 tion (42.), and which was supposed to be produced by two 

 kinds of induction ; for if the shock were referred to as the 

 test of the existence of an induced current, one would be 

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

 the galvanometer were consulted, we vv^ould perceive the ef- 

 fects 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 formation 

 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 the conductor into a cup of mercury permanently at- 

 tached 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 jje?- saltum. its maximum state 

 of quantity ; on the contrary, from the general law of con- 

 tinuity, we would infer that it passes through all the interme- 

 diate states of quantity, from that of no current, if the ex- 

 pression 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 further inference that the decline of the current is not in- 

 stantaneous. According to this view, therefore, the inductive 

 actions at the beginning and the ending of a primary current, 

 of which the formation and interruption is 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 al- 

 tered by a change in the different parts of the apparatus ; 



* The shock depends more on the intensity than on the quantity. See 

 paragraph 13. 



