ON ELECTRO-DYNAMIC INDUCTIONi 33 



therefore be rendered comparatively feeble by being obliged to pass through a 

 small portion of heated air; very little effect is therefore produced on the helix 

 by this induction^ (19.) The fact that this current is capable of giving intense 

 shocksj when the ends of a long wire, which is transmitting a primary current^ 

 are grasped at the time of breaking the circuit, is readily explained, since, in 

 this case, the body forms, with the conductor, a closed circuit, which permits 

 the comparatively free circulation of the induced current. 



88. It will be seen that I have given a peculiar form to the beginning and 

 ending of the curves, Figs. 17, 18, &c. These are intended to represent the 

 variations which may be supposed to take place in the rate of increase and de- 

 crease of the quantity of the current, even in the case where the contact is made 

 and broken with mercury. We may suppose, from the existence of analogous 

 phenomena in magnetism, heat, &c., that the development of the current would 

 be more rapid at first than when it approximates what may be called the state 

 of current saturation, or when the current has reached more nearly the limit of 

 capacity of conduction of the metal. Also, the decline of the current may be 

 supposed to be more rapid at the first moment, than after it has lost somewhat 

 of its intensity, or sunk more nearly to its normal state. These variations are 

 indicated by the rapid rise of the curve. Fig. 17, from A to g, and the more 

 gradual increase of the ordinates from h to B; and by the rapid diminution of 

 the ordinates between C and /, and the gradual decrease of those towards the 

 end of the curve. 



89. These more minute considerations, relative to the form of the curve, will 

 enable us to conceive, how the time of the ending of the secondary current, as 

 we have stlggested, (78,) may be prolonged beyond that of the natural subsi- 

 dence of the disturbance of the electricity of the conductor on which this current 

 depends. If the development of the primary current is produced by equal 

 increments in equal times, as would be the case in plunging the battery (59) 

 into the acid with a uniform velocity; then the part A B of the curve Fig. 17 

 would be a straight line, and the resulting secondary current, after the first in- 

 stant, would be one of constant quantity during nearly the whole time repre- 

 sented by Ac; but if the rate of the development of the primary current be 

 supposed to vary in accordance with the views we have given in the last para- 



VIII. — I 



