1840] WRITINGS OF JOSEPH HENRY. 187 



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 suggested, (78,) 

 may be prolonged beyond that of the natural subsidence 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 instant, would be one of constant 

 quantity during nearly the whole time represented 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 paragraph, then the quantity of the second- 

 ary current will begin to decline before the termination of 

 the induction, or as soon as the increments of the primary 

 begin to diminish ; and hence the whole time of the sub- 

 sidence of the secondary will be prolonged, or the length of 

 b C, Fig. 20, will be increased, the descent of B C be more 

 gradual, and the intensity of the ending induction of the 

 secondary current be diminished, (see last part of paragraph 

 78.) 



90. Besides the considerations we have mentioned, (88,) 

 there are others of a more obvious character, which would 

 also appear to affect the form of particular parts of the curve. 

 And first we might perhaps make a slight correction in the 

 drawing of Figs. 17, 18, &c., at the point A, in consideration 

 of the fact that the very first contact of the end of the con- 

 ductor with the surface of the mercury is formed by a point 

 of the metal, and hence the increment of development 

 should be a little less rapid at the first moment than after 

 the contact has become larger; or in other words, the curve 

 should perhaps start a little less abruptly from the axis at 

 the point A. Also, Dr. Page has stated* that he finds the 

 shock increased b}' spreading a stratum of oil over the sur- 

 face of the mercury; in this case it is probable that the ter- 



*Silliman's American Journal of Scifince. 



