to Electricity and Magnetism. SIS 



the disturbance of the electricity of the conductor on which 

 this current depends. If the development of the primary cur- 

 rent 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 A c ; 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- 

 graph, then the quantity of the secondary 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 subsidence of the secondary will be pro- 

 longed, or the length of b C, fig. 20, will be increased, the 

 descent of B C be more gradual, and the intensity of the end- 

 ing 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 conductor 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 by spread- 

 ing a stratum of oil over the surface of the mercury; in this 

 case it is probable that the termination of the current is more 

 sudden, on account of the prevention of the combustion of the 

 metal by means of the oil, and the fact that the end of the con- 

 ductor is drawn up into a non-conducting medium. 



91. The time of the subsidence of the current, when the cir- 

 cuit is broken by means of a surface of mercury, is very small, 

 and jn'obably does not exceed the ten thousanchh part of a se- 

 cond ; but even this is an appreciable duration, since 1 find that 

 the spark at the ending presents the appearance of a band of 

 light of considerable length, when viewed in a mirror revol- 

 ving at the rate of six hundred times in a second ; and I think 

 the variations in the lime of ending of the current under dif- 

 ferent conditions may be detected by means of this instrument. 



92. Before concluding this communication, I should state 



* Silliman's Journal. 

 Phil. Ma<r. S. 3. Vol. 18. No. 119. June 1841. 2 L 



