34 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



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 second- 

 ary will be prolonged, or the length of b C, Fig. 20, will be increased, the descent 

 of 5 C be more gradual, and the intensity of the ending induction of the second- 

 ary 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 mer- 

 cury is formed by a point of the metal, and hence the increment of develop- 

 ment 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 spreading a stratum of oil over the surface of the mer- 

 cury ; 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 conductor is drawn up into a non- 

 conducting medium. 



91. The time of the subsidence of the current, when the circuit is broken by 

 means of a surface of mercury, is very small, and probably does not exceed the 

 ten thousandth part of a second, but even this is an appreciable duration, since 

 I find that the spark at the ending presents the appearance of a band of light 

 of considerable length, when viewed in a mirror revolving at the *ate of six 

 hundred times in a second; and I think the variations in the time of ending 

 of the current under different conditions. may be detected by means of this in- 

 strument. 



92. Before concluding this communication, I should state that I have made 

 a number of attempts to verify the suggestion given in my last paper, (III. 127,) 

 that an inverse induction is produced by a galvanic current by a change in the 

 distance of the conductor, but without success. These attempts were made 



* Silliman's Journal. 



