Kiess on Electric Currents of the First and Higher Orders. 179 



current was again measured ; the strength of the latter was found 

 to be quite unchanged by this closing of the spirals. If, how- 

 ever, instead of being closed by a short copper wire, the ends of 

 one of the secondary spirals were united by increasing lengths of 

 fine platinum wire, the principal current was observed to decrease 

 to a certain limit, from which forward it increased. A secondary 

 current induced by a primary thus circumstanced may be ex- 

 pected to partake of the fluctuations of the latter, which conclu- 

 sion has been established experimentally by the author in his 

 present investigation. The primary circuit contained two induc- 

 tion-discs, and the secondary two others ; the ends of one of the 

 secondaries were united to the thermometer by short copper 

 wire ; the two ends of the other secondary were united, first 

 by a short copper wire, and afterwards by increasing lengths of 

 platinum wire of 0-028 of a line radius. The following table 

 gives the result of the experiments : — 



Closing of the second spiral. 

 Copper 16inches. Platinum 1-98 feet. 5*95 179 37-6 97-2 

 Secondary current in the first spiral. 



100 75 53 35 37 51 



Here we observe that the effect of the platinum wire in weak- 

 ening the principal current was a maximum when its length was 

 17-9 feet; and that the effect of a wire 5-95 feet in length was 

 very nearly equal to that of a wire 97-2 feet in length. 



The mediate action of one secondary current upon another is 

 established by the foregoing experiments; for the secondary 

 current in a spiral is shown to be modified by the action of an- 

 other distant secondary spiral upon the principal current. But 

 the direct action of one secondary upon another can also be 

 shown by permitting both to be induced by the same portion of 

 the primary circuit. The experiment is frequently so arranged, 

 that, besides the spiral whose secondary current is observed, 

 another spiral is introduced, either between the former and the 

 primary circuit, or at the opposite side of the latter. Instead of 

 spirals, metallic bodies have been sometimes introduced ; and it 

 has been found that the better conductor the body is, the greater 

 will lie the weakening of the secondary current; to this action 

 Henry has applied the term " screening." The precise action 

 winch takes place will perhaps be best understood from the dis- 

 cussion of the next table, which contains the results of a number 

 "I experiments conducted in the following manner: — Round a 

 wooden cylinder, 18 inches high and Gi inches diameter, three 

 topper wires were wound spirally. Bach wire was /jths of a 

 line in thickness, 53 feet long, and made 31 revolutions, possess- 

 ing a * pitch ' of 44 lines. The first spiral was introduced into 



N2 



