344 RECENT PEOGRESS IN PHYSICS. 



current both in the copper plate and in the secondary spiral, hut the 

 current in the secondary spiral cannot induce a current in the main 

 spiral, because the latter is not closed by metal, the two coatings of 

 the jars being separated by glass. The only possible influence of the 

 current in the secondary spiral upon that ii^the main spiral is some 

 retardation of the discharge. , 



Now, if the closure of the secondary spiral is more perfect than that t 

 of the main spiral, the current of the former will pass more rapidly 

 than that of the latter, and on that account no reaction of the second- 

 ary spiral can take place upon the main spiral ; hence, with a more 3| 

 perfect closure of the secondary spiral, the temperature in the conduct- - 

 ing circuit is found very little less than when no secondary spiral is * 

 present. 



With an imperfect metallic closure of tbe secondary spiral the 

 secondary current has a longer duration, and then the discharge cur- - 

 rent in the main wire finds, during its whole course, the secondary ■ 

 wire traversed by a current passing in the same direction, and we ; 

 must assume that this is the cause of the retardation of the main cur- • 

 rent, which is indicated by the diminished temperature ; by imperfect ^ 

 closure of the secondary spiral the temperature in the main current 

 was reduced in the proportion of 0,43 to 0.17. 



By inserting a tube of water into the secondary spiral the tempera- 

 ture again increases almost as much as though no secondary spiral 

 had been present, which is well explained by the fact that, with very 

 imperfect closure of the spiral, no sensible secondary current is gen- 

 erated. 



The circumstance that, with quite perfect as well as with very im- 

 perfect closure of the secondary spiral, the influence on the main wire 

 is less than for a moderately good closure, leads us to expect that, 

 when the secondary spiral is closed by constantly increasing lengths 

 of thin wire, at first the temperature of the main circuit will decrease, 

 that, with a given length of the introduced wire, the influence of the 

 secondary spiral will become a maximum, and then decrease again, and 

 that, therelbre, the elevation of temperature of the conducting circuit 

 of the main spiral will again increase when the wire by which the 

 secondary spiral is closed is lengthened. 



This was verified by experiments which Riess made. — (Pog. Ann., 

 LI, 177.) 



Representing by 100 the temperature observed in the thermometre 

 introduced in the conducting circuit of the main spiral, the secondary 

 spiral being closed by a short thick copper wire, the results given 

 by the insertion of a German silver wire 0.1517 line diameter and of 

 different lengths, are as follows: 



