220 Dr. F. Auerbach on the Passage of 



was found to bo 



w " +1 ~^ n =3=0-048. 



W n 



So colossal an alteration of resistance (almost 5 per cent.) 

 could not have escaped the observers, and is moreover in itself 

 improbable ; it even overpasses the limits of the alterations of 

 resistance by magnetizings as above given (§ 6). 



A third series of experiments, finally, showed that when the 



current passed through continuously the resistance diminished 



enormously; there was, namely : — 



a j. £ j. After Ao-ain, K ~ e . , 



At first. n • nP o o> o, 5 minutes. 



1 mm. after 3, ' 



w 



= 16-54 16-23 16-01 15'92 15-83 15-82 (constant). 



The current was then opened for a short time, and again 

 closed ; a reiterated diminution of w was the result ; at 

 w= 15*70 constancy appeared to have come in again; and so 

 it went on. All these phenomena may at once be characterized 

 as consequences of the disturbed molecular relations of the 

 wire. 



Even with new wires there is one difficulty not unimportant. 

 By every alteration of the electromotive force the thermal 

 equilibrium of the wire is disturbed, as the radiation for some 

 time does not keep pace with the increased heating. In one 

 branch of the bridge, however, which consists exclusively of 

 German silver, the heating has very little, but in the other, in 

 which is the iron wire, an important influence. I have en- 

 deavoured to approximately determine this influence from the 

 numerical data supplied by Weber, Favre, and Bosscha. In 

 Bosscha's units the electromotive force of a Daniell is in round 

 numbers 10 11 , therefore in Volta's units of current and 

 Siemens' s resistance-units 10. Now, in operating I constantly 

 added only one element (never more) at a time. We shall 

 therefore obtain an upper limit for the heating if we calculate 

 the heating by 2D ; that effected by ID is not sufficient, be- 

 cause the heating increases as the square of the electromotive 

 force at constant resistance. We have thus the electromotive 

 force E = 20; and the mean of the total resistance of the two 

 sides of the tetragon through which the current flowed was 

 exactly the same — namely, 10 in the comparison branch (?6' 2 , 

 conf. § 3), and 10 on the average in the iron wire. The cur- 

 rent-intensity is therefore = 1. At the same time, according 

 to Favre, 1"6 unit of heat is generated, therefore 0*8 in the 

 iron wire. The weight of the latter amounted to at least 

 10 x 01 x 10000 = 10000 milligrams, or 10 grams. These 10 

 grams of iron are about as much heated as 1 gram of water 



