the Galvanic Current through Iron* 



149 



No. 



s v 



u v 



&,. 



u & . 



Siuks to 



1 



4-3 



23 



52 



4-0 



2-6 



2 



49 



2-9 



6-0 



3-9 



2-9 



3 



52 



30 



61 



3-9 



? 



4 



5-5 



3-4 



6-4 



4-1 



34 



5 



56 



3-5 



66 



4*1 



? 



Means... 



5-1 



3-0 



6-1 



4-0 



30 



Of the slow increase of all the numbers from experiment to 

 experiment I shall speak presently. 



Here belong also some facts already alluded to: — thus 

 the phenomenon that, even in the cases in which the mag- 

 netizing diminishes the resistance, the first experiment gives 

 the opposite result ; for the evolution of heat occasioned by 

 friction in the performance of work continues to operate. 

 Further, the opening has often an influence in the opposite 

 direction ; that is, the resistance is lessened by magnetizing 

 where otherwise it would be augmented, or is more strongly 

 depressed than it would otherwise be. This phenomenon ap- 

 pears especially striking on the reversal of the current (com- 

 pare § 4, experiment-series 10 and 11). 



Some of the various phenomena just described may, I 

 think, with more justice be designated as specific magnetic 

 aftereffect*; but I here confine myself to a brief statement f. 

 First, the intensity of the extra currents increases at the frequent 

 passage of the current, or at frequent magnetization. This 

 phenomenon has already been observed by Herwig ; and he 

 has explained it by an increasing mobility of the particles. 

 The second of the above Tables shows it very clearly. At 

 the same time it follows that the afteraction in consequence 

 of the performance of work, which is the subject of that 

 Table, does not simultaneously increase ; for the numbers 

 u 2 are nearly constant, and the difference u 2 — u 1 sinks from 

 1*7, through 1*0, 0'9, 0*7, to 0*6. In connexion with this 

 is the fact that the resistance of iron generally increases not in- 

 considerably on the current being repeatedly conducted through it. 

 This phenomenon must not be confounded with that observed 

 by Yon Quintus Icilius — namely, that the resistance of all 

 metals is increased after a single long-continued passage of a* 

 current through them. The phenomenon is much more pro- 



* I see, from a memoir by Fromme, just published (Wied. Ann. iv. 

 p. 76), that he also uses the same expression -for analogous phenomena. 



t Conf. Herwig, Streintz, I. c. : and further, Herwig, Pogg. Ann. clvi. 

 p. 430 (1875). 



Phil Mag. S. 5. Vol. 8. No. 47. Aug. 1879. M 



