the Galvanic Current through Iron. 3 



exactly comparable. The mean values of the times required 

 for equal heatings are : — for 



Copper .... 478*9 



German silver . . 460*4 



Platinum . . . . 451*7 



Iron 448*0 



(4) When we close a circuit consisting of a battery and a 

 rectilineal iron wire, we observe an extra current in the oppo- 

 site direction to that of the principal current*. At the open- 

 ing of the circuit an extra current arises with the same direc- 

 tion as the principal current. These currents were discovered 

 by Villari, and were named shock-currents. G. Wiedemann f 

 at first based an explanation of them on the assumption of a 

 transversal or circular magnetization of the iron wire ; Her- 

 wigj and Streintz § have since engaged in a more detailed 

 investigation of them. 



(5) Longitudinal magnetizing of iron rods or wires has an in- 

 fluence upon their resistance. I mention this point last because 

 the results hitherto obtained respecting it have proved most 

 anomalous and in part contradictory to one another. Edlund 

 and Mousson found no alteration, Thomson || and Beetz *f[ in- 

 crease of the resistance ; while even a diminution was inferred 

 from older observations, and has recently been confirmed. 

 Beetz's results have lately been corroborated by Chwolson** in 

 a brief communication. 



§ 3. In the experiments and considerations which I have 

 carried out upon the facts here brought together, I started 

 directly from the last two points, partly because here the ma- 

 terial in hand appeared to me least sufficient for the full un- 

 derstanding of the phenomena, partly because I considered 

 that I could not concur in the view (in which Beetz and 

 Herwig agree) that the cases treated by them (4 and 5) must 

 be kept perfectly distinct. Bather have I, with G. Wiede- 

 mannf t, received from their results the conviction that the 

 two phenomena may very well be connected with one another, 

 and hence are to he contemplated from a common point of view. 



* The current made use of for the measurement, passing through the 

 iron, I shall constantly in the following designate as the principal current. 



t Galvanismus, 2nd ed. ii. 2, § 743 (1873). 



\ Pogg. Ann. vol. cliii. p. 115 (1874). 



§ Wien. Ber. vol. lxxvi. (1877). 



|| Phil. Trans. 185C, p. 737. 



«I Pogg. Ann. vol. cxxviii. p. 202 (18C6). 

 ** Carl's Rep. vol. siii. p. 232 (1877). 

 tt Galvanismus, 2nd ed. ii. 1, p. 593. 



B2 



