by twisting Magnetized Iron and Nickel Wires. 127 



fields was observed. There we see that both in iron and 

 nickel the first increase of the field gives rise to rapid in- 

 crease- of the transient current. In nnstretched iron this 

 current attains its maximum strength at a field of about 

 5 C.G.S. units. It then gradually decreases as the field is 

 further increased. In nickel of nearly the same length and 

 thickness as the iron this current attains its maximum value very 

 slowly, so that it is difficult to ascertain precisely the strength 

 of the field at which this point is reached. Moreover, this 

 maximum, though not very distinct, occurs at a magnetizing 

 field far greater than that for iron. 



The application of longitudinal stress produces opposite 

 effects in the transient current in iron and nickel. The tran- 

 sient current due to sudden twist in iron always decreases Avhen 

 acted upon by pulling stress, whereas in nickel it diminishes 

 in low magnetizing field, but beyond a certain strength of the 

 magnetizing force the current in stretched wire attains 

 greater value than in the unstretched wire. Thus the maxi- 

 mum transient current in nickel increases with the amount of 

 longitudinal stress. 



The effect of pulling the wire changes, not only the amount 

 of the current, but also the strength of the field at which the 

 current attains its maximum value. The effect is similar in 

 both iron and nickel, although the amount of shifting of 

 maximum in the former is less than in the latter. 



That the transient current produced in twisting iron wire 

 reaches a maximum was first noticed by Professor Ewing ; 

 the method of procedure in his experiments being different from 

 the one here described. He measured the current produced 

 in a twisted wire by reversing the direction of the magnetizing 

 force. In the present experiment the current produced by 

 twisting the wire was observed. In one of Professor Swing's 

 experiments the transient current induced in an iron wire 

 34 centim. long and 1 millim. thick, and twisted through 60°, 

 passed a maximum when the strength of the field was 15 or 

 16 C.G.S. units. The wire used in the present experiments 

 cannot be much different from the one used by Professor 

 Ewing. The transient current attained its maximum value 

 for <£)= 5. Whether the discrepancy between these two re- 

 sults is due to the quality of iron wire or to the difference in 

 the method of procedure, is a question not easily to be 

 decided. 



A simple glance at the results hitherto obtained will show 

 the similarity between the phenomenon here investigated and 

 the Wiedemann effect. In the latter phenomenon the twisl 

 produced by magnetizing a circularly magnetized iron wire 



