Magnetisation in the Length of Metal Rods. 131 



0*75 mm. Brass wires were soldered to the ends in the usual 

 manner. 



The permanent magnetisation induced by the strongest current 

 appeared not to cause a permanent retraction of more than one scale 

 division. The temporary retractions produced by increasing mag- 

 netising forces are given in Table II and in fig. 6. The retractions 



Fig. 6. 



are of much greater extent than the elongations of iron under similar 

 circumstances, and though the curve affords evidence of an approach 

 to a limit, it is nevertheless clear that a considerable further retrac- 

 tion would have occurred if the current had been increased beyond 

 the power of rny battery. 



I also made a deflection experiment with the nickel, thinking it 

 might possibly be the case that it had no turning point., i.e., that the 

 ratio of the temporary moments to the magnetising forces decreased 

 ab initio. It appeared, however, that the turning point was unusually 

 well marked, occurring with a current of 0*042 ampere. The details 

 are given in Table III and fig. 6. The experiment was repeated two 

 or three times with the same result, the nickel having been in each 

 case previously magnetised with a strong current. The distance 

 between the centre of the galvanometer needle and the nickel was 

 15 cm. 



The behaviour of a stretched nickel wire has, I believe, never 

 hitherto been investigated. I therefore made the experiment with a 

 nickel wire 0*5 mm. in diameter, loaded with a weight equivalent to 

 about 2 lbs. The result of magnetisation was a very considerable 



k 2 



