130 Mr. S. Bidwell. On the Changes produced by 



and temporary magnetisations, while those in the third and fourth 

 were produced by the temporary magnetisation only. The results 

 are given in Table V and in the subjoined curves (fig. 5). Both series 



Fig. 5. 



are interesting as affording an illustration of the law which has been 

 fully investigated by Sir William Thomson,* that the magnetisation 

 of a wire is at first increased and afterwards diminished by stretch- 

 ing ; but the results of the second series only (in which the ordinates 

 represent the temporary moments) are comparable with those of the 

 former experiments. + 



Referring to the curve of temporary magnetisation, it will be seen 

 that the magnetising current at the turning point is reduced by 

 stretching with a weight of 7 lbs. from 0*051 to 0*030 : presumably, 

 therefore, the magnetising current for the critical point is at the 

 same time reduced from about 0*102 to 0"060, and a current between 

 these limits would be accompanied by elongation when the wire was 

 un stretched, and by retraction when it was stretched. 



For a few experiments made with nickel, a strip was used of the 

 following dimensions: — Length 100 mm., breadth 9 mm., thickness 



* "Phil. Trans.," 1876 and 1579. 



f It should be noticed that the ordinates are on a different scale in the two 

 diagrams, as may be seen by comparing the figures at the side. The distance between 

 the wire and the centre of the galvanometer magnet was 13 cm. in all the experi- 

 ments. 



