STRAIN ON THE PHYSICAL PROPERTIES OF MATTER. ^ 



simply on account of the heat generated by the magnetising solenoid, he proceeded as 

 follows : 



Efl" 'in,.',d XVIII. 



The magnetising solenoid described in the first portion of this memoir was placed 

 horizontally, and an iron wire of rather more than twice the length of the solenoid 

 was stretched along the axis of the latter and fixed at both ends. Water, as in 

 the earlier experiments, was kept constantly flowing through the annular space of 

 the air-chamber, so as to prevent the heat generated in the solenoid from affecting 

 the wire. The wire, when rubbed along its length with a resined glove, gave a clear 

 note, which was taken on a monochord. The magnetising solenoid was now excited 

 by ten GROVE'S cells, and the wire, having been loosened and stretched by the same 

 load as before,* was again secured at the ends and rubbed. The note yielded 

 was precisely the same as before, and, though the current 'was allowed to flow 

 through the solenoid for some time, not the slightest change could be detected. 

 Several trials were made of the same kind, and all concurred in yielding the same 

 results. Of course, the value to be attached to an experiment of this kind depends 

 mainly upon the ability of the observer to distinguish small differences of pitch. 

 Now the author's assistantt has so frequently proved his skill in this respect^ 

 that it can be fairly said that if longitudinal magnetisation does influence longitudinal 

 elasticity it does so to an extent which cannot be appreciated, even by a well-trained 

 ear, when tested in the above manner. It might, perhaps, be possible to detect some 

 effect of magnetisation on the temporary elongation produced by large loads when 

 the method of static extension is employed, but not with the arrangement used by 

 WERTHEIM. M. WERTUEIM seems to have taken no precautions to avoid the heating 

 effects of the magnetising solenoid, and the very fact that he was only able to detect 

 any change after the solenoid had been excited for sonic time points suspiciously to 

 heating as being the origin of what he observed. It is true that according to 

 WERTHEIM the longitudinal elasticity of iron is increased by a small rise of tempera- 

 ture, but in this the author has ventured to differ from him. 



The Influence of an Electric Current on Longitudinal Elasticity. 



According to WEHTHEIM|| the longitudinal elasticity of wires is diminished by the 

 passage of an electric current, independently of the alteration which would result 



* The full arrangement for effecting this will be described in a future paper, 

 t Mr. FUHSE, Uic Curator of the Museum of King George III., King's College, Strand. 

 J The author has already given (' Phil. Trans.,' 1883 (vol. 174, Part I.), p. 53 and elsewhere) 

 specimens of this. 



' Phil. Trans.,' 1883 (vol. 174, Part I.), pp. 128-131. 

 || 'Annales de Chimie,' vol. 12, 1844. 



