ThermoeJectrical Properties of Iron under Stress, 45 



The Eulerian equations of motion are 



K v -f)=°- 



Giving 



V-* +irf[l-(^=|) 2 ](^+/)= const. 



Since Y= const. — ^(Ax 2 + ~By 2 + Cz 2 ), the surface 



+ ^ + ^=1 



can be free if 

 giving 



2 4a 2 & 2 _ Aa 2 -Cc 2 _ B5 2 -Co 2 

 W (a 2 + 6 2 ) 2- a 2 ~ c 2 ; * ' ^ ^ 



which was the condition found before. 



As this case of motion is very interesting physically, and 

 has only been discussed in memoirs devoted largely to other 

 objects, I have thought it worth while to give these proofs. 



VII. The Effect produced on the Th ermoelectrical Pro- 

 perties of Iron when under Stress or Strain by raising the 

 Temperature to Bright-red. By Herbert Tomlinson,!?.^!.* 



THE author has already had the pleasure of communicating 

 to the Physical Society t the results of some experi- 

 ments relating to a certain curious behaviour of iron wire 

 when under stress or strain at a temperature of bright red. 

 It was found that if the metal was under a slight stress either 

 of torsion or of flexure, there was apparently a sudden 

 increase of elasticity when, on heating, the critical tempera- 

 ture had been reached ; that is to say, if the wire was under 

 a slight twisting stress it suddenly untwisted, and if under a 



* Communicated by the Physical Society ; read November 26, 1S87. 

 t Pbil. Mag. vol. xsiv. Sept. 1887, p. 256. 



