TIIKItMAL CONDUCTIVITIES OF SOME ELFXTTUICAL INSULATORS. 445 



Or, since for this spiral 6 0, 



i5w* Tr.-in 



. HITS 



sin -j- 



r.- 



3 HIT* 







HIM 



Similarly tor tlie mean temperature 0, of the secoud spiral, for which p = 2c, 6 = v, 

 we have 



nw 



r2c 



rr 



" 



-IT/ 



Hence, for the difference f\-P of mean temperature of the spii-ala, we have 







ir=i tt 



ttir.s 

 IT 



K 



1 



or, 



K 



K ( nira \ 



' 



