Vol. Ill, N"o. 7-J Muynetu- Induction in Spheroids. 447 



iN.S.] 



1 1 fsiiiS^ cosS^l 



Also -; = 77 -5 — r + , , 



or 2^ 





to) 



p 



and c?.^ = /,2^;53cos8^. ^/a^T. sin 5 i<^ (i^ 



2nj{r-^-\) sinOde S(2/. +1) P.(^) P.(^') QJ/) . 



~d^' 



remembering that <f> terms disappear on integration between limita 

 and 27r. 



Finally, since 



dr r2-l' 



o> 



i 



1) 



N 



Or, tbe potential (V) due to a current t\ circulating in the wire is 



27rz-[^Q,(r') (/. 



1) + 



2 -r-rr F«f/i') Qn{r') (r«- I) (l-/x«) -r-.-^ 



7. To calculate tlie poteutial due to several turns of wire, we 

 liave to find the mean value of V in the first place. 



i.e., calculate 



Vdcda 



dcda . 



r— — - drdfi 

 rf(r/Lt) 



I 



8(ca) 



where c= distance of any windin^r of wire from the origin 



flf = radius of the Avinding 



