MR. V. W. DYSOX ON THE POTENTIAL OF AN ANCHOR RING. 
63 
and drawn the equipotential surfaces. The method consisted in drawing circles of 
known radii, with centres, C and ; and finding the value of V at their points of 
intersection. 
In the most unfavourable case, where a = c, the value of the potential is not more 
than three per cent, in error at any point, the introduction of the terms in 
reduces the error to less than one and a half per cent. When a < c, the approximation 
is considerably nearer. 
Fig. I. 
Equipotential surfaces of ring formed bj 
the revolution of the point C about Or. 
If Mass = id I 
and 0 C = c J 
Then — is taken = I 
c 
