350 Dr Searle, Comparison of nearly equal electrical resistances. 
Expanding each of the denominators as far as the second term, we 
have . 
3 iAtptq—-Atpteyjat+ a +r +5— (Aq rs) as, 
=4{B+ris—(B+r+syP/bh,4+B+p+q—-(B+pt+q)/b}- 
Since p, q, 7, s are very small compared with A or B, we may 
neglect 2Ap/a,, 2pq/a,, p*/a, and similar terms. We then obtain — 
A-%(++2)-B-5 (G4; 
DONG a 2 ND oy a 
Here we may write AB for A? and for 5’, and then we find 
AB 7 ea 
ACES ata eee 
b 
which is identical with equation (7) of § 2. 
