90 Mr. R. H. M. Bosanquet on the Magnetic 
(w x angle is used throughout to represent degrees, w being 
== i290). 
Let first approximation be denoted by one accent, second 
by two, and so on. 
Assume @6,/=60° Then 
fk 04 
ih 60° 4 
whence Sy 
oO! = aa 
ki - WY sin 6,/ 
p  60°—a6,! 
Second approximation. 
/ 
w6,! J 60° — nae zt 31, 
, p 
y7__ ®071 
vs w0,// 
whence 
pa b3 
In general this will be enough, but there is no difficulty in 
repeating the process as often as necessary. 
Dropping the accents, we have for calculating the right- 
hand side of (6), 
k 
B., Ho, 08s, f, D 
From the result find tan 6, whence 4, or rather 6. 
If the condition as to the maximum is satisfied by the 
assumed value of A, this w6 will coincide with wd. If they 
differ, as they generally will, the assumed value of A is wrong. 
If w(d—6,)! is positive, A has to be increased, and vice versa. 
Another hypothesis as to the value of A has then to be 
made, and the work repeated, (A”). 
The final value #(@—0,)” thus obtained, compared with 
w(@—6@,)’, offers a means of estimating the true value of A, 
for which the maximum of w given by the equations corre- 
sponds to the proper value of %. But the convergence of the 
process is not quick enough to enable differences to be used 
for the estimation, unless close approximation | as been already 
