238 
DR. J. YOUNG AND PROFESSOR G. FORBES ON THE 
and also 
whence 
t b : 
2mN 
B 
V=4mN B .D B 
2 m(n + n' )B b 
r+1 
7. If, however, —~ be not quite exactly equal to g , let 
r +1 
our equation becomes 
and 
2 r(g+p+8)=^t±£(n+n') 
B 
_ n + n' g + p 
B 2 r g + p + 8 
n + n' / 8 
S 3 
2r 
and 
cj+p (g + pf 
y 2m(n + n')D B ^ ^ 8 S 3 
g+p (g+p ) 3 
By employing the first term alone, in this last factor, we obtain an approximate value 
of N b which enables us to calculate the value of p on the supposition that k—k—\ 
(which is always very closely arranged so in practice). Thus we find the value of the 
small correction involved in the second term. The third term can always be neglected 
in our experiments. 
8. To find the approximate value of p under these circumstances, we have now the 
two first equations in § 6, reduced to 
i i 9 n fi ■ n 
l+ N =P\ 1 - r 
N 
By 
and 
Adding these we have 
and 
1- 
g(n'—n ) 
/5= 2N B -( n '-n) 
9+P 
_ 
B 
2N b — (n'~ n) 
also 
