674 
LORD RAYLEIGH OH THE VALUE OE THE BRITISH 
Coil A. Coil B. 
Mean radius. 236’31 236*02 
Mean of both. 236*16 
or nearly one part in 2000 less than before. Of the two values, it would appear that 
the latter is more likely to represent the actual condition of the coil during the 
spinnings, and. is therefore entitled to greater weight. If we give weights in the 
proportion of two to one, we get 
Mean radius=23*619 centimsV 
We have 
in w r hich 
Calculation of GK. 
GK= 2nhi 2 a sin 3 a 
{ />2 7,2_^3 
sin 2 a cosh¬ 
er 
1 ft 9 . . ' 
i7 sm a 
a = mean radius =23*625 (1st measurement) 
b = axial dimension of section = 1*990 
c = radial dimension of section = 1*565 
n = total number of turns = 576 
2b '=distance of mean planes = 6*595 
sin a—a-^r \f (« 2 + b' 2 ) 
From these data we find 
log 2 tt% 2 = 6*81617 
log a =1*37337 
log sin 3 a = 1*98744 
log {...} = 1*99995 
log GK =8*17693 
But if we substitute the adopted value of a, i.e., 23*619 centims., w r e have by 
subtraction of *00011 
log GK =8*17682 
Calculation of L. 
We may write 
L = 16 2 X 1 8 2 (L 1 +L 3 +2M), 
where L l5 L 2 are the coefficients of self-induction of the two parts, and M the 
* [August, 1882. At the time of use the tape was compared with a measuring rod, which again has 
been compared with a standard metre verified by the Standards Department of the Board of Trade. Eor 
the purposes of this investigation the differences observed are altogether negligible. I may add that the 
clock with which the standard tuning-fork was compared (see p. 137 of former paper) was rated from 
astronomical observations.] 
