VEBDET’S CONSTANT IN ABSOLUTE UNITS. 
13 
Also noting that 2£ / =l*04, 
r / 3 =(18-10 2 4-0-52 2 )i=log- 1 3*7735723. 
Now S(A)'=67 ref, where c t is the mean radins of the coils. 
Now the diameters of the coil are 
Internal 
External . 
. 4*815 inches*, 
. 4*950 „ 
which give a mean radius 
c,= 6*201 centims.; 
whence D(A)'=log 1 2*8602118. 
From (17) we have, then, 
(18) 
and 
2(A) = 77280*5. 
From these same experimental data Prof. Maxwell made a calculation, from which 
he found 
2(A)=77554*0 
Prof. Maxwell’s Experiments with the large Dynamometer. 
In these experiments the helix and dynamometer were placed exactly concentric. A 
magnet and mirror was suspended rather more than a metre distant from them, first in 
front and then behind, so as to correct any error in centering, and varying currents were 
sent opposite ways till there was no deflection. 
At this distance the helix and dynamometer could each be considered to be replaced 
by their equivalent magnetic discs, and the difference between r and r l may be neglected 
in comparison with those quantities themselves. 
The formula for 2(A) then becomes 
2(A)=gs(A)'. 
Where there was no action on the suspended magnet, Prof. Maxwell found 
Now the area 2(A)' of the great dynamometer is 
870200 sq. centims. 
* These measurements were made by Messrs. Elliott. 
