FORCE OF THE WESTON NORMAL CELL IN SEMI-ABSOLUTE VOLTS. 
179 
would be changed by less than 5 parts in 1,000,000 through neglecting the last two 
terms, if we assumed, for example, that x was as much as half a millimetre, y 1 a 
twentieth of a millimetre, and y 2 a tenth of a millimetre. 
It is thus quite apparent, considering this discussion in conjunction with the 
experimental tests on the variations of T for resettings of the cylinders (both in 
rotated and reversed positions), that B can be determined satisfactorily in this way. 
During the deflection experiments the suspensions carried a current of half an 
ampere. The following observations on the period illustrate the constancy under these 
conditions. 
The figures below marked with an asterisk represent the mean of the two values 
obtained when the current flowed through the suspended system, first in one direction 
and then in the other. 
Table XVI. 
Period. 
seconds. 
I. No current flowing .. 
11-6672 
Current of half an ampere. 
*11-6669 
No current flowing. 
11-6669 
Current of half an ampere. 
*11-6669 
II. (Slight change in weight of system.) 
No current flowing. 
11-6571 
Current of half an ampere. 
*11-6574 
No current flowing. 
11-6575 
Current of half an ampere. 
*11-6573 
III. May 5. 
11-6566 
„ 28. 
11-6564 
June 3 . 
11-6564 
„ 13. 
11-6564 
IV. (Moment of inertia changed.) 
August 2. 
6-5659 
November 14. 
6-5652 
The temperature of the dynamometer was about 20° C. during all recorded 
observations for T, but the clamping connections at the supports were of such a nature 
that B was nearly compensated for temperature changes. 
(g) The Value of B during the Deflection Observations. 
Observations for T l5 T 2 , d u and d 2 , were taken immediately before and after the set 
of deflection readings for the current measurement. As the repetition of the various 
sets of deflections took several weeks, it was necessary to test the constancy during 
these observations. This was done by several determinations of T, at a temperature 
of 20° C. 
2 a 2 
