56 PROFESSOR C. V. BOYS ON THE 
tion under Operations 12 and 13; certainly not 1, and not, apparently, +1 unit. 
From this it will be evident that since 
(3) + (4)=1, 
(4) =0, 
(2) + (4) =0, 
(2) = 0, (8) =1, and (4) =0. Therefore 1 unit must be subtracted from the 
observed deflection of Operation 10 in all experiments after No. 3. It is for this 
reason that the numbers under P in Table I., p. 63, differ very slightly from the 
observed deflections. 
2. The Geometry of the Apparatus. 
In this part of the calculation I find the exact relative positions of the several 
oravitating bodies, from which the couple twisting the fibre may be found in terms of 
G. Thus, the couple = QG. As before, the process followed will be most readily 
explained by giving an example. 
