188 MR. A. NORMAN SHAW: A DETERMINATION OF THE ELECTROMOTIVE 
(Column 15.) 
(Column 16.) 
S. 
Mean S. 
Position III. - 
'84-8661 
84-349/ 
84-608 
84-3561 
84-861/ 
84-608 
'84-4501 
84-988/ 
84-720 
Position IV. - 
84-981 1 
84-448/ 
84-714 
The figures in the ninth column are obtained by applying the potentiometer 
correction to the mean of the two telescope readings; and the next column contains 
S which is obtained in the manner outlined above, by taking the difference of the 
middle reading from the mean of the first and last readings in each group. 
To facilitate comparison and to illustrate the accuracy in repetition of readings, the 
next four columns contain corrections for reducing S to its corresponding value for 
the following standard conditions t x — 23°T2 C., t 2 — 28°'0 C., d = 12'4448 cm., and 
(3 = 298'450 cm., these numbers being chosen because they differed but slightly from the 
average values and agreed with those occurring in the various auxiliary calibrations or 
standardizations. The fifteenth column gives S reduced to the value corresponding 
to these standard conditions, and the last column contains the figures for the mean S, 
from which the effect of H, the earth’s field, is eliminated. 
The temperature coefficient of 0'00025 is taken for the standard two ohms in 
calculating the correction due to t x , and 0'000018 is used for the two-tenths in 
correcting for t 2 . It is sufficiently accurate to assume that S is changed by the same 
percentage as the resistance in each case, but in the opposite direction. 
To obtain the correction due to d, it can easily be shown that for small differences 
a change of X per cent, in d means a change of 0'60 X per cent, in S in the opposite 
direction. 
A change in /3 means a proportional change in S. 
A summary of the value for the mean S for each of the different positions of the 
fixed coils is given below. The letters (a), ( b ), and (c), &c., represent a readjustment 
of the dynamometer and circuit. This involves a resetting of the fixed coils and 
general connections as well as the minor variations of condition recorded in the 
previous tables. As each position involves a resetting it will be seen that there are 
thus nine readjustments of the general conditions of the experiment, and it should be 
noted that the final mean involves 290 deflection readings. The controlling force of 
the suspensions and the position of the suspended coils were constant throughout the 
measurements. 
