ASSOCIATION UNIT OF RESISTANCE IN ABSOLUTE MEASURE. 
689 
The first column gives the number of the spinning, the first six being made with 
wire circuit open, and the last six with the wire circuit closed. In spinnings I., III., 
V., VIII., X., XII., the rotation was in the direction reckoned negative, and in the 
remaining ones positive. The second column gives the time, the third the reading of 
the auxiliary magnetometer, the fourth the reading of the principal magnetometer, the 
fifth the result of correcting the latter by the former 1 , the sixth and seventh the 
approximately constant sums and differences of consecutive pairs of numbers in the 
fifth column, and the eighth gives the mean deflection from zero, i.e., 5 29 for the open 
contacts, and 302‘56 for the closed contacts. 
The ninth column shows the results of the resistance Comparisons between the 
platinum-silver standard and the revolving copper coil before and after the closed 
contact spinnings. The first number (+ 212 ) means that at 8 h 36 m the resistance of 
the standard exceeded that of the copper by 212 bridge-wire divisions, each of which 
represents - 50 006 ' °f an ohm. It will be seen that during the spinnings the resistance 
of the copper increased, which accounts for the gradual fall observable in the seventh 
column. The mean of the comparisons before and after spinning is taken to correspond 
with the mean deflection 302'56. The three following columns show respectively the 
temperatures of the water in which the standard was immersed, of the air in the 
neighbourhood of the copper coil, and of the standard tuning-fork, while the thirteenth 
column gives the number of beats per minute between the electrically maintained and 
the standard fork. 
For the sake of more convenient comparison of the results obtained at the same speed 
on different nights, small corrections are calculated to reduce the actually observed 
deflections in the eighth column to what they Would have been in a standard con¬ 
dition of the resistance and of the speed. Under each of these heads we have two 
corrections to consider. In the first place the copper circuit differed in resistance 
from the standard coil by the outstanding (— 52) divisions of the bridge wire. The 
resistance of the whole being about 24 ohms, each division of the wire corresponds to 
one part in 480,000, so that in the present case the correction is additive and equal 
to 52 parts in 480,000, i.e., is equal to +”03 division of the scale. This is given in 
the fourteenth column. Secondly, the resistance of the standard itself depends upon a 
variable temperature. The mean temperature of the standard in this series was about 
13°, to which all the observations are reduced. In the present case the temperature was 
below the normal, so that the resistances were too small and the deflections too large. 
Accordingly the correction is negative. To estimate its amount the change of resist¬ 
ance with temperature is taken at three parts in 10,000 per degree ; so that in the 
present case we are to subtract 2 ’8 parts in 3000 of the whole deflection, i.e., ’27, 
as entered in the fifteenth column. With use of these corrections we obtain the 
deflection as it would have been observed had the resistance of the revolving circuit 
(together with the long copper bars by which it was connected with the bridge) been 
on every occasion exactly that of the standard at 13°. 
4 T 2 
