450 
LORD RAYLEIGH AND MRS. H. SIDGWTCK ON THE 
when the [4] is excluded, r the resistance actually required during a set of measure¬ 
ments when [4] is connected, then the electromotive force actually compensating the 
action of [4] is E(1—r/p). 
At the beginning of the proceedings on March 29 the main current was stronger 
than that required for the simple compensation of E, so that to get a balance at the 
galvanometer the Leclanche’s would have had to be reversed. At 18 m from the 
commencement the current had fallen to the point of compensation with r=0. 
At 28 ra balance required r=20 B.A., at 34 m r=37, and at 4S m r=90. To take 
these observations, the easiest way is to overshoot the point somewhat, and then 
continually reversing the galvanometer to note the time of passing through the 
balance. From the curves representing the current weighings, the double force of 
attraction at the above times were found to be '9645, '956, '9495, '931, expressed in 
grams. This is what has been denoted by m (§ 26), and the corresponding current is 
i= '037048 *ym. 
§ 36. The resistance R between the points of derivation must be expressed in 
absolute measure, if we wish E to be so expressed. But for comparison with the 
results of other observers it will be convenient to keep this question apart and, in the 
first instance, to express our electromotive forces as if the B.A. unit were correct. 
Any factor (such as '9867) which may be adopted to express the B.A. unit in terms of 
the ohm will enter also into the expression of E in true volts. 
At the atmospheric temperature 13°'l the value of the [4] is 3'9998 B.A., whence 
R=4'00143 B.A., 
correction being made for the heating effect of the current. 
The formula for E is 
E='037048R.v/m.-^- 
p-r 
The value of p (on the occasion in question) was 4999 B.A., and this completes the 
data for the evaluation of E. The four values corresponding to the above observations 
are 
1-4559, 1'4553, 1'4553, 1'4566, 
giving as mean 
E=1'4558 B.A. volts. 
This result is for No. 4 at a temperature of 13 0, 1. The value of No. 4 in terms of 
No. 1 at the time in question was about "9998, so that we should have found for 
No, 1 
E= 1-4561 B.A. volts. 
We have still to reduce to the standard temperature of 15°. The coefficient 
originally given by Latimer Clark is 1'0006 per degree centigrade. Wright and 
