302 
LORD RAYLEIGH AND MRS. H. SIDGWICK ON THE ABSOLUTE 
multiple arc whose terminals rest in these cups. The galvanometer terminals are led 
into two other cups B and C. The ends of these are beaten flat and the legs of the 
Yy rest upon them. The connexion between C and D was through a stout copper 
rod, which may be regarded as part of c. For the first series the connexion between 
A and B was through a single coil of 10 units’ resistance, replaced in subsequent series 
by other coils giving altogether 16 and 20 units’ resistance respectively. 
To make the necessary adjustment and variation of resistance, a box, E, was placed 
in multiple arc with the two unit coils. The resistances taken from the box were 
afterwards carefully determined, but they enter into the final results in quite a 
subordinate manner. 
§ 13. Further trials now led to the satisfactory conclusion that the defect was 
remedied, for the means obtained on different days agreed well together, even although 
the resistance coils were taken down and remounted in the interval. As we had now 
every reason to suppose that our experiments would have a successful issue, we pro¬ 
ceeded to make the final adjustments preparatory to a complete series of observations. 
In the first and second series the two coils were near one another, separated only 
by three slips of glass, and held firmly together by wooden clamps. The adjustments 
presented no particular difficulty. By means of an iron finger clamped to the disc 
and carried gradually round, it could be verified that the coils and disc were concen¬ 
tric and in parallel planes. The coils were gradually wedged into their places, and 
secured when their mean planes occupied the desired symmetrical positions relatively 
to the disc. It is evident that errors of maladjustment influence the result only in 
the second order. 
§ 14. Experience in this series having shown that the arrangement was satisfactory, 
and that the sensitiveness was fully sufficient, we proceeded to make a second series 
of observations without displacement of the induction coils, but at a speed of rotation 
lower than before in about the ratio of 16 : 10. This, of course, entailed a corre¬ 
sponding change in B, which was effected by increasing the component c. An 
agreement between the final results of the two series would give an important con- 
