140 
PROFESSOR R. THRELFALL AND MR, J. H. D. BREARLET 
The temperature coefficient of specific inductive capacity, which would be required 
to compensate for the alteration of capacity, computed from the variation of the 
various dimensions with temperature, is 
y = + 1-89 X 10" 6 . 
This, of course, must be further investigated before we can regard it as a physical 
constant, but we may take it as pretty certain that there is either a temperature 
coefficient, or a strain coefficient, or both, or that the specific inductive capacity 
depends on the composition of the film, for the sulphur is partially annealed at 80° C., 
and, therefore, possibly at 70° C. It was a distinct oversight not to have tested this 
at the time by observing the capacity again when the sulphur was cold, and ulti¬ 
mately led to another experiment being undertaken for the special purpose of setting 
this question at rest. The result of this experiment was to prove that the specific 
inductive capacity of films, containing rather less insoluble sulphur than this, is dis¬ 
tinctly greater the more insoluble sulphur they contain. Hence the temperature 
coefficient must be greater than the above if it is at all affected bv the annealing-, for 
the annealing would almost certainly have reduced the capacity. 
While we used the old standard condenser the absorption was so great as to make 
the observations for capacity insufficiently exact for the present purpose. 
Section YI. 
The Determination of Specific Inductive Capacity of Varieties of Sulphur by the 
Method of Weighing. 
In the prosecution of these studies by one of us and Mr. J. B. Allen, some 
experiments were made on the specific inductive capacity of sulphur by the method 
of weighing. In these experiments a good many sources of electrification suitable 
for the purpose were investigated, and a good many causes of error detected and 
rectified. The results, however, only referred to one plate, i.e., to one containing 
6'7 per cent, of insoluble sulphur, and even these results were not in such good 
agreement as could be wished. The best way of preparing plates of sulphur had, 
however, been discovered, and we felt sure that by gradually improving the 
apparatus, we should ultimately succeed in obtaining reliable results. The great 
merit of the weighing method, however, from our point of view, is that it makes the 
resulting value of the specific inductive capacity absolutely independent of any 
electrical measurements whatever. In the experiments previously described, we 
relied on the constancy of the voltage of Clark cells, on standardized resistance 
coils, and on certificated condensers. It was now felt that an absolute determination 
of one of the constants ought to be made by a perfectly independent method, in order 
to supply as complete a check as possible on the previous work. No method could 
have met our ends more perfectly than the method of weighing, for the result 
