MR. W. CASSIE ON" THE EFFECT OF TEMPERATURE ON 
Values of rate of change corrected for instantaneous charge. 
44° C. -00037 
57 -00043 
63 -00048 
Fig. 4. 
Electrostatic Ohservations .—In the observations on ebonite by the electrostatic 
method the condenser consisted of two sheets of ebonite between the iron discs, and 
with a copper disc between them. The condenser rested upon a glass tripod inside 
the air bath, and the leading wires entered the air hath through glass tubes. The 
capacity of this was adjusted so as to be within the range of a fine sliding condenser in 
the Laboratory against which it was balanced; and the readings were taken on an 
Elliott electrometer. It required great care and patience to make so slow an electro¬ 
meter suffice, for the reasons already stated. The insulation of all parts of tlie 
apparatus also required much attention. 
The cold temperature, 8°, was obtained by running iced wafer round the bath 
containing the condenser. Subsequent observations showed that this had affected 
the insulation and so increased the apparent diminution of capacity. 
The greater rate of change shown by the electrostatic results is probably due to 
the time of charging by the key worked by hand being greater than with the tuning 
fork. 
Any leak would produce an apparent decrease of capacity by this method ; so that, 
although the electrostatic results are of less weight than the others, the agreement of 
the results of two methods in which the main source of error tends in opposite 
directions is a confirmation of their accuracy. 
The electrostatic results are given in the following table :— 
Temperature. 
Rate of cEange of 
capacity per degree. 
17° C. 
40 
-0008 
48 
-0010 
50 
-0016 
57 
-0015 
(8 
-0021) 
