DIELECTRIC CONSTANT OF WATER AT LOW TEMPERATURES, 229 
produced by this detector on a second magnetometer were 
observed. These deflections should have been constant, 
but of course varied considerably with the spark. With 
the secondary circuit unchanged, when a series of readings 
were taken, although the deflections produced by either 
detector varied considerably, the ratio of the two deflec- 
tions was found to vary to a considerably less extent. 
In the following table is given a set of four readings of 
deflections of primary and secondary detectors and the 
ratio of the two, no change being made during the four 
readings :— 
op ds | 1000 ds/dp 
d1°5 28°7 St 
oll 33°95 903 
o4°4 31°8 924 
o2°9 200 Sit 
op being the deflection produced by the detector in the 
primary circuit, and és the deflection produced by the 
detector in the secondary. 
Accordingly in subsequent experiments, the deflections 
produced by detectors in both primary and secondary were 
taken after each spark, and the variation of the ratio of 
the two observed. These experiments all showed an un- 
doubted continuous fall in capacity as the temperature rose, 
there being no critical point at 4° C. 
In order to ascertain the extent of the change of capacity 
a condenser consisting of two circular brass plates, 30°2 
cms. in diameter and °755 ems. thick, which could be moved 
apart in a direction perpendicular to their planes, was sub- 
stituted for the water condenser, and observations were 
taken with the plates at different distances apart. The 
capacities at these distances were calculated by Kirchhofi’s 
formula: (Abhandl. p. 112.) 
