DIELECTRIC CONSTANT OF WATER AT LOW TEMPERATURES. 227 
primary and secondary are in resonance, a comparatively 
great change in the effective length of the secondary is 
necessary to produce an appreciable change inthe deflection, 
but when the two circuits are put further out of resonance 
the deflections varied by a considerably greater amount for 
a given alteration of length of secondary. 
In order to determine the conditions under which the 
greatest change in deflection could be obtained for a given 
percentage change in the capacity of C, the detector being 
placed in the secondary circuit, a series of trials were 
made with an air condenser, consisting of two circular zinc 
plates, 30 cms. in diameter, the capacity of which was 
varied by altering the distance between the plates. In 
these trials a and b were given various values and asa 
result it was found that the highest degree of sensitiveness 
was obtained when a=b=A/8 approximately, the capacity 
being considerably too great to give good resonance. 
With this arrangement the slider was placed close to the 
condenser, but of course was practically equivalent to being 
about half way between the bridge and the middle of the 
circuit, i.e., half way between a node and a loop of the 
wave, and so the deflections obtained were really consider- 
ably smaller than if it could have been placed at the loop. 
A condenser with water as its dielectric was now attached 
to the wires in the position where the best results were 
obtained with the air condenser. Here a = b = 300 cms. 
and the slider was between a and c, and distant 5cms. from 
the latter point. This condenser consisted of two wires 
similar to the main wires, and each 25 cms. in length. 
These wires first ran horizontally towards one another and 
then were bent vertically downwards, at a distance vary- 
ing in different experiments from 9 to 11 cms. apart, dipping 
into water placed in a Jarge glass vessel. 
