
Constant of Water at Low Temperatures. 657 
rT Pp 
condenser, and s the capacity per unit length of the two 
parallel wires. 
If the secondary is in resonance with the primary, 
change in the capacity of C will throw it out of resonance, 
and the deflexions produced by the detector will be smaller. 
An investigation of Morton’s formula shows that a given 
percentage ‘change of capacity produces the greatest propor- 
tionate change in the effective length of the circuit when 
a=b=\/8, the effect of the capacity being thus equivalent 
to an addition of X/2 to the length of the circuit. 
It has always been observed, however, that when the 
primary and secondary are in resonance a comparatively 
great change in the effective length of the secondary is 
necessary to produce an appreciable change in the deflexion ; 
but when the two circuits are not in tune, the deflexions vary 
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 deflexion results from a given percentage 
change in the capacity of C, a series of trials was made 
with an air-condenser consisting of two circular zinc plates 
30 centimetres in diameter, the capacity of which was varied 
by altering the distance between the plates. In these trials 
a and 6 were given various values, and as a result it 
was found that the highest degree of sensitiveness was ob- 
tained when a=)= . approximately, the capacity being much 
ral 
too large to give good resonance. 
With this arrangement the slider with the detector was 
placed close to the condenser, the detector was thus practically 
about halfway between the bridge and the middle of the 
circuit, i. e. halfway between a node and a loop of the wave, 
and so the deflexions obtained were really considerably 
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 centimetres, 
and the slider was between a and ¢ and distant 5 centimetres 
from the latter point. The condenser consisted of two wires 
similar to the main wires, and each 25 centimetres long. 
These wires first ran horizontally towards one another and 
then were bent vertically downwards at a distance varying 
in different experiments from 9 to 11 centimetres apart, 
dipping into water placed in a large glass vessel. 
With the water at the temperature of the room, the depth 
to which the wires were immersed was varied by i increasing 
Phil. May. S. 6. Vol. 7. No. 42. June 1904. 2 ¥ 
