
Constant of Water at Low Temperatures. 661 
the various temperatures. In all these curves there is to be 
noticed a decided fall in capacity as the temperature rose ; 
and ihe curves are practically straight lines. 
The change of capacity for 1° rise in temperature, expressed 
as a percentage of the capacity at 0°C., obtained from the 
different curves is : 
From fig. 3 ‘464 
Se Ge "478 
» fig. 9 28% 
7) A “O44 
The dielectric of the condenser consisted partly of air and 
partly of water, the wires being out of the water for a 
considerable part of their length; and as the variation 
affected only the water, the total percentage change of 
capacity is less than that of the dielectric constant of the 
water. 
In the first two trials recorded above the water was placed 
in a large glass vessel 25 centimetres square, and the depth 
of water in it was about 15 centimetres ; but in the other two 
the water was placed in a beaker 15 centimetres in diameter 
and the depth of water was about 15 centimetres: so in this 
case the air would have a greater relative share in the whole 
effect, and the observed change is less than in the former 
trials, where the variation in capacity is probably very nearly 
equal to the variation in the dielectric constant of water. In 
all four trials the wires were immersed to a depth of 5 or 
6 centimetres, and were from 9 to 11 centimetres apart. 
The assumption has been made that when the same 
deflexion is obtained with the water- and air-condensers, 
the capacities are the same. By removing water from the 
vessel, and so decreasing the capacity, we can come into — 
a position of resonance ; and it was found that the maximum 
deflexions obtained when this was done were practically the 
same as the greatest deflexions obtained with the air-con- 
denser, and so ‘the conductiv ity of the water has no appreciable 
effect and the above assumption is probably permissible. 
The specific conductivity of the water was measured, and 
found to be 3:7 x 10-® at 18°°8 C. 
These results show no indication of the large effect observed 
by Thwing at 4° C. With the exception of the results shown 
in fig. 5, all the observations are definitely lower at 4° than 
at 0°. According to Thwing the dielectric constant at 0° is 
719° 2 and at 4° 85° a0;,.t. e. it increases by 7:2 per cent. In 
fig. 3 the capacity at 0° is 16°39; if it were 7:2 per cent. 
higher at 4°, the capacity would be 17°51 at that temperature. 
