( 376 ) 
[May, 
PROCEEDINGS OF SOCIETIES. 
Royal Society, April 3. — “On the Thermal Conductivity of 
Water,” by J. T. Bottomley. The experiments described in this 
paper were conducted by a method devised by Sir William 
Thomson. The liquid whose thermal conductivity was to be 
determined was heated from above, to avoid convention cur^nts. 
Two methods of heating have been used. In one, a horizontal 
steam chamber was applied at the top of the water or other 
liquid, and, steam being continuously passed through the heating 
chamber, the surface of the liquid under experiment was kept at 
a very high temperature, and heat was conducted from above 
downwards. In the other method a large quantity of very hot 
water was deposited on the top of a mass of cold water, mixing 
being prevented by a simple contrivance, and the heat of this 
superincumbent layer was conducted downwards through the 
colder water below. The experiments were carried on in very 
large vessels, or tanks, in order to avoid disturbance by means 
of loss of heat at the sides. Three principal thermometers were 
employed ; together with a fourth, whose objeCt was merely to 
show when heat begins to be lost at the bottom of the layer of 
fluid experimented on. When this loss commences the experi- 
ment is at an end. The other three thermometers were used 
thus : — First there was a thermometer with a bulb 30 centims. 
long, which was placed vertically, its objeCt being to show the 
average temperature from top to bottom of the layer of fluid 
bounded by horizontal planes passing through the top and bottom 
of its bulb. The rise of this thermometer in any time shows 
the quantity of heat that has passed into the stratum occupied 
by it in that time. The other two thermometers were placed 
with their bulbs horizontal, and one at a known distance verti- 
cally above the other. They indicate the temperatures of the 
layers in which they are placed. Knowing the difference of tem- 
peratures of two sides of a stratum of a liquid during any time, 
and the quantity of heat conducted across the stratum during 
that interval of time, the thermal conductivity of the liquid can 
be calculated. The result arrived at by the experiments described 
is that the thermal conductivity of water may be taken at from 
0*0022 to 0*00245 in square centimetres per second. The author 
has made some experiments on the thermal conductivity of so- 
lution of sulphate of zinc. These experiments are now being 
carried on with the assistance of a grant from the Government 
Fund of £4000. 
