The author described the results of a number of experiments, made during the examination of the “Challenger” Deep-Sea Thermometers, with the view of testing, at pressures of 3 tons weight per square inch and upwards, Thomson's formula for the heat developed by compression (Proc. Roy. Soc., 1857, p. 568).

When, for instance, the bulb of one of the thermometers was surrounded by a shell of lard upwards of half an inch thick, the total effect produced by a pressure of 3½ tons weight was 5° F.; while for the same pressure, without the lard, the effect was only l°·8 F. The temperature of the water in the compression apparatus was 43° F., so that the temperature effect due to the compression of water was less than 0°·2 F. In obtaining this number it was assumed from Kopp's experiments that the coefficient of expansion of water at a temperature t° C., near its maximum density point (roughly, 4° C.), . Hence the effect due to the compression of the lard was 3°·4 F., or about 1° F. per ton weight. This is subject to corrections (which will increase its value) depending on the heat developed by friction in the pump and in the narrow connecting tubes, and on another cause not yet fully ascertained.