During this period of the voyage, Captain Nemo made some interesting experiments on the varied temperature of the sea, in different beds. Under ordinary conditions these observations are made by means of rather complicated instruments, and with somewhat doubtful results, by means of thermometrical sounding-leads, the glasses often breaking under the pressure of the water, or an apparatus grounded on the variations of the resistance of metals to the electric currents. Results so obtained could not be correctly calculated. On the contrary, Captain Nemo went himself to test the temperature in the depths of the sea, and his thermometer, placed in communication with the different sheets of water, gave him the required degree immediately and accurately.

It was thus that, either by overloading her reservoirs or by descending obliquely by means of her inclined planes, the Nautilus successively attained the depth of three, four, five, seven, nine, and ten thousand yards, and the definite result of this experience was that the sea preserved an average temperature of four degrees and a half at a depth of five thousand fathoms under all latitudes.