Page:Journal of the Royal Geographical Society of London, Volume 1 (2nd edition).djvu/242

214 character, of the discussions which are yet involved in the results of former experiments, and of the light which they assist in throwing on the temperature of the globe and the theory of the earth. The observations made during the expedition of the Blossom were with self-registering thermometers, at various depths, from 50 to more than 700 fathoms; and in all cases it appears that the temperature diminishes with the depth to a certain distance, when it begins to increase again, or at least remains stationary; and this depth appears to vary from 300 to 500 fathoms. The experiments at depths beyond this were too few to allow of any satisfactory results; but it appears, as in the experiments of the Russian expedition recorded by Lentz, that below 400 fathoms the temperature was nearly stationary. The difference of temperature between the surface and a depth of 700 fathoms, as observed by Captain Wauchope, in H.M.S. Euryene, amounted to 31°. There are several experiments made by Captain Beechey, in which the difference amounted to 35°, 36°, and 37°, and in one case to 39°.5; this was at a depth of 400 fathoms. At 784 fathoms in the North Pacific, the difference was 36°.8; and in the same place, at 600 fathoms, 37°; at 760 fathoms, the difference was 35°.5; and in the same place, at 575 fathoms, 35°. In the South Atlantic, at a depth of 854 fathoms, the difference was only 10°.4.

—The observations on terrestrial magnetism were on the dip of the magnetic needle, on the intensity of the magnetic force, and on the variation of the compass with Barlow's plate attached. The dips were observed with the same instrument which had been used at Melville Island: it had two common needles, and another with a moveable weight, fitted up on Professor Mayer's principle. No. 1 was used solely for observations on the magnetic intensity, and its poles consequently were never reversed; while No. 2 and Mayer's were employed for dips, and had their poles changed at each observation. The horizontal needle was suspended in a stirrup by a fine silk, in an octagon wooden box, furnished with a graduated wooden circle on the inside, and covered with a glass top, in which there was fitted a contrivance for moving the needle out of the magnetic meridian. Until the arrival of the ship at Woahoo, the stay at each place was too short, and Captain Beechey's time was too much occupied with astronomical observations, and with the business of surveys, for him to give the necessary attention to these delicate observations; but after that period the observations were regularly made. Unfortunately for the completion of the series upon the magnetic intensity, the needles used for that purpose became corroded upon the passage from Loo Choo to Petropaulski, by which their magnetic power was much diminished; and as the amount of the change