[Footnote 138: "Positive Philosophy," vol. i. p. 206.] [Footnote 139: "Philosophy of Aristotle," p. 66.] [Footnote 140: Prof. P. G. Tait, M.A., opening Address at the Edinburgh Meeting of the British Association of Science, in _Nature_, vol. iv. p. 271. See also Prof. Maxwell's Address at the Liverpool Meeting, in _Nature_, vol. ii. p. 422.] [Footnote 141: Miller's "Testimony of the Rocks," p. 221.] [Footnote 142: Sir William Thomson supposes that temperature to have been at least 7000° Fahr. See Thomson and Tait's "Natural Philosophy," vol. i. p. 716.] [Footnote 143: "Fragments of Science," p. 158.] [Footnote 144: Thomson and Tait, "Natural Philosophy," vol. i. p. 714. Winchell, "Sketches of Creation," p. 407.] [Footnote 145: Mayer, "Celestial Dynamics: Correlation and Conservation of Forces," p. 315. The palæobotanist Heer has described many species of tropical plants from Greenland, Alaska, and Spitzbergen.] [Footnote 146: Thomson and Tait, "Natural Philosophy," vol. i. p. 714. Observations on over forty artesian wells in Central Alabama show an average increase of temperature of 1° for every 47 feet of descent.--Dr. Winchell, in "Proceedings of American Association," part ii. p. 102.] [Footnote 147: Thomson and Tait, "Natural Philosophy," vol. i. p. 714.] [Footnote 148: Pouillet estimates that the heat which reaches the surface of the earth from its interior at 200 cubic miles per diem. A cubic mile is the quantity of heat necessary to raise a cubic mile of water 1° Centigrade in temperature.] [Footnote 149: Thomson and Tait, "Natural Philosophy," vol. i. p. 716.] [Footnote 150: Thomson and Tait, "Natural Philosophy," vol. i. p. 721.] [Footnote 151: See Winchell's "Sketches of Creation," chap. xxxvi.] [Footnote 152: Proctor, "Other Worlds than Ours," p. 193. "More likely these have been totally absorbed by the lunar rocks."--Dr. Winchell.] [Footnote 153: "Correlation and Conservation of forces," p. 245.] [Footnote 154: _North American Review_, Oct., 1861, pp. 372-3.] [Footnote 155: Mitchell's "Planetary and Stellar Worlds," p. 143.] [Footnote 156: Tyndall, "Fragments of Science," p. 135.] [Footnote 157: Quoted by Mayer, "Celestial Dynamics: Correlation and Conservation of Forces," p. 271.] [Footnote 158: "Outlines of Astronomy," p. 308.] [Footnote 159: Thomson and Tait, "Natural Philosophy," vol. i. p. 191.] [Footnote 160: Thomson and Tait, "Natural Philosophy," vol. i. p. 191. Balfour Stewart, "Treatise on Heat," p. 372.] [Footnote 161: Thomson and Tait, "Natural Philosophy," vol. i. p. 194; also Helmholtz, in "Correlation and Conservation of Forces," p. 242.] [Footnote 162: Winchell, "Sketches of Creation," p. 422. If the whole solar radiation were employed in dissolving a layer of ice inclosing the sun, it would dissolve a stratum ten miles and a half thick in one day.] [Footnote 163: Helmholtz, "Correlation and Conservation of Forces," p. 245.]