"If we suppose that the temperature of the sun at the present time is still increasing, or at least has been increasing until now, the glacial epoch can be easily accounted for. Formerly the earth had a high temperature of its own, but received a lesser quantity of heat from the sun than now; on cooling gradually, the earth's surface attained such a temperature as caused a great part of the surface of the northern and southern hemispheres to be covered with ice; but the sun's radiation increasing, the glaciers melted, and the climatic conditions became as they are now. In a word, the temperature of the earth's surface is a function of two quantities: one decreasing (the earth's own heat), and the other increasing (the sun's radiation), and consequently there may be a minimum, and this minimum was the glacial epoch, which, as shown by recent investigations, those of Luigi de Marchi (Report of _G. Schiaparelli, Meteorolog. Zeitschr._, 30, 130-136, 1895), are not local, but general for the whole earth" (see also M. Neumahr, _Erdegeschicht_).[68] Prof. Percival Lowell thinks that the life of geological palæozoic times was supported by the earth's internal heat, which maintained the ocean at a comparatively warm temperature.[69] The following passage in the Book of the Maccabees may possibly refer to an aurora-- "Now about this time Antiochus made his second inroad into Egypt. And it _so_ befell that throughout all the city, for the space of almost forty days, there appeared in the midst of the sky horsemen in swift motion, wearing robes inwrought with gold and _carrying_ spears, equipped in troops for battle; and drawing of swords; and _on the other side_ squadrons of horse in array; and encounters and pursuits of both armies; and shaking of shields, and multitudes of lances, and casting of darts, and flashing of golden trappings, and girding on of all sorts of armour. Wherefore all men besought that the vision might have been given for food."[70] According to Laplace "the decrease of the mean heat of the earth during a period of 2000 years has not, taking the extremist limits, diminished as much as 1/300th of a degree Fahrenheit."[71] From his researches on the cause of the Precession of the Equinoxes, Laplace concluded that "the motion of the earth's axis is the same as if the whole sea formed a solid mass adhering to its surface."[72] Laplace found that the major (or longer) axis of the earth's orbit coincided with the line of Equinoxes in the year 4107 B.C. The earth's perigee then coincided with the autumnal equinox. The epoch at which the major axis was perpendicular to the line of equinoxes fell in the year 1250 A.D.[73] Leverrier has found the minimum eccentricity of the earth's orbit round the sun to be 0·0047; so that the orbit will never become absolutely circular, as some have imagined. Laplace says--