In the first place, the sun's direct influence is exerted, on an equal portion of the globe at all times; which influence is felt, on the external surface, only where it is directly exerted. In such places it is felt intensely, but from the free action of the external atmosphere, so soon as that influence is withdrawn the heat escapes and flies off rapidly, generating cold in its passage, or by evaporation as we express it. Those parts of the external world from which the influence of the sun is withdrawn for the greatest length of time thus become intensely cold, excepting in the immediate vicinity of the polar openings, where the issue of warm air, from the internal cavity, tempers the atmosphere: but at a short distance from the verge of the opening the very influence of this warm air generates cold, by parting rapidly with its latent heat and condensing into snow and hail, which causes the circle of ice between the 70th and 80th degrees of latitude, called the "icy hoop." This escape of heat from the warm air which issues from the internal world, is so great as to irradiate the atmosphere near the polar openings; and in the extreme cold of winter, during the absence of the sun, this irradiation is so vivid as to be visible fifty degrees towards the equator, where the inhabitants, being fond of simple names, call it Aurora Borealis. On the other hand, as an equal portion of the globe is at all times acted upon directly by the sun's rays, the internal contents of that globe must be always subject to the same degree of heat, excepting such variations as may be occasionally produced by the direct rays of the sun admitted through the polar openings. Of this fact we had evidence on the external world, where, in the most intense cold weather, we had but to penetrate a short distance into the earth to escape its influence. The temperature of mines, dug a short distance into the earth, was always above the freezing point; and the degree of heat at a given distance below the general surface of the earth, was found to be nearly the same in all latitudes, and at all seasons. Hence what he called the innate warmth of the earth, was nothing more than the collected heat of the sun absorbed and retained by the globe from the continued action of that luminary upon an equal proportion of it, at all times, in the same manner as a glass globe full of water, when set before a fire, will absorb and diffuse heat throughout the contents of the vessel equally, although but one side is exposed to the direct influence of the fire, while that part of the external surface of the vessel which is not exposed to the fire, but is subject to the influence of the cold air of the room, will obtain no other heat than may be communicated by the fluid within.