Page:The fairy tales of science.djvu/126

 and light, let us now examine some of the effects of heat.

The present condition of our earth is directly dependent upon the amount of heat we receive from the sun. If it were possible to move this planet nearer that orb, the quantity of heat would be much increased, and all the present races of plants and animals must perish; the same result would happen were the two bodies to be separated by a greater distance, owing to a deficiency of the genial influence. In the former case the world would be much too hot to hold us, and in the latter we should be regularly frozen out!

The rays that are emitted from the sun are partly absorbed by the atmosphere, which acts as a screen, and shields the earth's inhabitants from the full and perhaps destructive influence of the sun's heat. The quantity of heat received by us in one year is prodigious, for it has been calculated that it would suffice to melt a shell of ice forty-six feet thick, and covering every part of the globe. The heat-rays striking the earth, become dispersed in a variety of ways. Some are reflected, others are absorbed. Some of the rays warm the earth, and then warm the overlying air, and expanding it, rise with it to the upper regions of the atmosphere. But by far the greater number of heat-rays penetrate the earth, and descend to a considerable depth. In winter this stored-up heat partly returns to the surface, and ultimately becomes dissipated into the air, and from the air into infinite space.