Page:Popular Science Monthly Volume 47.djvu/325

Rh except by supposing our earth solid (or very thick in crust), cooling and contracting unequally.

As to other arguments for the fluidity of the earth, we have seen that volcanic phenomena carefully studied go against the idea of one central reservoir for the lavas. It is, of course, natural to think of a cooling globe as having a solid crust and molten interior, but it is quite possible that solidification started at the center, just as even now in the nebulous stars the condensation from gaseous to liquid state proceeds from central points or nuclei.

We may say, then, in summing up, that there are no valid arguments against the conclusion to which all the facts point, that the earth is at heart an intensely hot but practically solid mass of iron.



N the divisions of land and water, the situations of the continents, the seas, and the islands in the seas; the mountain ranges and the rivers which have their sources in them; the elevations and depressions of the more even surfaces, together with procession of the seasons and the earth's diurnal revolutions, we have some of the conditions for a great variety of climates. Proceeding from the equator toward the poles or moving along the surface of the earth in any direction, man, who seems to be the toughest animal on the face of the earth, can so adjust himself to varying climatic conditions as to exist in fairly good health almost anywhere, from the steaming equatorial jungles to the regions of perpetual ice and snow, as well as in intermediate locations where often heat and cold vary from one extreme to the other in rapid succession. And yet men live and thrive in nearly all lands and under the most diverse conditions, and with intelligent self-adjustment to their environment they may live well and live out their allotted times as a general rule. While the human race is exceedingly flexible, and can adapt itself rapidly to very diverse conditions, such adaptations, be they rapid or relatively slow, are not accomplished without an expenditure of energy to correspond with the functional modifications thus brought about. We call the process acclimatization, and the person, after subjection to the process, we say is acclimatized. That is to say, the functional activities of such a person have become adjusted to his environment; his functions have learned to harmonize with the