Outlines of the Earth's History: A Popular Study in Physiography

by Nathaniel Southgate Shaler

As they come to us these meteorites often break up in the atmosphere, the bits being scattered sometimes over a wide area of country. Thus, in the case of the Cocke County meteorite of Tennessee, one of the iron species, the fragments, perhaps thousands in number, which came from the explosion of the body were scattered over an area of some thousand square miles. When they reach the surface in their natural form, these meteors always have a curious wasted and indented appearance, which makes it seem likely that they have been subject to frequent collisions in their journeys after they were formed by some violent rending action.

In some apparent kinship with the meteorites may be classed the comets. The peculiarity of these bodies is that they appear in most cases to be more or less completely vaporous. Rushing down from the depths of the heavens, these bodies commonly appear as faintly shining, cloudlike masses. As they move in toward the sun long trails of vapour stream back from the somewhat consolidated head. Swinging around that centre, they journey again into the outer realm. As they retreat, their tail-like streamers appear to gather again upon their centres, and when they fade from view they are again consolidated. In some cases it has been suspected that a part at least of the cometary mass was solid. The evidence goes to show, however, that the matter is in a dustlike or vaporous condition, and that the weight of these bodies is relatively very small.

Fig. 2.—The Great Comet of 1811, one of the many varied forms of these bodies.

Owing to their strange appearance, comets were to the ancients omens of calamity. Sometimes they were conceived as flaming swords; their forms, indeed, lend themselves to this imagining. They were thought to presage war, famine, and the death of kings. Again, in more modern times, when they were not regarded as portents of calamity, it was feared that these wanderers moving vagariously through our solar system might by chance come in contact with the earth with disastrous results. Such collisions are not impossible, for the reason that the planets would tend to draw these errant bodies toward them if they came near their spheres; yet the chance of such collisions happening to the earth is so small that they may be disregarded.

Motions of the Spheres.

Although little is known of the motions which occur among the celestial bodies beyond the sphere of our solar family, that which has been ascertained is of great importance, and serves to make it likely that all the suns in space are upon swift journeys which in their speed equal, if they do not exceed, the rate of motion among the planetary spheres, which may, in general, be reckoned at about twenty miles a second. Our whole solar system is journeying away from certain stars, and in the direction of others which are situated in the opposite part of the heavens. The proof of this fact is found in the observations which show that on one side of us the stars are apparently coming closer together, while on the other side they are going farther apart. The phenomenon, in a word, is one of perspective, and may be made real to the understanding by noting what takes place when we travel down a street along which there are lights. We readily note that these lights appear to close in behind us, and widen their intervals in the direction in which we journey. By such evidence astronomers have become convinced that our sphere, along with the sun which controls it, is each second a score of miles away from the point where it was before.

There is yet other and most curious evidence which serves to show that certain of the stars are journeying toward our part of the heavens at great speed, while others are moving away from us by their own proper motion. These indications are derived from the study of the lines in the light which the spectrum reveals to us when critically examined. The position of these cross lines is, as we know, affected by the motion of the body whence the light comes, and by close analysis of the facts it has been pretty well determined that the distortion in their positions is due to very swift motions of the several stars. It is not yet certain whether these movements of our sun and of other solar bodies are in straight lines or in great circles.

It should be noted that, although the evidence from the spectroscope serves to show that the matter in the stars is akin to that of our own earth, there is reason to believe that those great spheres differ much from each other in magnitude.

We have now set forth some of the important facts exhibited by the stellar universe. The body of details concerning that realm is vast, and the conclusions drawn from it important; only a part, however, of the matter with which it deals is of a nature to be apprehended by the student who does not approach it in a somewhat professional way. We shall therefore now turn to a description of the portion of the starry world which is found in the limits of our solar system. There the influences of the several spheres upon our planet are matters of vital importance; they in a way affect, if they do not control, all the operations which go on upon the surface of the earth.