Another asks:
"How do you account for the fact that this Drift material does not resemble the usual aërolites, which are commonly composed of iron, and unlike the stones of the earth?"
I nave shown that aërolites have fallen that did not contain any iron, and that could not be distinguished from the material native to the earth. And it must be remembered that, while the shining meteoroids that blaze in periodical showers from radiant points in the sky are associated with comets, and are probably lost fragments of comet-tails, these meteoroids do not reach the earth, but are always burned out, far up in our atmosphere, by the friction produced by their motion. The iron aërolite is of different origin. It may be a product of space itself, a condensation of metallic gases. The fact that it reaches the earth without being consumed would seem to indicate that it belongs at a lower level than the meteoric showers, and has, consequently, a less distance to fall and waste.
And these views are confirmed by a recent writer,[1] who, after showing that the meteoroids, or shooting-stars, are very different from meteorites or aërolites, and seldom or never reach the earth, proceeds to account for the former. He says:
"Many theories have been advanced in the past to account for these strange bodies, but the evidence now accumulated proves beyond reasonable doubt that they are near relatives, and probably the débris of comets.
"Tempel's comet is now known to be traveling in the same orbit as the November meteors, and is near the head of the train, and it appears, in like manner, that the second comet of 1862 (Swift's comet) is traveling in the orbit of the August meteors. And the first comet of 1881 seems to be similarly connected with the April meteors. . . .
[1. Ward's "Science Bulletin," E. E. II., 1882, p. 4.]
{p. 398}
"Although few scientific men now question a relationship between comets and the ordinary meteors, there are those, and among them some of our ablest men, who think that the large meteors, or bolides, and aërolites, may be different astronomically, and perhaps physically, from the ordinary shooting-stars, and in the past some contended that they originated in our atmosphere others that they were ejected from terrestrial volcanoes. . . And at the present time the known facts, and all scientific thought, seem to point to the conclusion that the difference between them and ordinary shooting-stars is analogous to that between rain and mist, and, in addition to the reasons already given for connecting them with comets, may be mentioned the fact that meteorites bring with them carbonic acid, which is known to form so prominent a part of comets' tails; and if fragments of meteoric iron or stone be heated moderately in a vacuum, they yield up gases consisting of oxygen, carbon, hydrogen, and nitrogen, and the spectrum of these gases corresponds to the spectrum of a cornet's coma and tail.
"By studying their microscopical structure, Mr. Sorby has been able to determine that the material was at one time certainly in a state of fusion; and that the most remote condition of which we have positive evidence was that of small, detached, melted globules, the formation of which can not be explained in a satisfactory manner, except by supposing that their constituents were originally in the state of vapor, as they now exist in the atmosphere of the sun; and, on the temperature becoming lower, condensed into these "ultimate cosmical particles." These afterward collected into larger masses, which have been variously changed by subsequent metamorphic action, and broken up by repeated mutual impact, and often again collected together and solidified. The meteoric irons are probably those portions of the metallic constituents which were separated from the rest by fusion when the metamorphism was carried to that extreme point.'"