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Page:Popular Science Monthly Volume 39.djvu/358

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MUCH has lately been heard about the "meteoritic theory" as an explanation of the origin and construction of the heavenly bodies. This hypothesis, now generally ascribed to Prof. Lockyer, seems to have been first suggested by the German astronomer Meyer. His theory has met with some support from Helmholtz, Proctor, Thomson, and Tait in Europe, and from Profs. Newton and Wright in America. Prof. Lockyer has recently published a full exposition of his theory in an elaborate and interesting work entitled The Meteoritic Hypothesis: a Statement of the Results of a Spectroscopic Inquiry into the Origin of Cosmical Systems. In this volume the author has worked out his hypothesis in great detail, and, as his theory has recently met with much adverse criticism, a brief review of the principal facts and arguments advanced by Lockyer, and also by his opponents, may prove of interest both to those who accept and those who reject his views.

Lockyer commences his work with an account of the falls of meteoric stones recorded in history. The earliest of these dates back so far as 1478 b. c., but, of course, with some uncertainty. Numerous well-attested falls are, however, referred to, and many of these meteorites are preserved in museums, one weighing over three tons being deposited in the British Museum. This fell at Cranbourne, Australia.

The general form of these meteoric stones is fragmentary, indicating that they are the fractured portions of larger masses, burst asunder by the force of the explosion which usually accompanies these interesting phenomena. In the case of the meteorite which fell at Butsura in 1861, pieces picked up at places three or four miles apart could be actually fitted together to form the original mass.

Meteorites are generally covered by a black crust, clearly caused by the intense heat developed by the mass in rushing through the earth's atmosphere with a planetary velocity.

Meteorites are generally composed of well-known terrestrial elements. Among these may be mentioned iron, nickel magnesium, manganese, copper, carbon, sulphur, etc. Some of them, however, contain mineral compounds which are "new to our mineralogy," such as compounds of sulphur and calcium, sulphur with iron and chromium, etc. Some meteorites contain a large quantity of hydrogen gas, which has been absorbed or "occluded"; others contain carbonic-acid gas. Some are composed chiefly of iron, others mostly of stony matter.