File:Astronomy for the use of schools and academies (1882) (14577717549).jpg

Identifier: astronomyforuseo00gill (find matches)
Title: Astronomy for the use of schools and academies
Year: 1882 (1880s)
Authors: Gillet, J. A. (Joseph Anthony), 1837-1908 Rolfe, W. J. (William James), 1827-1910
Subjects: Astronomy
Publisher: New York : Potter, Ainsworth, & Co.
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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Fig. 350. cutting instruments. It always contains eight or ten per centof nickel, together with small quantities of cobalt, copper, tin,and chromium. This composition has never been found inany terrestrial 17^ineral. Aerolites also contain, usually insmall amount, a compound of iron, nickel, and phosphorus,which has never been found elsewhere. 308 ASTRONOMY. Meteorites often present the appearance of having beenfused on the surface to a slight depth, and meteoric iron isfound to have a peculiar crystalline structure. The externalappearance of a piece of meteoric iron found near Lock-port, N.Y., is shown in Fig. 350. Fig. 351 shows the peculiarinternal structure of meteoric iron. 308. Meteoroids. — Astronomers now universally holdthat shooting-stars, meteors, and aerolites are all minutebodies, revolving, like the comets, about the sun. They
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are moving in every possible direction through the celestialspaces. They may not average more than one in a millionof cubic miles, and yet their total number exceeds all calcu-lation. Of the nature of the minuter bodies of this classnothing is certainly known. The earth is continually en-countering them in its journey around the sun. They areburned by passing through the upper regions of our atmos-phere, and the shooting-star is simply the light of thatburning. These bodies, which are invisible till they plungeinto the earths atmosphere, are called meteoroids. 309. Origin of the Light of Meteors. — When one of ASTRONOMY. 309 these meteoroids enters our atmosphere, the resistance ofthe air arrests its motion to some extent, and so convertsa portion of its energy of motion into that of heat. Theheat thus developed is sufficient to raise the meteoroid andthe air around it to incandescence, and in most caseseither to cause the meteoroid to burn up, or to dissipate itas vapor. The lumino

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