ASTRONOMY AND METEOROLOGY. 401 



cated to the Philosophical Magazine, April, 18GO, by R. P. Gray, the author 

 proposes to show that the luminosity of shooting stars cannot arise from 

 their reflecting the solar light after emerging from the earth's shadow; nor, 

 on the other hand, their sudden disappearance arise from their plunging into 

 that shadow. He enumerates the three current modes of accounting for the 

 luminosity of meteors: first, the aforesaid supposition that they are them- 

 selves opaque, but illuminated by solar radiation while exposed to it; sec- 

 ondly, that they are self-luminous, an opinion which all have now nearly 

 abandoned; thirdly, that they become incandescent upon plunging into the 

 earth's atmosphere, either by friction and the enormous condensation which 

 their rapid flight causes, or by absorbing oxygen, and parts of their sub- 

 stance thus becoming chemically changed, and thus exhibiting the usual 

 phenomena of combustion. The author then notices Sir J. Lubbock's paper 

 in the Philosophical Magazine for February, 1848, and endeavors to show 

 that ordinary shooting stars would be quite too far off for us to observe such 

 small bodies at even the minimum distance at which, at certain times and 

 places on the earth's surface, we know they can be seen, if merely illumi- 

 nated by solar light. 



M. Julias Schmidt, in a communication recently read before the Imperial 

 Academy, Vienna, urges the importance of greater attention being paid to 

 the tails or luminous trains of light left by luminous meteors in their track, 

 sometimes remaining long after the meteors themselves have disappeared. 

 He considers these observations important : first, as regards their own proper 

 motion; secondly, the downward curvature sometimes exhibited by them, 

 and the way in which they break up and disperse; and, thirdly, the means 

 they may afford of ascertaining by parallax their height above the earth a 

 matter, too, of importance for determining at what height the atmosphere 

 ceases to have any influence. He observes, that an illustration of these tails 

 or trains may be obtained by throwing from you, quickly or slowly, a lighted 

 lucifer match, when just about to cease to burn; you will perceive either a 

 straight immovable line, or an undulating or a curling line, of whitish-gray 

 smoke standing in the air, if the air be calm or not in motion. 



NEW THEORY OF THE FORMATION OF COMETS AND METEORITES. 



The following theory, advocating the identity of comets and meteors, has 

 recently been advanced by Reichenbach, the well-known European scientist: 

 " Most meteorites," he says, " can be proved to be an aggregate of distinct 

 particles, inclosed in a dark mass or stroma. Each particle is, as it were, an 

 independent individual, and existed before the inclosing mass did being 

 an older meteorite inside of a younger, like a fossil shell in chalk. If we 

 conceive a space as large as the comet's tail originally filled with a gaseous 

 substance, in which the atoms of these particles were suspended, and if we' 

 furthermore conceive a tendency in these atoms to precipitate and crystal- 

 lize, it is clear that this process, going on at innumerable points at the same 

 time, milliards of crystals will form, each not much larger than the origi- 

 nal atoms, because the matter is taken up synchronously by all neigh- 

 boring crystals. These crystals by friction and pressure form larger par- 

 ticles, while the unequal distribution of the different elements and the action 

 of their forces Avill produce at some points denser aggregations than at 

 others, and from this results the phenomenon of one or more ' heads,' or 

 unclei. The process of condensation may continue, and the nucleus, at the 



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