METEORIC STONES AND SHOOTING STARS. 



through the terrestrial atmosphere and be drawn down upon 

 the surface by the earth's attraction. 



By admitting the possible existence of a swarm of such bodies 

 consisting of many hundreds, or even thousands, against which 

 there is no physical impossibility, not to say improbability, a 

 satisfactory explanation is afforded of the most extraordinary 

 phenomena of meteoric showers that have ever been witnessed 

 or recorded. 



8. Such are the various theories which have been offered to 

 explain the phenomena attending meteoric stones and shooting 

 stars. The evolution of light which attends their rapid progress 

 through space has been accounted for in all of them in the 

 same manner. It is supposed that, in the rapid motion with which 

 the body proceeds, the air which lies in its path is so extremely 

 condensed, as either to become itself luminous, or to acquire so 

 intense a heat as to render the stone incandescent, or, perhaps, 

 to produce upon it a superficial combustion, the signs of which 

 are exhibited in the blackness and elevated temperature of 

 its surface. This reasoning is supported by the well-known 

 experiment of the fire-syringe. In that instrument a solid 

 piston is fitted in a cylinder, so as to be air-tight, carrying 

 a piece of amadou or other easily combustible matter, at its 

 end. When the piston is suddenly forced down, so as to 

 produce an instantaneous and severe compression of the air 

 under it, the amadou takes fire, and, if the cylinder be glass, 

 a flash of light is visible through it. It has therefore been 

 contended, that in this experiment the air under the piston 

 has acquired, by compression, such a temperature as renders 

 it luminous. 



More recent experiments, however, made in France, throw 

 doubt upon the validity of this inference. It is said that the 

 unctuous matter commonly used to lubricate the piston in the 

 fire-syringe is, in fact, the source of the ignition ; for that, when 

 experiments were made with pistons not so lubricated, the flash 

 of light was not produced. It is, therefore, considered not to be 

 satisfactorily proved, that air by such mechanical compression 

 has become luminous. Still, however, it may be contended 

 that, even though the air were not to become luminous, 

 it may, nevertheless, be raised to such a temperature by com- 

 pression as, by contact with the meteorite, may render the 

 latter luminous. 



Admitting the possibility of this supposition, as applied to 



the air contiguous to the earth, or at any moderate elevation, a 



difficulty has been raised from the vast height at which meteorites 



have been visible. By barometric experiments and observations 



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