METEORIC STONES AND SHOOTING STARS. 



any probable conjectures respecting their origin. And since it 

 is now established that no difference is observable between the 

 larger shooting-stars and small fire-balls, both having similar 

 altitudes and velocities, and presenting absolutely the same 

 appearances, we may assume them to be of the same nature, and 

 that whatever has been proved respecting fire-balls will apply 

 equally to the larger shooting-stars. Whether the meteoric 

 appearances to which the latter term is applied may not include 

 objects of totally different natures, is a question admitting a 

 doubt. It is possible that among the shooting-stars there may 

 be objects which are merely electric sparks, or which have their 

 origin in spontaneously-inflammable gases, known or unknown, 

 existing in the atmosphere ; but the greater part of them must 

 be considered as identical with fire-balls. 



9. The lunar hypothesis advanced by Laplace, Berzelius, and 

 others, to explain meteoric stones, appears to be attended with 

 serious difficulties, if, indeed, it be not altogether incompatible 

 with the phenomena of shooting-stars. In order to enter our 

 atmosphere with a velocity of 20 miles in a second, it may be 

 shown that, if they come from the moon, they must have been 

 projected from the lunar surface with a velocity of about 120,000 

 feet in a second, which may be regarded as almost impossible. 



It thus appears that those shooting-stars and fire-balls which 

 have the planetary velocity of from 20 to 40 miles in a second, 

 cannot, with any probability, be regarded as having their origin 

 in the moon. Whether any individual bodies, moving with a 

 smaller velocity, may have a lunar origin, is a question which 

 cannot be decisively answered. " To me," says Dr. Olbers, " it 

 does not appear at all probable ; and I regard the moon, in its 

 present circumstances, as an extremely peaceable neighbour, 

 which, from its want of water and atmosphere, is no longer 

 capable of any strong explosions." 



10. The hypothesis first suggested by Chladni is that which 

 appears to have met with most favour, having been adopted by 

 the most eminent astronomers of the present day to explain 

 these phenomena. It consists in supposing that, independently 

 of the great planets, there exist in the planetary regions 

 myriads of small bodies which circulate about the sun, 

 generally in zones, and that some of these zones intersect the 

 ecliptic, and are, consequently, encountered by the earth in its 

 annual revolution. The principal difficulties attending this 

 theory are the following : 



11. First, that bodies moving in groups in the circumstances 

 supposed, must necessarily move in the same direction, and con- 

 sequently they must become visible from one point and move 



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