METEOKIC STONES AND SHOOTING STARS. 



the Parian Marbles," and which fell about the year of the birth 

 of Socrates, has been described as being of the size of two 

 mill-stones, and equal in weight to a full waggon load. In the 

 beginning of the tenth century an enormous meteoric mass fell 

 into the river near Narni, the magnitude of which was so great, 

 that when resting on the bottom, it projected four feet above the 

 surface. 



According to a popular tradition in Mongol, there is, in a 

 plain near the sources of the Yellow River in Western China, a 

 fragment of black rock forty feet high, which fell from heaven. 



It is observed by Humboldt, that great as these masses are 

 they can only be regarded as fragments of the mass which 

 exploded in the fire-ball, or was hurled from the cloud. 



The heights at which these objects have been visible, and the 

 actual velocities of their motion, will be presently noticed. 



7. Such are the circumstances attending the exhibition of these 

 meteors, which have been collected from careful and accurate 

 information. Let us now turn our attention to the different 

 methods by which it has been attempted to explain them. 

 Four different hypotheses, or theories, have been proposed for 

 this purpose. 



First. It is supposed that the matter composing them has 

 been drawn up from the surface of the earth in a state of 

 infinitely minute subdivision, as vapour is drawn from liquids ; 

 that, being collected in clouds in the higher regions of the 

 atmosphere, it is there agglomerated and consolidated in masses, 

 and falls by its gravity to the surface of the earth ; being occa- 

 sionally drawn from the vertical direction which would be 

 imparted to it by gravity, by the effect of atmospheric currents 

 and thus occasionally striking the earth obliquely. We shall 

 call this the atmospheric hypothesis. 



Secondly. It is supposed that meteoric stones are ejected from 

 volcanoes, with sufficient force to carry them to great elevations 

 in the atmosphere, in falling from which they acquire the 

 velocity and force with which they strike the earth. The 

 oblique direction with which they strike the ground is explained 

 by the supposition that they may be projected from the volcanoes 

 at corresponding obliquities, and that, by the principles of pro- 

 jectiles, they must strike the earth at nearly the same inclination 

 as that with which they have been ejected. This we shall call 

 the volcanic hypothesis. 



Thirdly. It has been suggested that meteorites may be bodies 



which have been ejected from lunar volcanoes, with such a force 



that they may have departed from the moon to a distance so 



great, as to come within such a distance of the earth, that the 



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