72S lECTORE LVII. 



in its orbit. The rapidity of their motion, as well as its occasional deviation 

 from a right line, has generally been considered as a reason for supposing 

 that they depend on electricity; but the opinion is by no means fully esta- 

 blished. 



Other igneous meteors, which nearly resemble in their appearance the 

 largest of these, are sometimes observed to fall on the earth, either entire or 

 divided : and after their fall, certain stones have been found, which have 

 been supposed to have descended in an ignited state. Mr. Howard has ascer- 

 tained that almost all these stones agree in their general characters, and in 

 their chemical analysis, especially in the circumstance of containing nickel. 

 It has been conjectured, both in this country and on the continent, that they 

 have been emitted by lunar volcanos, and it has been observed, that since they 

 would find little or no resistance from the very rare atmosphere of the moon, 

 they would require a velocity of projection only four times as great as that 

 which a cannon ball sometimes receives, in order to rise into the sphere of 

 the earth's attraction. Their heat and combustion may not improbably be 

 derived from the great condensation which they must occasion in the air im- 

 mediately before them, and even their friction might easily produce enough 

 of electric light, to render them visible in the dark. Among many such sub- 

 stances projected from the moon, it is probable that a few only would be di- 

 rected towards the earth, and many more would be made to revolve in ellipses 

 round it, and become little satellites, too small for human observation, ex- 

 cept when they enter far enough into the atmosphere to produce an appear- 

 ance of light, resembling that of a shooting star ; but it is scarcely probable 

 that their velocity could ever be at all comparable with that which has been 

 attributed to these meteors. There is, however, no difficulty in supposing, on 

 the other hand, that the wandering substances, which may be moving through 

 empty space, with a velocity equal to that of the shooting stars, may be so 

 much retarded, when they penetrate deep into our atmosphere, as to make 

 but a moderate impression by their fall on the ground; and if we suppose 

 the meteors to be of one kind only, they must be referred rather to the de- 

 scription of shooting stars than to that of the productions of lunar volcanos; 

 although the undulatory motion, sometimes observed in these meteors seems to 

 be in some measure inconsistent with the progress of a heavy body, moving by 

 means of its natural inertia in a straight line. 



