462 Mr. R. P. Greg on Meteorolites or Aerolites, 



of air, aud frequently explode at great elevations. Their enor- 

 mous and probably planetary velocity, their oblique, nay, some- 

 times horizontal direction, frequently in a retrograde or opposite 

 direction to the earth's motion, are all perfectly subversive of the 

 idea of these meteoric masses having a terrestrial or atmospheric 

 origin. And there are other objections to M. Biot's and Prof. 

 Shepard's theory, such as the question, whence comes the large 

 quantity of nickel in meteoric irons ? It is an extremely rare 

 metal on the earth, and is only found in a few localities ; nor 

 does it, that I am aware of, constitute any portion of volcanic 

 matter hitherto analysed. 



It is not to be denied that there exist some phsenomena 

 of the meteoric class which have an atmospheric and therefore 

 terrestrial origin ; there are, we know, cases of electric action 

 producing certain kinds of fireballs ; there are falls of dust, black 

 rain, and even of viscid substances ; but it is necessary to sepa- 

 rate these cases from the regular meteoric masses, stone or iron, 

 and not indiscriminately attempt to account for all these things 

 by one theoiy, however ingenious, or howsoever in particular 

 cases and to a certain extent, correct. La Grange, Arago and 

 Humboldt all agree in rejecting the atmospheric origin of 

 aerolites. 



Having thus examined and rejected the theory of a terrestrial 

 origin of meteoric masses, I shall conclude by summing up the 

 principal points I have endeavoured to establish. 



First. That the deposition of meteoric matter on the surface 

 of the earth has not been, all things considered, otherwise than 

 uniform, ?. e. there is no decided tendency to local deposition. , 



Secondly. That their origin is not within the limits of the 

 earth's atmosphere. 



Thirdly. That they are probably distinct from ordinary lumi- 

 nous meteors, as regards both their physical nature and orbits, 

 and may also exhibit periodicity. (See Table F.) 



Fourthly. That their period of least common occurrence takes 

 place when the earth is on the side of the winter solstice in peri- 

 helion; while, on the other hand, the period of most frequent 

 occuiTcnce is when the earth is in aphelion, and the mean system 

 or mass of the asteroids in their perihelion. 



Fifthly. That they may reasonably be considered as belonging 

 to the group of planetoids or asteroids, and to partake, therefore, 

 of the proper nature and conditions of planetary bodies. 



Note I. p. 332. — One circumstance may be mentioned as being 

 rather singular, which is, the extraordinary number of meteoric irons, 

 discovered within a comparatively short period in the United States, 



