296 MEMOIR ON METEORITES. 



last theory is understood by reading the views of Prof. C. U. 

 Shepard, as expressed in an interesting report on meteorites 

 published in 1848. The author* says: " The extra-terrestrial 

 origin of meteoric stones and iron masses seems likely to be 

 more and more called in question with the advance of knowl- 

 edge respecting such substances, and as additions continue to 

 be made to the connected sciences. Great electrical excitation 

 is known to accompany volcanic eruptions, which may reason- 

 ably be supposed to occasion some chemical changes in the 

 volcanic ashes ejected; these being wafted by the ascensional 

 force of the eruption into the regions of the magneto-polar 

 influence, may there undergo a species of magnetic analysis. 

 The most highly magnetic elements (iron, nickel, cobalt, chro- 

 mium, etc.), or compounds in which these predominate, would 

 thereby be separated, and become suspended in the form of me- 

 tallic dust, forming those columnar clouds so often illuminated 

 in auroral displays, and whose position conforms to the direc- 

 tion of the dipping-needle. While certain of the diamagnetic 

 elements, or combinations of them, on the other hand, may 

 under the control of the same force be collected into different 

 masses, taking up a position at right -angles to the former 

 (which Faraday has shown to be the fact in respect to such 

 bodies), and thus produce those more or less regular arches, 

 transverse to the magnetic meridian, that are often recognized 

 in the phenomena of the aurora borealis. Any great disturb- 

 ance of the forces maintaining these clouds of meteor-dust, 

 like that produced by a magnetic storm, might lead to the 

 precipitation of portions of the matter thus suspended. If 

 the disturbance was confined to the magnetic dust, iron masses 

 would fall ; if to the diamagnetic dust, a non-ferruginous stone. 

 If it should extend to both classes simultaneously, a blending 

 of the two characters would ensue in the precipitate, and a rain 

 of ordinary meteoric stones would take place. The occasional 

 raining of meteorites might therefore on such a theory be as 

 much expected as the ordinary deposition of moisture from 

 the atmosphere. The former would originate in a mechanical 



*I must, in justice to Prof. Shepard, say that since his paper was written 

 he has informed me that he no longer entertains these views ; and I would 

 now omit the criticism of them did they not exist in his memoir uncontra- 

 dicted, and also were they not views still entertained hy some. 



