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



meteoric irons and stones ; a theory principally supported by the 

 chemists and electricians, as Sir H. Davy, Fusinieri, M. Biot, 

 Prof. Shepard, M. F. G. Fischer and others. Before concluding 

 this paper I shall shortly allude to this theory, as it bears 

 strongly on the general subject. I cannot do better than again 

 quote from Prof. Shepard. (See his Report on American Me- 

 teorites, published in the American Journal of Science.) 



"The extra-terrestrial origin of meteoric stones and iron 

 masses seems likely to be more and more called in question, with 

 the advance of knowledge respecting such substances, and as 

 additions continue to be made to the connected sciences ; I may 

 therefore take an early occasion of presenting some views, 

 founded partly upon Biotas theory of the aurora borealis, which 

 seem to favour such an origin of meteorites. 



" The recent study of those frequently occurring and wide- 

 spread atmospheric accumulations of meteoric dust (a single case 

 being recorded where the area must have been thousands of 

 square miles in extent, and where the quantity of earthy matter 

 precipitated must have been from 50 to 500,000 tons in weight), 

 makes known to us the vast scale on which terrestrial matter is 

 often pervading the regions of the upper atmosphere, and pre- 

 pares us to appreciate the mode in which peculiar constituents 

 of meteorites may be translated to those remote distances, where, 

 according to the theory of Biot, the clouds of meteoric dust are 

 retained. 



" Great electrical excitation is known to accompany volcanic 

 eruptions, which may reasonably 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, chromium, &c.), or compounds in which these 

 predominate, would thereby be separated and become suspended 

 in the form of metallic dust, forming those columnar clouds so 

 often illuminated in auroral displays, and whose position con- 

 forms to the direction 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 re- 

 cognized in the phaenomena of the aurora borealis. 



" Any great disturbance 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. 



