INTRODUCTION. 46 



and which being differently modified by electricity, heat, 

 condensation in porous bodies, or by the contact of an 

 intermediate substance, animate equally the inorganic world 

 and animal and vegetable tissues. If we except the small 

 asteroids which appear to us under the forms of aerolites 

 and shooting stars, the regions of space have hitherto pre- 

 sented to our direct observation physical phenomena alone ; 

 and in the case of these, we know only with certainty the 

 effects depending upon the quantitative relations of matter or 

 the distribution of masses. The phenomena of the regions of 

 space may consequently be considered as influenced by simple 

 dynamical laws the laws of motion. 



The effects that may arise from the specific difference and 

 the heterogeneous nature of matter, have not hitherto entered 

 into our calculations of the mechanism of the heavens. The 

 only means by which the inhabitants of our planet can enter 

 into relation with the matter contained within the regions of 

 space, whether existing in scattered forms or united into 

 large spheroids, is by the phenomena of light, the propagation 

 of luminous waves, and by the influence universally exercised 

 by the force of gravitation or the attraction of masses. The 

 existence of a periodical action of the sun and moon on the 

 variations of terrestrial magnetism is even at the present day 

 extremely problematical. We have no direct experimental 

 knowledge regarding the properties and specific qualities of 

 the masses circulating in space, or of the matter of which 

 they are probably composed, if we except what may be derived 

 from the fall of aerolites or meteoric stones, which, as we 

 have already observed, enter within the limits of our ter- 

 restrial sphere. It will be sufficient here to remark, that the 

 direction and the excessive velocity of projection (a velocity 

 wholly planetary) manifested by these masses, render it more 

 than probable that they are small celestial bodies, which being 

 attracted by our planet are made to deviate from their original 

 course, and thus reach the earth enveloped in vapours, and in 

 a high state of actual incandescence. The familiar aspect of 

 these asteroids, and the analogies which they present with 

 the minerals composing the earth's crust, undoubtedly afford 

 ample grounds for surprise ;* but, in my opinion, the only con- 



* [The analysis of an aerolite which fell a few years since in Maryland, 

 United States, and was examined by Professor Silliman of Newhaveu, 



