PHYSICAL DESCRIPTION OP THE UNIVERSE. 51 



which depend on the quantitative relations of matter or the 

 distribution of masses ; and which may therefore be contem- 

 plated as governed by simple dynamic laws. Effects due to 

 specific differences, or to heterogeneous qualities of matter, 

 do not as yet enter into our calculations of the celestial 

 mechanics. 



It is only through the phenomena of light (the propaga- 

 tion of luminous waves) and the effects of gravitation, that 

 the inhabitants of our earth enter into relation with matter 

 in space, whether existing in spheroids, or in a dispersed 

 form. The existence of a periodical influence of the sun or 

 moon on the variations of terrestrial magnetism is still highly 

 problematical. The only direct experimental knowledge which 

 we possess of any of the specific properties or qualities of 

 matter not belonging to our planet, is derived from the fall 

 of the aerolites or meteoric stones, already alluded to. 

 Their direction and enormous velocity of projection (a velo- 

 city wholly planetary) render it more than probable, that 

 these masses, enveloped in vapours and reaching the earth 

 in a state of high temperature, are small heavenly bodies, 

 which the attraction of our planet has caused to deviate 

 from their previous path. The aspect so familiar to us of these 

 asteroids, and the analogy which their composition presents 

 to the minerals of which the crust of our globe is formed, 

 are indeed very striking. The inference to which they point 

 appears to me to be, that the planetary and other masses 

 were agglomerated in rings of vapour, and afterwards in 

 spheroids, under the influence of a central body ; and that 

 being originally integral parts of the same system, they con- 

 sist of substances chemically identical. Pendulum experi- 

 ments, and especially those made by Bessel with so high a 



