INTRODUCTION. (53 



once physical and chejiiical actions. In addition to gravita- 

 tion, which must be considered as a primitive force in nature, 

 we observe that attractions of another kind are at work around 

 us, both in the interior of our planet and on its surface. These 

 forces, to which we apply the term chemical ajjinity, act upon 

 molecules in contact, or at infinitely minute distances from one 

 another,* 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 presented to 

 our direct observation physical phenomena alone ; and in the 

 case of these, we know only with certainty the effects depend- 

 ing upon the quantitative relations of matter or the distribu- 

 tion 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 heteroofeneous 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 ex- 

 istence of a periodical action of the sun and moon on the va- 

 riations of terrestrial magnetism is even at the present day 

 extremely problematical. We have no direct experimental 

 knowdedge regarding the properties and specific qualities of 

 the masses circulating in space, or of the matter of w^hich they 

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

 the fall of aerolites or meteoric stones, wdiich, as we have al- 

 ready observed, enter within the limits of our terrestrial 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 



* On the question already discussed by Newton, regarding the differ- 

 ence existing between the atti-action of masses and molecular attraction, 

 see Laplace, Exposition du Systeme du Monde, p. 384, and supplement 

 to book X. of the Mecanique Celeste, p, 3, 4 ; Kant, Metaph. AnfangR. 

 grunde der Naturwissenschaft, Sam. Werke, 1839, bd. v., s. 309 (Meta- 

 physical Principles of the Natural Sciences) ; Pectet, Physique, 1838- 

 vol, i., p. 59-63. 



