44 COSMOS. 



other species of the same family ; and that this law of sub- 

 stitution, which seems to depend upon some inherent mys- 

 teries of the organism, considered with reference to its origin, 

 maintains in contiguous regions a numerical relation between 

 the species of various great families and the general mass of 

 the phanerogamic plants constituting the two floras. We 

 thus find a principle of unity and a primitive plan of dis- 

 tribution revealed in the multiplicity of the distinct organiza- 

 tions by which these regions are occupied ; and we also 

 discover in each zone, and diversified according to the families 

 of plants, a slow but continuous action on the aerial ocean, 

 depending upon the influence of light the primary condition 

 of all organic vitality on the solid and liquid surface of our 

 planet. It might be said, in accordance with a beautiful 

 expression of Lavoisier, that the ancient marvel of the myth 

 of Prometheus was incessantly renewed before our eyes. 



If we extend the course which we have proposed, following 

 in the exposition of the physical description of the earth to 

 the sidereal part of the science of the Cosmos, the delineation 

 of the regions of space and the bodies by which they are 

 occupied, we shall find our task simplified in no common 

 degree. If, according to ancient but unphiiosophical forms of 

 nomenclature, we would distinguish between physics, that is 

 to say, general considerations on the essence of matter, and 

 the forces by which it is actuated, and chemistry, which 

 treats of the nature of substances, their elementary com- 

 position, and those attractions that are not determined solely 

 by the relations of mass, we must admit that the description 

 of the earth comprises at once physical and chemical actions. 

 In addition to gravitation, 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 affinity, act upon molecules in 

 contact, or at infinitely minute distances from one another,* 



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

 ence existing between the attraction of masses and molecular attraction, 

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

 to book x. of the Mecamquc Celeste, pp. 3, 4 ; Kant, Metaph. Anfangs- 

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

 physical Principles of the Natural Sciences); Pectet, Physique, 1938, 

 vol. i., pp. 59 63. 



