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 unphilosophical 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 composition, and those attractions that are not determined solely by the relations of mass, we must admit that the description of the earth comprises at p 63 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,* 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. [footnote] * On the question already discussed by Newton, regarding the difference 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 'Mecanique Celeste', p. 3, 4; Kant, 'Metaph. Anfangegrunde der Naturwissenschaft, Säm. Werke', 1839, bd. v., s. 309 (Metaphysical Principles of the Natural Sciences); Pectet, 'Physique', 1838, vol. i., p. 59-63. 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 depending upon the quantitative relations of matter of 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.