2. Now we have to observe concerning this agent, Friction, that we have no ground for asserting it to be a necessary result of other properties of matter, for instance, of their solidity and coherency. Philosophers have not been able to deduce the laws of friction from the other known properties of matter, nor even to explain what we know experimentally of such laws, (which is not much,) without introducing new hypotheses concerning the surfaces of bodies, &c.--hypotheses which are not supplied us by any other set of phenomena. So far as our knowledge goes, friction is a separate property, and may be conceived to have been bestowed upon matter for particular purposes. How well it answers the purpose of fitting matter for the uses of the daily life of man, we have already seen. We may make suppositions as to the mode in which friction is connected with the texture of bodies; but little can be gained for philosophy, or for speculation of any kind, by such conjectures respecting unknown connexions. If, on the other hand, we consider this property of friction, and find that it prevails there, and there only, where the general functions, analogies, and relations of the universe require it, we shall probably receive a strong impression that it was introduced into the system of the world _for a purpose_. 3. It is very remarkable that this force, which is thus so efficacious and discharges such important offices in all earthly mechanism, disappears altogether when we turn to the mechanism of the heavens. All motions on the earth soon stop;--a machine which imitates the movements of the stars cannot go long without winding up: but the stars themselves have gone on in their courses for ages, with no diminution of their motions, and offer no obvious prospect of any change. This is so palpable a fact, that the first attempts of men to systematize their mechanical notions were founded upon it. The ancients held that motions were to be distinguished into _natural_ motions and _violent_,--the former go on without diminution--the latter are soon extinguished;--the motions of the stars are of the former kind;--those of a stone thrown, and in short all terrestrial motions, of the latter. Modern philosophers maintain that the laws of motion are the same for celestial and terrestrial bodies;--that all motions are _natural_ according to the above description;--but that in terrestrial motions, friction comes in and alters their character,--destroys them so speedily that they appear to have existed only during an effort. And that this is the case will not now be contested. Is it not then somewhat remarkable that the same laws which produce a state of permanent motion in the heavens, should, on the earth, give rise to a condition in which rest is the rule and motion the exception? The air, the waters, and the lighter portions of matter are, no doubt, in a state of perpetual motion; over these friction