He tells us himself, that he was led to the study of general physics, from those views of the properties of body which had occurred to him in the prosecution of his chemical and mineralogical inquiries. In those speculations, therefore, that extended so far into the regions of abstract science, he began from chemistry; and it was from thence that he took his departure in his circumnavigation both of the material and intellectual world.

The chemist, indeed, is flattered more than any one else with the hopes of discovering in what the essence of matter consists; and Nature, while she keeps the astronomer and the mechanician at a great distance, seems to admit him to more familiar converse, and to a more intimate acquaintance with her secrets. The vast power which he has acquired over matter, the astonishing transformations which he effects, his success in analyzing almost all bodies, and in reproducing so many, seem to promise that he shall one day discover the essence of a substance which he has so thoroughly subdued; that he shall be able to bind Proteus in his cave, and finally extort from him the secret of his birth; in a word, that he shall find out what matter is, of what elements it is composed, and what are the properties essential to its existence.

In entering upon this new inquiry, Dr Hutton was forcibly struck with the very just reflection, That we do by no means explain the nature of

body, when we describe it as made up of small particles; because, if we allow to these particles any magnitude whatsoever, we do no more than affirm that great bodies are made up of small ones. The elements of body must, therefore, be admitted to be something unextended. To these unextended elements Dr Hutton gave the name of Matter, and carefully distinguished between that term and the term Body, which he applied only to those combinations of matter that are necessarily conceived to possess impenetrability, extension, and inertia.

The most accurate examination of the properties of body confirms the truth of the opinion, that it is composed of unextended elements. Bodies may be compressed into smaller dimensions; many by the application of mechanical force, and all by the diminution of their heat: nor is there any limit to this compression, or any point beyond which the farther reduction of volume becomes impossible. This holds of substances the most compact, as well as the most volatile and elastic, and clearly evinces that the elements of body are not in contact with one another, and that in reality we perceive nothing in body but the existence of certain powers or forces, acting with various intensities, and in various directions. Thus the supposed impenetrability, and of course the extension of body, is nothing else than the effort of a resisting or repulsive power; its cohesion, weight, &c. the efforts of

attractive power; other properties.

and so with respect to all its

But if this be granted, and if it be true that in the material world every phenomenon can be explained by the existence of power, the supposition of extended particles as a substratum or residence for such power, is a mere hypothesis, without any countenance from the matter of fact. For if these solid particles are never in contact with one another, what part can they have in the production of natuappearances, or in what sense can they be called the residence of a force which never acts at the point where they are present? Such particles, therefore, ought to be entirely discarded from any theory that proposes to explain the phenomena of the material world.

ral

Thus, it appears, that power is the essence of matter, and that none of our perceptions warrant us in considering even body as involving any thing more than force, subjected to various laws and modifications.

Its

Matter, taken in this sense, is to be considered as indefinitely extended, and without inertia. presence through all space is proved by the universality of gravitation; and its want of inertia, by the want of resistance to the planetary motions. Thus, in our inquiry concerning physical causes, we are relieved from one great difficulty, that of supposing matter to act where it is not. The force of gravi

tation, according to this system, is not the action of two distant bodies upon one another, but it is the action of certain powers, diffused through all space, which may be transmitted to any distance. There seems to me, however, to remain a difficulty hardly less than that from which we appear to be relieved, viz. to assign a reason why the intensity with which such powers act on any body, should depend on the position and magnitude of all the bodies in the universe, and should bear to these continually the same relation. But, however this be, the ingenuity of Dr Hutton's reasonings cannot be questioned, nor, I think, the justness of many of his conclusions. His explanations of cohesion, heat, fluidity, deserve particular attention. In one thing, however, he seems to have fallen into an error, which runs through much of his reasoning, concerning the principles of gravitation and inertia. He affirms, that "without gravity, a body endowed with all the other material qualities would have no inertia ; that it would not diminish the velocity of the moving body by which it should be actuated, nor would it move a heavy body whatever were its velocity."* Now, this proposition, though from its nature it cannot be brought to the immediate test of experience, is certainly inconsistent with the principles of mechanics; at the same time, it is true, that we would

Dissertations, &c. p. 312, § 31.

not, in the case here supposed, have the same means of measuring the motion lost, or gained by collision, which we have in the actual state of bodies. This is perhaps what misled Dr Hutton; and though his remarks on the measures of motion and force are very acute, and many of them very just, the mathematical reader will regret the want of that mode of reasoning, which has raised mechanics to so high a rank among the sciences.

It is impossible not to remark the affinity of this theory with that of the celebrated Boscovich, in which, as in this, all the phenomena of the material world are explained, by the supposition of forces variously modified, and without the assistance of solid or extended particles. These forces are supposed to be arranged round mathematical points, which are moveable, and act on one another by means of the forces surrounding them. A most ingenious application of this principle is made to all the usual researches of the mechanical philosophy, and, it must be confessed, that few theories have more beauty and simplicity to recommend them, or do better assist the imagination in the explanation of natural appearances. But it involves, in the whole of it, this great difficulty, that mathematical points are not only capable of motion, but capable of being endowed, or, at least, distinguished, by physical qualities. Dr Hutton, in his theory, has avoided this difficulty, by giving no other than a