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similar parts, less and less, without end, as water into vapour, more or less, subtile and attenuated. Aristotle and his followers esteemed earth, air, fire, and water, to be elements, simple and uniform in their several kinds, essentially distinct and utterly incapable of being converted into one another, yet easily uniting together, and by their different arrangements, and properties and mixtures, composing every body in the universe. Many modern chemists have adopted this idea ; others have increased the number of elements, by adding a saline principle; others have contended that some of these elements, air and fire for instance, are themselves compound bodies; and others, lastly, are persuaded, that there is only one elementary homogeneal principle, and that all the varieties of bodies, as well as of what are most commonly esteemed elements, ought to be attributed to the different magnitudes and figures of the particles composing them; and as the component parts of water or air, or any other body, are by no means supposed to be elementary particles of matter, but to be made up of different numbers of elementary particles, arranged in different forms, it may be thought probable, that mechanical causes may either diminish or augment the number, or change the disposition of the particles, and thus effect the several varieties observable in nature.

“ It would be improper in this place to enlarge on a subject, concerning which both ancient and modern philosophers have been so much divided in opinion. Their great diversity of sentiment may suggest a suspicion that the full comprehension of it does not fall within the reach of the human understanding. The following observation may, perhaps, tend a little to illustrate this matter. Let us suppose that this terraqueous globe was not surrounded with any air or atmosphere, and that by an approach to the sun, or an increase of subterranean fires, by some means or other it should become exposed to a heat four times greater than the medium heat of summer, which we may reckon to be about 60 degrees of Fahrenheit's thermometer; then would an atmosphere be quickly formed around it, all the water on its surface, most of the juices of plants and animals, and a great variety of mineral particles, would be raised up in vapours and exhalations, and whilst the heat continued would be kept suspended in an elastic state, and constitute an atmosphere analogous, as it may reasonably be imagined, to the chaotic state of our present atmosphere, only differing from it in this, that it would require a greater degree of heat in order to keep the particles of matter from coalescing into one heterogeneous mass. Again, in the present state of the atmosphere, suppose that a great degree of cold should continue unabated for any length of time, all the water on the surface of the earth would be changed into a solid transparent stone, which might be dug out of its quarry, and then employed in building as well as marble, or any other species of stone ; all the particles of air would be bronght closer together; some of them which were the least elastic would be reunited: and imagining the cold to be indefinitely increased, what reason can there be against supposing that the whole atmosphere would be reduced into a solid state, forming a heterogeneous crust on the surface of the earth; the thickness of this crust, supposing it to be as dense as marble, would be about four yards? It will easily be understood, that water, and air, and earth are, upon this hypothesis, but variations of the same element introduced by heat.

“That the atmosphere which surrounds the earth was originally formed from the chaotic mass, by having the more subtile parts of which that mass consisted, elevated and put into an elastic state by means of heat, seems not altogether improbable. We find the atmosphere or firmament immediately succeeding the formation of light; now, if the effect of that light was heat, be the form or matter of it what you please, then would such particles of the shapeless jumble as were capable of being evaporated with that degree of heat, be elevated in an elastic state, and a division or separation would be made in the midst of the great abyss, between the waters which were of a nature subtle enough to be converted by that degree of heat into an elastic fluid, constituting the firmament or atmosphere, and the waters which could not be evaporated in that degree of heat, but still remained covering the surface of the globe, being not collected into one place, that the dry land might appear, till the third day. This notion of the atmosphere and its formation, seems to be conformable enough to Newton's opinion expressed in his letter to Mr. Boyle. “I conceive the confused mass of vapours, air, and exhalations, which we call the atmosphere, to be nothing else but the particles of all sorts of bodies of which the earth consists, separated from one another and kept at a distance by the said principle," a principle of repulsion.”*

Here we have the one element again or matter treated simply as matter generally, in the same way in which metaphysicians have dealt with it, leaving heat and, probably as by others expressed, some general plastic power to form all the modifications. This is much too indefinite for science, and it is surprising that it should have been deemed sufficient even in Bishop Watson's time. There is no attempt to examine the degree of heat which may convert a solid body into a permanent gaseous one, and no difficulty perceived in the persistence of the atmosphere in a gaseous state whilst exposed to no more cold than the solid or liquid substances around us, or the persistence of the water in a liquid state, or the permanency of the earth, why it did not occasionally send off rocks into vapour or rarefy them into air ; nor is there any attempt to find what strange powers may cause the diversity of structure. Although not expressed, these words were evidently

* Chemical Essays. By R. Watson, D.D., F.R.S., &c. Vol. I., p. 100. 4th Edition. London, 1787.

seen.

written under the idea that the powers of nature worked rather arbitrarily and capriciously; how, is not distinctly

When the mixture of pure elements is spoken of as forming all bodies, there is a reason given clear enough for the changes, and the chief blame attached to those who believed in this is, that they did not obtain the amount of each needed to form any one distinct substance. This proves, as it appears to me, that they held their opinions by a very slender tie.

Boscovich, in his theory of natural philosophy, in 1759, gave the fullest scientific expression of the unsubstantial theory of matter, which may be called the dynamical. The book is not common, and not to be found in this neighbourhood. I shall take Dr. Daubeny's description : “He supposes that matter is made up of a number of unextended indivisible points, which, however, never touch each other, owing to the mutual repulsion subsisting between them, so soon as they come within a certain distance of each other; which repulsion increasing gradually in proportion as they are made to approach nearer and nearer, becomes at length too powerful for any

force to overcome. In this theory we have again revived in another form the idea that all matter comes from a non-material, or what we may call a spiritual force, nor is it easy for us to conceive how it could have any other origin. It is a revival of the doctrine of the mind and of the soul being the origin of matter, or of the early opinion that numbers were the true beginning, or in other words, abstract forces. But we have to do with matter when it is formed, not with its production; and when these unextended points have obtained existence, we are obliged to reason on them as if real. One result, however, affects our subject, that by this theory, matter may cease to be infinitely divisible. It does not of necessity cease to be so, as we may readily believe, in the constancy of these points; but we may also imagine the power dispersing in various directions, and the absolute amount of force existing in one particle to lie diffused throughout the whole world, or any given amount

* An Introduction to the Atomic Theory. By Charles Daubeny, M.D., F.R.S., &c. Second edition, Oxford, 1850. p. 34.

of space.

When the particles are formed, Boscovich deals with them exactly as with matter, formed of indestructible atoms. “ Thus he supposes that the points of matter alternately attract and repel each other, according to the distance that separates them, until they either come very close to, or are removed to a comparatively great distance from each other; in the former case they are repelled, in the latter attracted; the former force preventing mutual contact, the latter, which, when considered as acting between the earth and bodies upon it, is no other than gravitation, drawing them all together."

The Encyclopedie Methodique,* in an article written by G. Morveau, 1786, may be presumed to give the advanced opinion of chemists. He says,

“ Are there really different degrees of saturation of the same salt ? or is not the union which it contracts with that portion which exceeds the point of saturation, the effect of supercomposition, as in combination with a third foreign body ? This is a question which merits all our attention, not only because it is of interest in the general theory of chemical attraction, but rather because it is of importance that we should understand what is the character of the affinity before we attempt to submit it to calculation, or even deduce a satisfactory explanation of the phenomena which depend on it. I confess that the idea of divers degrees of saturation of one body with another appears to me repugnant to all the notions

• Vol. I., p. 560-1. Encyclopedie Methodique. Chymie Pharmacie et Metallurgie. Paris, 1786-1815.

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