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and differing in magnitude and figure, compose the bodies called compounds.

“The hypothesis is framed to accord with experiments which are thought to indicate the conversion of any one of our elements into another, and answers no end except that of enabling us to acquiefce in our ignorance of the processes of Nature : For, according to the hypothefis, nothing more is requisite towards such a converfion, that a process wherein the ultimate parts of a body may be made to assume new arıangements and to form larger or smaller particles."

We readily agree, with Dr. H. that this hypothesis is extremely deficient, if it infers nothing more requisite to the formation of chemical elements, than a mere mechanical process, the simple effect of accumulating attractions. For, though we do not conceive the general attraction of matter to be a quality inherent in the primary atoms; but the mechanical effect of their reciprocal existence and action, we can by no means impute the chemical molecules or elements to a fortuitous combination of such atoms: and yet fortuitous it seemingly must be if those elements are mutable and interchangeable, unless we suppose the Creator constantly attentive to supply their waste, and keep up their number. Admitting, with philosophers, that the phænomena of nature are regularly produced, according to an established method and order; the chemical elements, as well as the germs of plants and animals must have an immutable, or at least a very permanent, existence. They must be regarded as organical molecules, whose properties are permanent and iminutable.

As these, however, are not the primary physical atoms, of which they are compounded, those permanent properties do not depend on the identical atoms of which they are composed. Like other compound bodies, they may exist and preserve their own identity, during the constant admission and disiniffion of their constituent atoms; and therefore it is necessary that such compound elements, however different from each other, should be formed of hetero-eneous atoms.

The mistake seems to lie in supposing elementary and other compounds to be the mere result of apposition and accretion of limple matter ; whereas they are the contrived combination of complicated motions. The two simplest and most general principles in nature are polver and direction ; the properties of all b dies whatever being the mechanical effect of thele; resulting from their original disposition by the Creator. Thus the action of every body in nature is mechanical, and its force a mere mmechanical force; the direction of such force, or the combination of the inechanic powers, however, constituting

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fuchi

fuch bodies, must be the effect of design, immediately resulting from a first cause, and constituting those properties in such elements as our author calls eletrive.-There requires nothing more, therefore, to settle the difference between us and our author than that he make a distinction between chemical elements and physical ones; not recurring to particular expedients to solve general phænomena, because they are necessary to solve particular ones.

We shall readily give up to him the expediency of having recourse to permanent immutable elements, in order to account for the particular phænomena of the mineral, vegetable and animal kingdoms. We readily admit, that the organical moleculæ, which contribute to the composition of bodies in each, are more than mere accumulations or coinbinations of inert:

matter.

They poffefs poperties, arising from a contrived and permanent fyftein of motion, or a combination of powers conftantly and consistently exerted in particular dir: clions. The peculiar properties hence arising, however, by no means exempt them from, although in fo:ne cates they may counteract, the more general principles of physical action.-Having premited this, we shall quote what Dr. Higgins obleries on the immutability of the primary elements of matter.

" I know not any doctrine so injurious to the cau e of natural philofophy, as that, of the conversion of bodies ; for it diveris men from the examination of what really happens to bodies in many interesting operations; and it stops all enquiry into the properties of the ultimate parts of matter; which enquiry is the mult important of all that can eagage a modern philofopher.

" As it is my purpose rather to explain and recommend; than to eiforce thele notions concerning the parts and properries of matter, I omit a great number of ob ervations, which might be offered in confirmation of them; and preiuming that iny readers will collect, from the following sections, several arguments tú the effict, I shall conclusie this part with the following remarks.

“ As nothing less than a fupernatural agent can annihilate matter that is once created, so nothing less can make the pirts ut uir to attract each other as the parts of earth or of water do; or can withdraw from any parts of matter the properties or powers once atligned to them; or can caute the heterogeneal paris to exchange their properties : and as all the parts of the known fyítem appear, to tar as we can discern, to be governed by inceffant and immutable laws, and to be tramed with lo in uch prescience and wildom that they require no new alterations, regulations, or tubititutions, of them ; we ought to conduct our en. quiries concerning natural bodies, by this rule; that the figure, or fize, or property, of an atom at any one time, is the tigure and size, and property of the fame at all times ; and that the powers which

cause

cause the relations of matter, act incessantly; and that most of the va. rieties observable in bodies, depend on the composition and counter. action of these powers, during the combination of diffimilar parts of matter."

The attentive reader will see, that if our author had confined his immutability of elements to those of the intermediate or secondary kind, such as the elementary inoleculæ or constitucnt parts of natural bodies, instead of extending it to the ultimate parts of matter in general, we thould have had no objection to this part of his argument. - As it is, we should, totis viribus, oppose his attempt to establish attraction as a primary property in the elements of matter, did we not conceive his assumption 100 precipitate, and his arguments too confused to promise it any success.-We shall pass over, therefore, his ineffectual reprehensions of Sir Isaac Newion on this head, and his insufficient endeavours to prove him inistaken in matters; wherein his fagacity, like that of Lord Bacon, prophetically pointed out what innumerable experiinents have since served to confirm. Among these is, the existence of an universal elastic medium, or ether; the reality of which, because he has no use for it, Dr. Higgins denies. But, to take leave of our author's introduation, and come at length to his Observations on Light; the profeffed subject of his Essay.-And here again, we cannot help conceiving he makes a false ft p at the threshold. It is indeed, the misfortune of most of our cheirical theorists, that they are deficient in the principles of the mechanical philosophy. Hence it is that they lo often mistake fubftance for power, matter for motion, and vice versa. At the same time, also, they are apt to be too negligent of logical distinctions and precision of terms. Thus our author sets out, in his first chapter, to prove that “ a motion of light is necessary towards illumination and vision.” He might almost as well have faid the motion of light is necessary to its existence; in which he would have not been far from the truth, as light is in fact only a species of motion.

“ In a roum encompassed by opaque walls and floors, we have no visual sense of cbjects nor of light; and we find that this darkness is either privation or quiescence of light. When a body in the act of combustion is brouybt into the room, we have visual senle of light and of the objects in the room; and hence we learn, that not only the presence of light, but a motion of light, is neceffary towards illumination and vision. For, if we suppose the light to be emitted from the burning body, the velocity with which it ipreads excentrically to every part of the room, from the burning body, denores a rapid motion of the light: but when we admit that no light is projected from the burning body, then must we conclude, that the matter of light existed

previously

Previoufly in every mensurable part of the room, and during the utter darkness of it; and that fince the quiefcence of Light is darkness, the motion of light is the cause of illumination, and we can see objects only by light in motion."

What a pity, that our chemical philosopher was obliged to bring a body into the room, in the act of combustion, in order to let his light in motion! A North American savage might with two sticks of wood, or a country blackfinithi with two pieces of cold iron, have foon made motion enough to produce illumination and vision, without the aid of culinary fire.

Such mere mechanical light-makers, however, might not have philosophy enough to know that, they could not see in the presence of light, without first putting it in motion. They might te fuch simpletons as to suppose the light absent, when they were in ud ter darkness, and infolently arrogate to themfelves the power of making light! But we here learn from our Jearned do&or, that, whether we fuppose the light projected from the luminous body or not, it was present, and lay quietly in the dark, till their stirring about put it into motion. We cannot help remarking, on this occasion, the extreme absurdity, ihany of our philosophers are guilty of, in their abuse of words, in treating of light, fire, &c. A Mr. Jones of Oxford, author of an Essay on the Principles of Natural Philosophy, published fome year's fince, thus uses fire, light, and ather, as of one and the fame meaning. “ We must not imagine, said that reverend physiologist, that heat and cold are diferent in their nature ; it being the very fame element, fire, that both boils Water and freezes it." In like manner our author tells us, in fact, that light both illuminates and envelopes us in darkness, juft as it is active or quiescent. Hear how he makes it out.

“ When the pyrophorus of Komberg is fecluded from the immediate action of air, and is brought into the chamber; neither this pyropho. sus nor any other ohjat is visible; but when the pyroplorus expofed to air, enters into coumbustion, it is visible, and illuminates other objects. And since th: illumination continues whilst phlogistic maiter is emitted from the pyrophorus, and ceases when this emillion ceases, and when the reliduary matter of the pyrophorus is dephlogisticated or incombustible; it is evident that, it the light feen, be projected from the substance of the pyrophorus, it is seen only during the ra. pid motion of it, and if the light was not emitted from the pyrophorus, the illumination is owing to a motion which the circumambient light receives from the phlogutic matter which is certainly emitted irom the pyrophorus.

The phosphorus of Kunkel causes no illumination, whilst it is kept in the Torricellian void, and whilst it is by any means prevented • Vol. VI.

from

from emitting its phlogiston. The same phosphorus illuminates, more or leis, as the quantity of phlogiston which elcapes from it, in a given time, is greater or less; and the illumination ceases when the pblogiston is departed from the residuary incombustible faline matter, which with the fresh phloģiston of any phlogistic body is capable of forming phora phorus again. And since the phosphorus is luminous only whilft matter is manifefly moved from it; we clearly perceive that light at rest, whether in the phosphorus or diffused in the chamber, is not sensible to us; and that the illumination caused by phosphorus conlists in the motion of light emitted from the phosphorus, or in the motion which diffused and quiescent light receives from the inoved phlogiston of the phosphorus."

Well, reader, what say you to the pyrophorus of Komberg, the phosporus of Kunkel, and the phlogiston of Higgins ? Do not the pyrophorus and the phosphorus, and the phlagiston illuminate your understanding, and make our author's light as clear as the sun at noon-day?-No! Attend then to a short arguinent, a little more obvious and mechanical. Light, properly fo called, is never either quiescent or utterly dark. Where utter darkness prevails, Light is not present, but totally absent. Light is a motion propagated, in vibrations, through that subtle elastic medium, which is intimately mixed with the grosser atmosphere, and is extended through the whole region of space ; agreeable to the opinions of the best modern philosophers *. Şir Isaac Newton, it is true, for reasons favourable to his mathematical mode of treating the subject, chose to consider light as a body projected from the luminous obje&. This opinion has been, of course, adopted by almost all the mathematical writers on the subject ; others have, with more reason, rejected it; among which is Dr. Higgins; who refutes not feebly the opinion of Sir Isaac on such supposed projection.

“ The fluids + which escape from bodies during the combustion or decomposition of them, expand eccentrically from the bodies, by the repulfive powers of their parts. If light be coinbined in bodies, we know no other cause of its emanation from them during their combination, except repulfive powers of its parts, funilar to the foregoing repulsive powers ; and light flowing from bodies by such powers, and with such forces, would impel and move the bodies opposed in its course, and especially those bodies which reflect light or are said to stop

* Viz. Huygens, before Sir I. N. and Le Cat, Euler, and others since.

+ The doctor should have said efluvia; a finid being rather an unitedly gravitating bods, in the atınosphere of some other ligbler fluid; whereas the effirevia, projected from bodies during combustion, or any other decompofition, are separately floating solids in a fluid generally heavier than themfelves. Rev.

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