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

"The hypothefis is framed to accord with experiments which are thought to indicate the converfion of any one of our elements into another, and anfwers no end except that of enabling us to acquiefce in our ignorance of the proceffes of Nature: For, according to the hypothefis, nothing more is requifite towards fuch a converfion, that a procefs wherein the ultimate parts of a body may be made to affume new arrangements and to form larger or fmaller particles."

We readily agree, with Dr. H. that this hypothefis is extremely deficient, if it infers nothing more requifite to the formation of chemical elements, than a mere mechanical procefs, the fimple 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 exiftence and action, we can by no means impute the chemical molecules or elements to a fortuitous combination of fuch atoms: and yet fortuitous it seemingly must be if thofe elements are mutable and interchangeable, unless we fuppofe the Creator conftantly attentive to fupply their wafte, and keep up their number. Admitting, with philofophers, 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, exiftence. They must be regarded as organical molecules, whofe properties are permanent and immutable.

As thefe, however, are not the primary phyfical atoms, of which they are compounded, thofe permanent properties do not depend on the identical atoms of which they are compofed. Like other compound bodies, they may exift and preferve their own identity, during the conftant admiffion and difiniffion of their conftituent atoms; and therefore it is neceffary that fuch compound elements, however different from each other, should be formed of heterogeneous atoms.

The mistake feems to lie in fuppofing elementary and other compounds to be the mere refult of appofition and accretion of fimple matter; whereas they are the contrived combination. of complicated motions. The two fimpleft and moft general principles in nature are power and direction; the properties of all bodies whatever being the mechanical effect of thefe, refulting from their original difpofition by the Creator. Thus the action of every body in nature is mechanical, and its force a mere mechanical force; the direction of fuch force, or the combination of the mechanic powers, however, conftituting

fuch bodies, must be the effect of defign, immediately refulting from a firft caufe, and conftituting thofe properties in fuch elements as our author calls elective.-There requires nothing more, therefore, to fettle the difference between us and our author than that he make a diftinction between chemical elements and phyfical ones; not recurring to particular expedients to folve general phænomena, because they are neceffary to folve parti

cular ones.

We fhall readily give up to him the expediency of having recourfe 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 compofition of bodies in each, are more than mere accumulations or combinations of inert matter.

They poffefs properties, arifing from a contrived and permanent fyftem of motion, or a combination of powers conftantly and confiftently exerted in particular dire&tion. The peculiar properties hence arifing, however, by no means exempt them from, although in fome cafes they may counteract, the more general principles of phyfical action.-Having premited this, we fhall quote what Dr. Higgins obferves on the immutability of the primary elements of matter.

"I know not any doctrine fo injurious to the caufe of natural philofophy, as that, of the converfion of bodies; for it diverts men from the examination of what really happens to bodies in many interefting operations; and it flops all enquiry into the properties of the ultimate parts of matter; which enquiry is the most important of all that can engage a modern philofopher.

"As it is my purpofe rather to explain and recommend, than to enforce thefe notions concerning the parts and properties of matter, I omit a great number of observations, which might be offered in confirmation of them; and presuming that my readers will collect, from the following sections, feveral arguments to this effect, I shall conclude this part with the following remarks.

"As nothing lefs than a fupernatural agent can annihilate matter that is once created, fo nothing lefs can make the parts of air 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 affigned to them; or can cause the heterogeneal parts to exchange their properties: and as all the parts of the known fy item appear, fo far as we can difcern, to be governed by inceffant and immutable laws, and to be framed with fo much prefcience and wildom that they require no new alterations, regulations, or fubititutions, 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 figure and fize, and property of the fame at all times; and that the powers which

caufe

caufe the relations of matter, act inceffantly; and that most of the va. rieties obfervable in bodies, depend on the compofition and counteraction of these powers, during the combination of diffimilar parts of matter."

The attentive reader will fee, that if our author had confined his immutability of elements to thofe of the intermediate or fecondary kind, fuch as the elementary molecule or conftitucnt parts of natural bodies, inftead of extending it to the ultimate parts of matter in general, we fhould have had no objection to this part of his argument.-As it is, we fhould, totis viribus, oppofe his attempt to establish attraction as a primary property in the elements of matter, did we not conceive his affumption too precipitate, and his arguments too confufed to promise it any fuccefs. We fhall pass over, therefore, his ineffectual reprehenfions of Sir Ifaac Newton on this head, and his infufficient endeavours to prove him mistaken in matters; wherein his fagacity, like that of Lord Bacon, prophetically pointed out what innumerable experiments have fince ferved to confirm. Among thefe is, the existence of an univerfal elaftic 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 introduction, and come at length to his Obfervations on Light; the profeffed fubject of his Effay.And here again, we cannot help conceiving he makes a falfe ftop at the threshold. It is indeed, the misfortune of most of our chemical theorifts, that they are deficient in the principles of the mechanical philofophy. Hence it is that they fo often miftake fubftance for power, matter for motion, and vice versâ. At the fame time, also, they are apt to be too negligent of logical diftinctions and precifion of terms. Thus our author fets out, in his first chapter, to prove that a motion of light is neceffary towards illumination and vifion." He might almost as well have faid the motion of light is neceffary to its exiftence; in which he would have not been far from the truth, as light is in fact only a fpecies of motion.

"In a room encompaffed by opaque walls and floors, we have no vifual fenfe of objects nor of light; and we find that this darkness is either privation or quiefcence of light. When a body in the act of combuftion is brought into the room, we have visual sense of light and of the objects in the room; and hence we learn, that not only the prefence of light, but a motion of light, is neceflary towards illumination and vition. For, if we fuppofe 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, denotes 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 exifted previously

previoufly in every menfurable part of the room, and during the utter darkness of it; and that fince the quiefcence of Light is darknefs, the motion of light is the caufe of illumination, and we can fee objects only by light in motion."

What a pity, that our chemical philofopher was obliged to bring a body into the room, in the act of combuftion, in order to fet his light in motion! A North American favage might with two fticks of wood, or a country blackfinith with two pieces of cold iron, have foon made motion enough to produce illumination and vifion, without the aid of culinary

fire.

Such mere mechanical light-makers, however, might not have philosophy enough to know that, they could not fee in the prefence of light, without firft putting it in motion. They might be fuch fimpletons as to fuppofe the light abfent, when they were in utter darkness, and infolently arrogate to themfelves the power of making light! But we here learn from our learned doctor, that, whether we fuppofe the light projected from the luminous body or not, it was prefent; and lay quietly in the dark, till their stirring about put it into motion. We cannot help remarking, on this occafion, the extreme abfurdity, many of our philofophers are guilty of, in their abufe of words, in treating of light, fire, &c. A Mr. Jones of-Oxford, author of an Effay on the Principles of Natural Philofophy, published fome years fince, thus ufes fire, light, and ather, as of one and the fame meaning. "We must not imagine, faid that reverend phyfiologift, that heat and cold are different 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 quiefcent. 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 pyrophorus nor any other object is vifible; but when the pyrophorus expofed to air, enters into coumbuftion, it is vifible, and illuminates other objects. And fince the illumination continues whilft phlogistic matter is emitted from the pyrophorus, and ceafes when this emithion ceafes, and when the refiduary matter of the pyrophorus is dephlogisticated or incombuftible; it is evident that, if the light feen, be projected from the fubftance of the pyrophorus, it is feen 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 phlogitic matter which is certainly emitted from the pyrophorus.

"The phofphorus of Kunkel caufes no illumination, whilft it is kept in the Torricellian void, and whilst it is by any means prevented : VOL. VI.

M

from

from emitting its phlogifton. The fame phofphorus illuminates, more or lefs, as the quantity of phlogifton which elcapes from it, in a given time, is greater or lefs; and the illumination ceafes when the phlogiston is departed from the refiduary incombustible faline matter, which with the fresh phlogifton of any phlogiftic body is capable of forming phofphorus again. And fince the phofphorus is luminous only whilft matter is manifeftly moved from it; we clearly perceive that light at reft, whether in the phosphorus or diffused in the chamber, is not fenfible to us; and that the illumination caufed by phosphorus confifts in the motion of light emitted from the phofphorus, or in the motion which diffufed and quiefcent light receives from the moved phlogiston of the phosphorus."

Well, reader, what fay you to the pyrophorus of Komberg, the phofporus of Kunkel, and the phlogiston of Higgins? Do not the pyrophorus and the phosphorus, and the phlogiston illuminate your understanding, and make our author's light as clear as the fun at noon-day?-No! Attend then to a short argument, a little more obvious and mechanical. Light, properly fo called, is never either quiefcent or utterly dark. Where utter darkness prevails, Light is not prefent, but totally abfent. Light is a motion propagated, in vibrations, through that fubtle elaftic medium, which is intimately mixed with the groffer atmofphere, and is extended through the whole region of space; agreeable to the opinions of the beft modern philofophers Sir Ifaac Newton, it is true, for reafons favourable to his mathematical mode of treating the fubject, chofe to confider light as a body projected from the luminous obje&. This opinion has been, of courfe, adopted by almoft all the mathematical writers on the fubject; others have, with more reason, rejected it; among which is Dr. Higgins; who refutes not feebly the opinion of Sir Isaac on fuch fuppofed projection.

"The fluids which efcape from bodies during the combustion or decompofition of them, expand eccentrically from the bodies, by the repulfive powers of their parts. If light be combined in bodies, we know no other caufe of its emanation from them during their combination, except repulfive powers of its parts, funilar to the foregoing repulfive powers; and light flowing from bodies by fuch powers, and with fuch forces, would impel and move the bodies oppofed in its courfe, and especially those bodies which reflect light or are faid to stop

*Viz. Huygens, before Sir I. N. and Le Cat, Euler, and others fince. + The doctor should have faid efluvia; a fluid being rather an unitedly gravitating body, in the atmofphere of fome other lighter fluid; whereas the effluvia, projected from bodies during combuftion, or any other decompofition, are feparately floating folids in a fluid generally heavier than themfelves. Rev.