Imatges de pàgina
PDF
EPUB

the press. He adds, that ' if by any sudden revolution of thie laws of nature; or by any fortunate discovery of those on the spot, it has really become that fertile and prosperous land, which some represent it to be, he begs permission to add his voice to the general congratulation.' – The reader will at once perceive that this mode of joining in congratulation, is, per. haps, not the most graceful, and too much resembles thofe old-fashioned accompaniments to doubtful intelligence, hum ! and ha!

Dissertations on different Subjeffs in Natural Philosophy. By

James Hutton, M. D. 410. Il. is. Boards. Cadell.

1792. W E are not unacquainted with Dr. Hutton as a philoso

W pher. In the Edinburgh Philosophical Transactions, he is the author of various dissertations, which display at least diligence and attention; and are ingenious, if not satisfactory. Dr. Hutton's Essay on the Theory of Rain, in the first von , lume of that collection, we noticed in our LXVIth volume, page 110, and there offered our reasons for thinking his system in part gratuitous, and in part inconiplete. This essay forms the first Dissertation in the present volume; and the second is a reply to the objections of M. de Luc, published in the Idees sur la Meterologie, which have appeared in the second volume of the Edinburgh Transactions. M. de Luc, though poffef. fed of no inconsiderable knowledge, is so wordy an author, his grains of science are so much overwhelmed with chaff, that we have seldom been able to follow him in a controversy.

The third Essay is connected with the former, and relates to winds, which are explained on foundations as uncertain, and on suppositions as hypothetical, as the phænomenon of rain. We shall not, therefore, resume the subject, but proceed to the other Diflertations.

The second part treats of the principle of fire. It is the chemistry,' obferves our author in his Preface, of those me. teors which give light and heat : it is the chemistry of that central heat, which actuates the mineral regions where our land is prepared; and it is the chemistry of that, which more immediately concerns us, in being the cause of animal heat." An author, unacquainted with Dr. Hutton's works, would read this paragraph with fome astonishment; with admiration, tempered with suspicion. To us the principal ideas were not new: they occurred in our author's Theory of the Earth, in the first volume of the Edinburgh Transactions, and were exSmined at no inconliderable length, in our LXVIth volume, . page 105

While Dr. Hutton was supporting the principle of a central fire, and directing its powers in the performance of the most important operations, he must feel feverely the ruin which threatened the whole, by the destruction of its principal foundation, phlogiston. The tortoise must be supported, or the elephant, and its precious load, the earth, must fall. Perhaps the system, in a proper view, might not be much endangered by the result of the inquiry, whatever was the decision; but our author wanders round it without any clear ideas--we must follow him. Infiammable bodies certainly differ from those which are uninflammable ; but in what do they differ i-do they poffefs only sensible or latent heat, or do they derive, from the solar influence, another principle, by which they are diftinguished? The object is to show, that there is another principle, and that this principle is the old, deserted phlogiston.

The modern term caloric, our author considers to be heat cither sensible or latent; but the purpose of his

• Paper is to Mhow, that some important facts, or effential pheno mena in the burning bodies, are not explained in the antiphlogistic theory; and that, until these be explained, it must be necessary to retain the term phlogiston, which expresses something material in the knowledge of nature, or generalizes certain phenomena, which the new theory does not explain,

"The do&rine of phlogiston may be considered as implying, that a quantity of the matter of light and heat is occasionally contained in bodies, as a part of their composition; and that those phlogistic bodies possess this naturally diffufive substance, upon a different principle from that of heat, or any other besides this which is peculiar to itself,

There is no question at present, how far this was precisely the idea of the chymists who first introduced that term; or if, on many occasions, the term phlogiiton has been misapplied, before the nature of the feveral aeri-form compofitions was known. We have only in view, to endeavour to retain the term of phlogiston where it may be properly applied, and to show the defect of the new theory, which does not explain an important part of natural phenomena, or which rather attempts to explain it by a principle which will not apply.'

We think his error is obvious from this statement. Caloric is not heat, either sensible or latent. It is an abstract term for the matter of heat : in other words, the principle, in conse. quence of which heat is, or is capable of being, evolved from different bodies. It is clear, that the heat, produced in burning borries, does not wholly arise from the body burnt, but from the surrounding air ; that the change produced by burn

E 3

i inga

authern schools of chle, in dispute.Crations, Dr. He conveyed by

‘ing, is as much the consequence of the addition of one prina ciple, as of the abstraction of another; that no heat is con, ferred by the folar influence, except so far as it is conveyed by light. Independent of these considerations, Dr. Hutton seems to mistake the principle, in dispute, between the old and the modern schools of chemistry. The one supposed, like our `author, a principle in bodies, the presence of which rendered them inflammable, and its absence uninflammable: the other showed that the purest and least compound bodies were inflammable, and the most compounded in the opposite state, so the consequence was, that burning consisted in the addition, rather than in the deprivation of any ingredient, and this addition they found to be air in a peculiar form. Again: our author endeavours to show, that his phlogiston is distinct from every species of heat, yet it only appears, fo far as we can perceive, by properties connected with the inflammable state. It is supposed also to be a peculiar modification of the solar substance, though we know nothing of solar influence, except as light, which it certainly imparts, and as sensible heat, with which it is perhaps more remotely connected.

'The two great difficulties which perplex our author, are the distinction between heat, occasionally evolved, and latent heat; secondly, the decomposition of water. He labours to explain the first with great care ; and having shown that heat some times evolved is not latent heat, while it certainly in its former state was not sensible, it must be phlogiston. Dr. Crawford's work, with the Memoirs of M. Lavoisier, would soon explain the difficulty: latent heat is occasionally received and discharged, with an alteration of form only ;-the caloric, on the contrary, is an ingredient, on which the essential properties of bodies occasionally depend. The second difficulty we cannot elucidate, as it depends so much on the nature of the experiment, every part of which Dr. Hutton misapprehends. The composition and decomposition of the supposed phlogif. ton, relate only to inflammable air, which the modern chemists have completely illustrated. .. The third part consists of physical dissertations on the pow.ers of matter and the appearances of bodies, chiefly tending to support the existence of the favourite phlogiston; and the first dillertation is on the laws of matter and motion ;-in other words, an inquiry into the nature of physical body, its constitution, qualities, and accidents. Had our author pursued this subject, without the bias of a theory, science might have gained by the investigation. Our ideas of matter, and of its different properties, require a new investigation, unfettered by the trammels of the old mechanical philosophy. : It was too much the custom of philosophers to consider matter in the

bulk

monice.

bulk, and too little in its minuter parts. On this subject, our author's observations deserve notice.

• But, before we proceed to investigate those powers of bodies by which their qualities may be changed, it will be proper, in the next dillertation, to take a view of that general quality of bodies by which they naturally change their places in relation to each other, a quality which has been most succefstully generalised, although perhaps upon some principles which, according to the theory of matter now to be given, cannot be adınitted.

"Therefore, before proceeding to that subject, it will here be proper to mention those principles or opinions which are now alledged as having been improperly employed in generalising gravity. We shall thus have an opportunity, in this preliminary dillertation, of examining certain fundamental principles of great importance in natural philofophy, principles which are to be employed in the following physical inveitigations.

. First, then, the received philosophy says, that matter, as the elementary subítance of bodies, obeys the law of inertia. This doctrine, I apprehend, is either a milupplication of the term inertia, or a mi underst.ndirig of the term matter. One thing is certain; it is not in the maiter, which const tutes natural bodies, that the law of in rtia has been investigated, but in the bodies themselves. Therefore, to far as there is a distinction made of bodies and the matter of which those thin s are composed, there is not any evidence of inertia being proper to the matter. It must also appear, that, so far as there is no distinction made of bodies and their mutter, there is no objection here intended to the use of the term inertia, as commonly understood.

. Perhaps it may be thought that this is but a triling difference, or a frivolous distinction; and that, the law being acknowledged, it is of little consequence whether, in the exprefsion of it, the terın mci. ter or body be employed, especially as philosophers seem to be fo little agreed about the distinction of thoie two things which, in this case, only form the subject of dispute. To this it must be replied, that it is in forming the necessary distinction of matter and body, that the error of expresion is discovered; and that it draws to an important conclusion, when matter, as the principles or constituent substance of bodies, comes to be investigated ; for, perilaps, it may be found, that there exists a certain ipecies of matter not subject to that law of inertia which we are to examine; perhaps it may be found, that no species of matter, striály speaking, is inert, as poiterfing that property which is so confpicuous in bodies. But, in either of these cases, natural philofophy must appear to have proceeded upon a false principle, in having reasoned upon zertia as an univertal, in relation to matter as distinguished from mind, or even as distinSilhed from body.

• Secondly,

E 4

Marily for its gravitacionly faying all the

• Secondly, the received philosophy says, that all matter gravitates; for, having (gratuitously indeed) endowed all matter with the property of inertia, it is thus found, by an easy experiment, that all the inatter of a body must have weight. But this is only saying, that the inertia of a body is in proportion to its gravitation. Now, this may truly be, without it necessarily following, that all the matter which enters the constitution of a body, should be actually endowed with inertia and weight. I hope that I have show, in the preced, ing differtation, that all matter does not gravitate. But this is a point upon which hangs the system of physics, which is to be proposed in the subsequent dissertations; and the truth of this affertion will therefore depend upon the consistency of that system with the natural appearances of things, or upon the explanation that may thus be given to the natural phenomena.'

We fully agree with Dr. Hutton, that inertia is a property of body; but we must add, that he has not shown inertia to be inconsistent with matter. We certainly know nothing of matter, but as a divisible part of body; for, in the decomposition of compounds, we arrive at what, in any other ftuation, would be called body, and the minutest parts of elementary bodies fill possess the same properties. What therefore is predicated of the largest, must be of the smallest portions, though the converse of the proposition is not true, fince the smaller particles appear to be actuated by relative powers, though still obedient to the general ones. Thus the smallest particles of an acid and alkali, seem to be active in their mutual unions: the molecules of salts seem to unite by a predetermined election, yet they are still particles of matter, and each subjected to the law of gravity.

Dr. Hutton entangles himself also in discussions respecting gravity. 'He forms the net by his definition, and proceeds with difficulty in the confused outline. He seems willing to deny, that gravity is an universal principle, and expresses himself in a manner at first equivocal, with respect to the extension of gravity to the celeslial bodies. • Gravity, he remarks, is that power by which a body feels heavy, when supported by the hand, or by which, when unsupported, it falls to the ground.'

This is an unfair view: gravity is only, on a larger scale, the mutual attraction of bodies. Were the projectile force of the earth defroyed, the sun and earth would unire by the force of gravity, but the point of mceting would be as near to the fun, as the sun is greater from the earth. Had our author, followed this Newtonian view of the subject, much of his future discullion might have been spared. We shall notice only. one paragraph:

More than one place in space being thus conceived, we acquire.

the

« AnteriorContinua »