Oldalképek
PDF
ePub

THE

LONDON REVIEW,

FOR AUGUST, 1777.

A Philofophical Effay concerning Light. By Bryan Higgins, M. D. Vol. I. 6s. Dodfley.

(Continued from Vol. V. Page 134 *.)

In this age of philofophical improvement, when the moft interefting difcoveries in phyfics, promife a farther infight to firft principles, than the moft fanguine experimentalift bath hitherto dared to hope for, the purfuits, of every enquirer into the fecrets of nature, become a peculiar object of critical attention. We fhail, for this reafon, beftow a greater portion of that attention to the prefent work, than otherwife its bulk or fubject might feem to require. In opening this article in a former Review, we gave a fpecimen of Dr Higgins's manner of argumentation, in laying down the definitions proper to his plan, in the introduction to his Effay.

As a trifling flip at the threshold, however, may be of material confequence in the profecution of any intended creer, it is highly neceffary that it fhould be avoided or corrected

It is with great propriety Dr. Higgins obferves, in fettling the minima nature, or primary elements of bodies, that inde

The indifpenfable avocations, of the writer of this article, having obliged him hitherto to defer its continuation; as it has done that of fome other articles; which fhall fhortly be compleated.

VOL. VI.

L

finite

finite magnitude and infinite divifibility, however juftly applied by mathematicians in treating of inere extenfion, ought to have no place in phyfical enquiries. Ideal divifions, therefore, of palpable bodies fhould certainly be rejected. But in rejecting ideal divifins fhould not we alío reject ideal qualities?

"I confider," fays our author, "the fmalleft parts into which any mafs of matter is ever divided in the process of nature or art, as the ultimate parts of that mafs, and as fmall bodies. which are incapable of actual divifion or diminution. Thefe minute bodies are very aptly termed atoms; and ufing the term atom in this fenfe, I express by it no more nor less, than what really exifts." But what is this? Surely this is neither more nor less than a very equivocal mode of expreffion! Has an atom exiflence without effence? What is the property or quality of these indivisible atoms?-Are fuch atoms only finaller bodies? If fo, what conftitutes their primitive folidity? It has been maintained, with great reafon*, that the folidity of bodies is as mere a phænomenon as any other property attending them. If every condition, as our author terms it, of matter, "which is not deducible from experience, or neceffary towards explaining natural phænomena, is to be rejected," the supposed folidity, or impenetrability, of the primary elements, must be rejected; as being equally ideal with their infinite divifibility. Not that we mean to reduce fuch elements to mere mathematical points, or to difpute their exiflence; we only mean to enforce the neceffity of afcertaining their effence. And this may be more fully and fairly deduced from an argument a priori, than from phyfical experiment -The actual divifion, and thence the evident divifibility, of palpable bodies, into impalpable parts, is a fufficient proof that the particles, molecules, atoms, or whatever elfe our author chufes to call them, are fo minute as to elude the investigation of experiment, with respect to their magnitude, figure, or form. That they are folid or impenetrable, therefore, it is impoffible for us to know by experience; and that fuch folidity is neceffary to explain the phenomena of nature, cannot be granted, if fuch phænomena are to be more fimply and mechanically explained without it Sir Ifaac Newton, indeed, in his Regule philofophandi, lays down a rule, which may keep Dr. H. in countenance, while he concludes that the component elements of hodies muft poffefs the fame property as the bodies themselves. "We find," fays he, that feveral bodies are hard; and argue, that

[ocr errors]
[ocr errors]

* By Dr. Luzac of Leyden, and many other ingenious phyfiologifts.

the

the hardness of the whole only arifes from the hardness of the parts: whence we infer, that the particles not only of perceptible bodies, but of all others, are hard likewife." But is this a philofophical way of arguing Might not it be faid, with equal propriety, We find feveral bodies are foft, and therefore their primary particles, as well as thofe of all others, are foft too?" We will venture to affirm, with an able modern writer, that there never was, nor can be, an experiment made, froin which we can fairly infer, that folid or impenetrable elements, or atoms, exift in nature.

That refifting objects exift, we feel, and know. But that their refiftance is the effect of the abfolute impenetrability of their conftituent parts, we neither can feel, nor know. The hardness of palpable objects (and fuch only can come under the fcrutiny of phyfical experiment) is merely relative.

By experience we learn, that fome bodies are comparatively more foft or hard, penetrable or impenetrable, compreffible or incompreffible, than others; but, when we fhall have found the hardest and most compact body in nature, we fhall only have found a body that is impenetrable to others lefs penetrable. We have no means to make proof of its own absolute solidity; for, even the fubftance of foft clay is as impenetrable to foft clay as that of iron to iron. And the body which appears hard and impenetrable as iron to the gentle preffure of a foft hand, would appear foft and penetrable to the forcible impulse of a hand as hard as iron.

When Sir Ifaac Newton, therefore, inferred from the extenfion, hardnefs, and weight of palpable bodies, that the primary homogeneous elements of which all bodies are conftituted, must be extended, folid, and heavy too, he reafoned illogically; as well as took that for granted which he should have proved.

We do not, however, as before obferved, queftion the exiftence of fuch atoms; but what are they? To define a thing, by giving it a name, denoting neither more nor less than that it exifts, is no definition at all. That fuch primitive atoms do extend, or defcribe a certain quantity of pace, how fmall foever, is the neceffary confequence of their number, or plurality: even two mathematical points being neceffarily divided by fome pofitive diftance, which is divifible into at leaft three other points; as neceffarily divided by as many others. Either then the primary atoms muft feverally describe, or occupy, fome certain quantity of space themfelves, or they must be divided by fomething else that does. Now it is cer

[blocks in formation]

tainly more philofophical to impute extenfion to the primary elements themselves than to the mere medium of their divifibility. Every fuch atom muft of neceffity, therefore, occupy fome portion of fpace, or be of some dimenfions; but whether thefe dimenfions be fixed or changeable, whether fuch atoms may not be capable of dilatation and compreffion, are queftions no phyfical experiment can immediately decide. If we banish ideal conditions, and impute to things, barely found to exist, fuch qualities only, as they cannot be without, we fhall attribute to fuch atoms merely the property of expanfion or capacity of occupying the quantity of space, defcribed by them, and nothing more. This property, however, is, for the reafons before given, far from being that of folidity or impenetrability. It will be fimply that of a power of expansion; viz. that of refifting an equal expanfive force, being in contact with, or acting in a contrary direction.-And fuch, we prefume, are the primary elements, or atoms, of all material bodies.-It is not our business to fhew here in what manner the folidity and other phænomena of bodies mechanically refult, from the motion of fuch elements among each other. We have juft hinted at the only property, we can philofophically affign fuch elements, in order to fhew how liberal our author is in his poftulata of firft principles: even Sir Ifaac Newton being still less fo than Dr. Higgins. Sir Ifaac, indeed, prefumed that the primary elements were of a determinate form, folid, and impenetrable; but then he conceived them to be inert and inactive. Even their fuppofed innate power of attraction, he admitted, might be the effect of external impulfe. Dr. H. on. the contrary conceives the attraction of matter to be the innate and infeparable quality of the primary atoms.

"As we are convinced by experience, that the whole weight of any body, is equalled by the fum of the feveral weights of the fmalleit parts thereof which we can examine; and that the gravitation of any large body confifts of the gravitations of these parts; and as gravitation is never found to ceafe, by reafon of any further division of maffes; and as aerial and alkaline and other elaftic fluids do gravitate when their ultimate parts are held diftant from each other, as well as when thefe parts cohere and form folid ponderous bodies; it is realonably inferred that each atom of an heavy homogeneal mafs, doth gravitate according to the fame law which regulates the gravitation of the

mafs.

"la a variety of chemical operations we learn that the attractive powers, whereby maffes of earth or of acid and alkali, or of any other kind of matter, are combined or made to cohere, do operate to the fame effect on the fmalleft vifible parts of these maffes: and when the parts of folid bodies become invifible in folutions, we find the ultimate invifible parts are actuated by attractive powers, which caufe

them

thèm to unite and form vifible particles or large maffes, in proportion as the menftruum is withdrawn and in the mixture of invifible elaftic fluids which condenfe each other, we perceive that these attractive powers actuate the ultimate parts of fuch fluids, as well as the visible parts of the maffes which are formed of them: and thus we are authorized to conclude that each atom attracts according to the law which regulates the attraction of the body, confifting of any number of fuch atoms; and that the law of attraction which is discoverable in a body which we can examine, is the law of attraction of the homogencal atoms thereof, and of any one of thefe, which by reafon of its minutenefs we cannot examine."

We are by no means fatisfied with this method of reafoning, by induction, as our author terms it: nor are we clear that gravitating bodies may not be refolved into parts that will not gravitate. On the contrary, we have many good reasons, in the like mode of induction, to conclude, they may. In the next fection our author maintains, that "the atoms of matter are immutable in figure, and may, without fenfible error, be confidered as globular bodies!"-According to the fyftem above-hinted, thofe particles are mutable in figure, although they must, if at reft with respect to each other, affume an hexagonal one. The figure of bodies, depending on their property of folidity, we conceive to depend on the motion of their conftituent parts, as do alfo their texture and denfity; differing from the notion of Sir Ifaac Newton only as imputing that to mechanical impulfe which he imputes to phyfical attraction, a difference of no importance in the prefent cafe, as our ingenious chemift controverts both the caufe and effect, as laid down by that great philofopher. "Bodies, fays Dr. Higgins, are not mutable into each other, and the properties of the atoms of any elements are indefeasible."-Sir Ifaac Newton had faid, in his famous Queries, printed at the end of his Optics,

"Now the smallest particles of matter may cohere by the strongeft "attractions, and compofe bigger particles of weaker virtue; and "many of thefe may cohere and compofe bigger particles whofe virtue "is ftill weaker, and fo on tor divers fucceffions, until the progreflion "end in the biggest particles on which the operations in chemistry, and "the colours of natural bodies depend, and which by cohering compole bodies of a fenfible magnitude, &c."

"Much trefs is laid on this and the fubfequent paffage by those who imagine, that the fmallest phytical parts of matter differ from each other in no re pect; that by the union of two or more of these, particles are tormed pofieffing different properties, according to the num ber and arrangement of their parts; that fuch particles as are compofed of the fame number of parts, conftitute the portions of matter which I call Elements; and that particles confifting of unequal numbers of parts,

and

« ElőzőTovább »