Imágenes de páginas
PDF
EPUB

Christianity, if a proper article for a work of this kind, needed not to have been extended through feveral pages, befide a variety of details under the refpective words Popery, Calvinifin, Methodism, Prefbyterianifm, &c. But it is abfurd to spend a number of pages on an hiftorical and geographical account of Hell, at the end of which the reader is referred to the word Elyfium. This reference to contraries, however, frequently occurs; as Cierg), fee Laity; Drink, fee Food; at the end of the long treatile of Fire we are again fent to Hell.

Among other matter, foreign to either the arts or fciences, we may justly rank the following: Burning-bufb, that bush wherein the Lord appeared to Moies,' with the fubitance of that chapter in Exodus where the tranfaction is recorded. Beard, the hair on the chin, fee Hair. Turning to Hair, we find a long treatise about it, and at length are referred to the word Peruke, which however does not occur in the book.

A minute examination of every article in a production of this kind, is a task which we never propofed to ourselves, and which we are fure our learned Readers would not require at our hands: yet, confidering the nature of the work, its price, and the promifes made in the Preface, we have been induced to give it as much attention as perhaps it deferves, in order to fulfil, to the utmost of our power, the obligation we are under to the Public, of painting out the merits or faults of literary performances, efpecially fuch as are fo extremely voluminous, and rated fo highly as the prefent. The extenfive plan of this Dictionary is one of its greatest faults; and we are perfuaded, that were this enormous work divided into a number of fmaller ones, imperfect as the matter is, it would be more useful to the Public, and more advantageous to the proprietors. There are some parts of it which we muft acknowledge to be well executed; yet the whole is of too great a bulk, as the compilers themselves have evidently experienced; for the first volume contains only three fourths of the letter A, and the tenth S, T, V, U, W, X, Y, Z, befide a copious Appendix and Index. This circumstance alone fhews the inequality of the work, and how much the compilers wifhed to finish what they foon found was likely to extend its bounds too far.

In reviewing fo large a work, we think it our duty to fay fomething concerning the manner in which it is printed. To enumerate all the typographical errors that occur, even in the articles we have perused, would be a laborious tafk; and the many inftances of negligence are evident marks of hafte,and inaccuracy. The continuing to number the pages from the beginning of the work to the end, through the whole ten huge volumes, is unufual. The Editor however has adopted an excellent contrivance, which fhews his fk ll in the bibliopolian art. Although

the

[ocr errors]

the pages are numbered from the beginning to the end, yet the feveral treatifes which we have mentioned are paged feparately. For inftance, Mufic, which comes in after 5264, is paged 1, and the numeration goes on to 60, where Mufic ends, and the page after is 5265; fo that the treatife may be taken out of the Dictionary, and not miffed, and fold as a book by itself; a complete treatise on Mufic, on a prefixed title page, being the only thing wanted to render it a perfect book. The copperplates, which are three hundred and twenty-three in number (though the title page only fays above two hundred'), are, in general, poor engravings; in many inftances they are bad reprefentations of the originals; and in fome, particularly the botanical ones, material faults occur.

[ocr errors]

Upon the whole, we wish that Arts and Sciences had fome better fupport than they are likely to receive from the prefent performance; yet for many obvious purpofes, the Encyclopædia Britannica may be ufeful, and afford much inftruction. In its prefent ftate, however, it may, not unaptly, be compared to a great garden, abounding with choice trees and plants, but all over-run with weeds.

R

m.

ART. V. An Efay on the Investigation of the firft Principles of Nature: together with the Application thereof to folve the Phanomena of the Phyfical Syftem. Part I. Containing a new philofophical Theory, &c. By Felix O'Gallagher. 8vo. 5s. Boards. Murray. 1785.

[ocr errors]

HIS work is delivered in the form of lectures, beginning with the first principles of philofophy, and laying down a theory and rules for phyfical inveftigations. The first and fecond fections confift of what the Author calls the first principles and fundamental axioms of natural philofophy, neceffary obfervations, and phyfical definitions and propofitions: but we cannot pretend to give a particular account of thefe, which would take up too much room.

In the 3d feat. the Author compares the Newtonian rules of philofophizing, as given by Martin in his Philofophia Britannica, vol. i. p. 2.; with his own rules, or propofitions, delivered in the two former fections, whofe fole tendency, he fays, is to form accurate diftinctions, which is in a great measure the busi nefs of philofophy.'

The fpirit of Newton's rules, on the other hand, is to fimplify, and, if poffible, to deduce all effects from the fame caufe: which method, however juft, was dangerous in its application, as it induced his followers not to fearch after, nor admit more principles than one, although more manifeftly difplay them felves in nature. Two examples will fhew the different tendencies of both methods. Conformably to the fpirit of the Newtonian rules, it is faid (by Mr. Martin) in the general conclufion, that all bodies confift of one

and

and the fame kind of matter, and that all their varieties proceed from various modifications of the fame particles. It is alfo concluded, in the explanation of the third rule, that gravity, vis inertiæ, &c. are the properties of all bodies. But our rules not only render us more circumfpect in adopting fuch conclufions, but even induce us to reject them. For as to the firft, we know that the immediate and phyfical caufes of all material effects are themselves material; that therefore the cause of heat, light, and expanfion, or the fubftance, producing thofe effects, is material. Again, as one phyfical agent, or material caufe, cannot produce two contrary effects; therefore attraction, which draws together, and expansion, which separates, cannot proceed from the fame caufe. Confequently, as thefe two operations are feen to obtain in material nature, they have two diftinct material causes, whofe effences and propenfities are oppofite; we therefore difallow the general conclufion above cited from Martin, and pronounce that experience exhibits, at leaft, two kinds of matter in nature for oppofite propenfities muft arife from different effences, i. e. different fubftances, confequently from different principles.

Let us now, according to the fame method, examine the second affertion we have quoted, to wit, "that vis inertia, with the other properties there enumerated, is common to all bodies."- Certain it is, that a strong centripetal force acts upon bodies throughout the univerfe. It is alfo allowed, that there is also another power in nature, namely, that of fire or light, which expands or dilates bodies, feparating their parts with a centrifugal force. This principle of expanfion, according to Boerhaave, is fo univerfal, that there is not a body, or space in nature, which has not its fires, though fometimes latent until excited-Wherefore light or fire, the principle of the centrifugal force, being a material fubftance, we alfo conclude, that the centripetal force, which is equally powerful in producing material effects, alfo arises from a material substance.

There are, therefore, in nature, two material agents, of prodigious efficacy, and of oppofite propenfities or tendencies to act; thefe cannot be called inert, because they have in themselves a power of motion and of action, which gives motion to inert matter, and which produces the operations of nature. We must therefore fet limits to the property of inertnefs, which the prefent generalizing method of philofophizing has rendered too univerfal.'

So far our Author: but what Newtonian philofopher ever denied the efficacy of gravity, and fire? As to the inertnefs of matter, which Mr. O'Gallagher makes the subject of his fecond lecture, he calls the univerfality thereof, an unreasonable and falfe fuppofition; becaufe matter is defined by philofophers to be a fubftance extended, folid, and perfectly inactive, confidering how far this definition is juft, he allows it extenfion and folidity, but not inactivity, for then, he fays, we could not be fenfible of its exiftence; at least we should have no fenfation of those bodies which are beyond the reach of feeling: for fuch diftant bodies only affect our organs, which are of a neutral paffive nature, either by the action of an effluvium, or of fome intervening me

dium. Now, our corporeal organs being matter, can only be affected by another material fubftance, and this cannot be inert as it acts upon them: the matter therefore which gives fenfation of diftant bodies cannot be inert.'

But we apprehend that this metaphyfical mode of argumentation only mifreprefents the meaning of the Newtonian philofophers. No fooner is matter in motion, than we fuppofe they will allow that its inactivity is at an end. Our Author, however, goes further, and will not allow it to be inert even at reft. We cannot pretend to tranferibe the whole of what he says upon this fubject, or even to abridge it, but must refer to the book itfelf. He objects, at p. 80, to the ufual proof of inertness drawn from the motion of bodies on horizontal planes; and, at p. 83, propofes the following teft, which, he fays, admits of mathematical demonftration; we therefore fuppofe that he looks upon it as his principal argument.

Let a box or canister, wherein different weights may be put occafionally, be fufpended like a pendulum, at different lengths proportioned to the weights contained; if you allow a foot from the point of fufpenfion to the centre of the box, when a pound is in, allow twenty feet for twenty pounds, fo that the pendulous lengths fhall be as their weights. Let an hook or wire be inferted at the central part of the box or canister, to which a thread is fixed that will stretch horizontally over a free pulley; and at the other end of this thread let a fcale be joined, to receive the weights or grains that will draw the box afide from the vertical line of free fufpenfion; then note the weights or grains that will draw the central part of the box, when loaded with each weight, the length of an inch, or even the tenth of an inch from that vertical line, and you have the force of inertnefs in each weight, expreffed by the grains that move it from that line: for whatfoever moves the body overcomes its vis inertia.

[ocr errors]

Now (p. 86.), when thefe experiments are accurately made, and every circumftance confidered, and duly valued; if the difference of forces to ftir thefe two bodies, one of a pound, and the other of twenty pounds, whofe difference is nineteen pounds, is found to be but a few grains, which may be occafioned by the refiftance of the air, or fuch extrinfic causes, vis inertia may be confidered as the fame in all bodies, and therefore to be neglected in every computation, being a conftant invariable quantity in all heavy bodies, great and fmall, which admits of no various degrees, increment, or force.'

But will not the Newtonian philofophers fay that our Author is here combating a mere chimera, a creature of his own ima gination, and that they have no other idea of the vis inertia, but that the leaft imaginable impulfe, or accelerating force, will overcome it in free space? It is true, they will fay, that they fuppofe it greater as a body is greater, and for this reafon, if a heavy perfectly fmooth body be laid upon a finely polished borizontal plane, any heavy body connected with it by a ftring paffing over a pulley at the edge of the plane, and hanging freely,

may,

may, abftracting from friction, move it, nay draw it to the end of the plane but that the greater the body or weight is that hangs freely, the fooner will it perform this, yet fill in all cafes the defcending weight would move flower than it would do if the ftring were cut and it were liberated from the body that moves along the plane; confequently the vis inertia acts as a retarding force to the defcending body; and this body being fuppofed given, the greater the other body is, the greater is the retarding force, and is therefore different in bodies of different fizes or quantities of matter. As to this gentleman's propofed demonftrative experiment, they will fhew that it can be of no use or force at all. For any impulfe or force whatever acting horizontally upon the body, will be fufficient to draw it from the perpendicular, and the inftant it is fo drawn, gravity will begin to act upon it, and its own weight and the different pofitions of the ftring are neceffary to be taken into confideration, in order to determine how far it can be drawn from the vertical line; confequently, the experiment must be very ill contrived to determine with precifion the vis inertia.

His third and fourth lectures are on the elastic principle in bodies, which he fhews to exist in vegetable, animal, and foffil bodies, in fire, air, and water. He endeavours to exhibit the elaftic fubftance feparately, to fhew its ufes in nature and mode of operation. He takes into confideration a heap of vegetables 20 hundred weight, which is by fire reduced to a small heap of faline afhes, not 50, perhaps not 20 pounds weight, which when depurated, by wafhing, to pure pale afhes, will be much lefs: and perhaps, fays he, 10 pounds of fuch a refiduum would not remain, if the heap originally confifted of paper, or linen. He afks what is become of the weight or gravity of the heap, when its afhes retain not the hundredth part thereof?

Nineteen hundred weight, he continues (p. 157.), has difappeared; fhall we therefore conclude, that all this weight has been carried off by fmoke and flame? This feems improbable; for, whatever be the material cause of gravity, certainly it has not a tendency to afcend, being convergent and centripetal. On the other hand, flame has ever a contrary propenfity, viz. to rife and expand; and fmoke, which we find to be the nafcent form of flame, is analogous thereto, and fhould have the fame tendency, though in a lower degree; confequently, when fire diffolved the cohesion of the body, and feparated its elements from each other, -each purfued the propenfity peculiar to its nature; the elaftic matter, released from its confinement, fled into the atmosphere, its proper refervoir; and the matter of gravity must have funk with native propensity towards the centre of the earth, a fmall part of it only ftill remaining with the afhes and falts on the furface. And as effences muft ever accompany their peculiar fubftances, the elaftic matter in its fight, carried off the elafticity, fell, tafte, and other lively qualities peculiar thereto, along with the oils and spirits, on which, according to all chemifts,

the

« AnteriorContinuar »