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contained nothing very new or important; and we have seen others, particularly of late, that conveyed some of the most interesting intelligence to the public, that experiment ever extracted from the receffes of the material world, What is the average degree of excellence that may belong to such publications, and whether the prefent memoir falls fhort of that standard, or exceeds it, are points which we are not competent to decide.

The preface to these observations, besides informing us of the circumstance just mentioned, makes us acquainted with the view which Mr Vince had, in this examination of the systems, contrived for explaining the phenomena of gravitation.

. In his Optics, Sir I. Newton attempts to account for gravity by means of an elastic Auid. This, however, he proposes by way of a question, not being satisfied about it, as he says, for want of experiments. These, however, he never made; nor has any one since examined his hypothesis, in order to discover whether it will account for the law of gravitation ; for it is not sufficient merely to show that such a medium may exist as will drive a body towards the

To this is annexed the following note.

• Mr MACLAURIN observes, that this hypothesis no way derogates from the government and influences of the Deity, whilst it leaves us at liberty to pursue our inquiries concerning the nature and operations of such a medium. And Sir J. PRINGLE, the late worthy and learned President of the Royal Society, who executed the duties of his high office with great impartiality and honour, considering the importance of the subject, recommended it as deserving the attention of philo. sophers.'

Our author then goes on in the text to remark,

• What Sir I. Newton left for further examination, will be deemed no impertinent nor useless inquiry; more particularly at this time, when many of the most eminent philosophers upon the Continent have been endeayouring to account for all the operations of nature upon merely mechanical principles, with a view to exclude the Deity from any concern in the government of the system, and thereby to lay a foundation for the introduction of Atheism. Upon this account, the author was requested to consider the subject, and give the result of his examination. The inquiry was favourably received; and it was suggested, that it might not be improper to be offered to the Royal Society.'

On comparing the last of these pafliges with the first, and also with the note subjoined to it, a very obvious inconsistency appears. It is plain, that Newton, whole piety no man ever questioned, did not think that, to ascribe the phenomena of gravitation to a mechanical caufe, had the flightest tendency to support atheistical opinions, or to weaken the arguments for the existence of God and of Providence. Maclaurin and Sir John Pringle, were also of that opinion ; and, from his manner of quoting their authority, we fhould suppose that our author himself was of the fame way of thinking. Yet he immediately gives us to understand, that his inquiry was undertaken for the express purpose of trying, whether religion might not be supported, and the atheistical opinions, which he ascribes to the philosophers of the Continent, opposed, by showing the insufficiency of mechanical principles to explain the law of gravitation. In the same breath, therefore, we are told, that to affign a mechanical cause of gravitation, is quite consistent with the truths of natural religion; and also, that to disprove the existence of such causes, is a direct way of supporting those truths. It is equally out of our power to afGgn any other meaning to the paffages just quoted, and to account for the inconkistency which they involve. make it doubtful whether it be what is really meant); and that of Boscovich is not so much as mentioned.

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Again, it must be obvious to every one, that the belief in the mechanical cause of gravitation, which was so consistent with the piety of Newton and his countrymen, is represented as one of the weapons by which the philosophers of the Continent are at this moment attacking the whole system of religious belief. It would Seem, then, that an argument which an English philosopher may maintain in perfect consistency with theism, and all the great principles of natural religion, cannot be viewed, in the hands of his brethren on the Continent, but as atheistical and impious sophistry. We muft-look, it seems, not to the argument, but to the man that uses it; and not to the man only, but to the country in which he lives; because an opinion that is sound and orthodox in England, may be impious and atheistical in France or Germany. We know not how to afcribe such illiberal and inconsistent notions to this learned Professor, but cannot interpret his words in any way by which these conclufions can be avoided.

For our part, being convinced that the issue of this argument is quite immaterial to the truths of natural religion, which must Test on the same immoveable foundation, whether the physical cause of gravity is ever discovered or not, we feel no other interest in the result, than that which the extension or limitation of knowledge is calculated to excite. We must also express our hearty disapprobation of every attempt that is likely to confine the range of our inquiries, and to produce an intolerance of philosophical opinion. In all ages, there have been men illiberal and narrow-minded enough, to think that the search after natural causes was irreverent to the Author of Nature, and argued a doubt of his

power. Anaxagoras, though the first of the Greek philofophers who entertained rational notions concerning the Supreme Being, yet, because he was a great inquirer after second caufes, was accused of irreligion. The same charge, on the fame ground, has often been

renewed

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Concerning the system of Descartes, it was not neceffary to enter into much detail ; and Mr Vince has very properly abstained from doing so. The vortices of that ingenious theorist have long ceased to afford satisfaction even to the most fuperficial reasoner. They are known now only in the history of opinions, and, in that history, will ever furnith a most inftructive chapter. The manner in which the system sprung up at the dawn of science, flourished on the ruins of the school philosophy, and faded of itself in the brighter light of experiment and observation, is the best proof of the superior value of the inductive philosophy which 'Descartes so unwisely affected to despise.

A very just remark made by Mr Vince on the system of Defcartes, and on all others that depend on the same principle, is, that the planets being carried in vortices round the sun, the quantity of matter in the sun will not affect the velocity of the vortex, or the bodies immersed in it, inasmuch as that velocity might be the same, though there were no central body whatsoever. The quantity of matter in the sun, therefore, cannot enter at all as an element into the expression of the force by which the planet is impelled toward the sun. Therefore, as the fact is, that the quantity of matter in the central body does enter as a most material element into the expression of the gravitation of the planet, 'it is impossible to ascribe that gravitation to the action of a vortex. This argument is perfectly conclusive. It was not to this, however, that the system of vortices really owed its downfal, but chiefly to another, which Maupertuis has very well stated in his Differtation on the Figure of the Heavenly Bodies, viz. that whenever you suppose the vortex so arranged, that it will explain one of those great facts in the planetaTy motions, known by the name of Kepler's Laws, it becomes quite inconsistent with the rest.

The next system that was imagined for explaining the law of gravitation, was that of an elastic ether, mentioned by Sir Isaac Newton in the Queries at the end of his Optics, and proposed with such modefty and diffidence, as entitles it to great indulgence. It is the conjecture of the philosopher, who had demonstrated the existence of the law of gravitation, concerning the mechanism by which this universal tendency is produced ; and seems to be thrown out with the view of preventing those who followed him from thinking that it was sufficient to say that gravitation was an essential quality of matter, and that there was no occasion to trouble themselves about the cause of it. It was to serve as a stimulus to future inquiry, and as a caution against fupposing that the fabric of physical astronomy was complete. According to it, the mutual tendency of bodies toward one another, arises from the action of a fluid highly elastic, diffused through all space, but more rare within bodies than without, and more rare at a smaller distance from them than at a greater Bodies are propelled through this fluid from the denser to the rarer parts, that is

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, from the parts where the elasticity is greater, to those where it is less. Thus, with respect to the earth, the elasticity of the circumfused ether being greater at a distance from that body than near it, other bodies would, by that greater elasticity, be urged toward the quarter where the elasticity is less, that is, toward the earth. The same would hold of the sun and moon, and all the great bodies of the universe. This hypothesis, to which it must be confefled that many objections may be made, appears to have been suggested to Newton by the phenomena of optics, which it is better calculated to folve than those of astronomy. That a subtle fluid existed, and was diffused through those spaces from which air was exhausted, appeared to him evident from many confiderations, and particularly from this, that a thermometer in vacuo will grow warm almost as soon as a thermometer not in vacuo. Is not the heat, therefore,' said he, of a warm room conveyed through the vacuum by the vibrations of a much subtler medium than air, which, after the air was drawn out, remained in the vacuum ?' Again, he says, ' Doth not the refraction of light proceed from the different densities of this ethereal medium in different places, the light receding always from the denser parts of the medium towards the rarer? And is not the density thereof greater in free and open spaces void of air and Other gross bodies, than within the pores of water, glass, crystal, and other compact bodies? For when light passes through glass or crystal, and, falling obliquely upon the further surface thereof, is totally reflected, the total reflection ought rather to proceed from the density and vigour of the medium without, than from its rarity and weakness. Now, in applying this fluid to account for the gravitation of diftant bodies toward one another, he fuppofes, as before stated, that its density, and, of course, its elasticity, increases as you recede from the sun and other great bodies; that it is less within than at the surface ; less there than at a small distance from it, (as the phenomena of optics seemed to require); and that it goes on continually, though flowly, increasing. Though this increase of density,' he adds, may be exceeding flow at great distances, yet if the elastic force of the medium be exceeding great, it may suffice to impel bodies from the denser parts of the medium towards the rarer, with all that power which we call Gravity.' Optics, Query 21. &c.

Various objections may be undoubtedly offered to this hypothe{is ; and Mr Vince dwells particularly on one deduced from the

impossibility

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