contained nothing very new or important; and we have seen others, particularly of late, that conveyed fome of the most interefting 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 fuch 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 thefe obfervations, befides informing us of the circumftance juft 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 fluid. 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

sun. '

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 philosophers. '.

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 endeavouring 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 laft of thefe paffages with the firft, and alfo with the note fubjoined to it, a very obvious inconfiftency appears. It is plain, that Newton, whofe piety no man ever queftioned, did not think that, to afcribe the phenomena of gravitation to a mechanical caufe, had the flighteft tendency to fupport atheistical opinions, or to weaken the arguments for the existence of God and of Providence. Maclaurin and Sir John Pringle,

were

were allo of that opinion; and, from his manner of quoting their authority, we fhould fuppofe that our author himfelf was of the fame way of thinking. Yet he immediately gives us to underftand, that his inquiry was undertaken for the exprefs purpose of trying, whether religion might not be fupported, and the atheiftical opinions, which he afcribes to the philofophers of the Continent, oppofed, by fhowing the infufficiency of mechanical principles to explain the law of gravitation. In the fame breath, therefore, we are told, that to affign a mechanical cause of gravitation, is quite confiftent with the truths of natural religion; and alfo, that to difprove the existence of fuch caufes, is a direct way of fupporting thofe truths. It is equally out of our power to affign any other meaning to the paffages juft quoted, and to account for the inconfiftency which they involve.

Again, it must be obvious to every one, that the belief in the mechanical cause of gravitation, which was fo confiftent with the piety of Newton and his countrymen, is reprefented as one of the weapons by which the philofophers of the Continent are at this moment attacking the whole fyftem of religious belief. It would Teem, then, that an argument which an English philofopher may maintain in perfect confiftency with theifm, 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 must look, it seems, not to the argument, but to the man that ufes it; and not to the man only, but to the country in which he lives, because an opinion that is found and orthodox in England, may be impious and atheistical in France or Germany. We know not how to afcribe fuch illiberal and inconfiftent notions to this learned Profeffor, but cannot interpret his words in any way by which these conclufions can be avoided.

For our part, being convinced that the iffue of this argument is quite immaterial to the truths of natural religion, which muft reft on the fame immoveable foundation, whether the phyfical caufe of gravity is ever difcovered or not, we feel no other interest in the refult, than that which the extenfion or limitation of knowledge is calculated to excite. We must alfo exprefs our hearty difapprobation of every attempt that is likely to confine the range of our inquiries, and to produce an intolerance of philofophical opinion. In all ages, there have been men illiberal and narrow-minded enough, to think that the fearch after natural caufes was irreverent to the Author of Nature, and argued a doubt of his power. Anaxagoras, though the firft of the Greek philofophers who entertained rational notions concerning the Supreme Being, yet, because he was a great inquirer after fecond caufes, was accused of irreligion. The fame charge, on the fame ground, has often been

G4

renewed

renewed fince. It would be right, however, that those who bring this charge would take fome trouble to draw the line which feparates the legitimate domains of science from the hallowed ground which must not be prophaned by philofophical research. This boundary, we are perfuaded, it will be found very difficult to adjust. No one will fay, that it is wrong to inquire into the cause of elasticity, hardness, tranfparency, and fuch like qualities of body. Why, then, fhould it be improper to inquire into the caufe of gravity? On what principle is it, that it is lawful to feek for the mechanism by which the former effects are produced, and impious to extend the fame inquiry to the latter? If, indeed, gravitation were not only known to be univerfal among material fubftances, but if all the other caufes of motion could be reduced to it, and fhown to be modifications of one and the fame law, there would be little reafon to expect, that we could ever carry our inquiries much further; and, though we fhould not think that there was any impiety in the attempt to do fo, we fhould certainly defpair of its fuccefs. But our knowledge of gravitation has by no means reached this perfection. We are not fure that it is quite univerfal,-that heat and light, for example, are fubject to its power,-and, what is of more importance in the prefent queftion, we are fure that all the causes of motion have not yet been reduced to one; fo that gravitation is neither shown to depend on impulfe, nor impulfe on gravitation. Two laws, very different from one another, direct the motions of the material world; and, till thefe two can be reduced to one, or shown to depend on the fame caufe, or till they be demonftrated to arise from different caufes, our knowledge of them remains incomplete. Till every poffible means of effecting one or other of these purpofes has been tried,-till reafon and experiment can fairly be faid to have done their utmoft, philofophy has not reached its ultimate object. Some important fecret may ftill be within our reach; fome new proof of the fimplicity of nature, and of the wifdom of its Author, may yet remain to be difcovered. In the prefent ftate of fcience, we think it cannot be affirmed that the utmoft has been done with refpect to the object we are treating of; nor are we entitled to fay that the attempts made have been all completely abortive. This laft, however, it is the object of Mr Vince to prove in the paper before us; but his enumeration of thefe attempts, as we fhall foon fee, is much too incomplete to

authorife the conclufion which he has drawn.

The fyftems for explaining the caufe of gravity which Mr Vince examines, are thofe of Defcartes, Bernoulli, and Newton. It is on the laft that his attention is principally fixed. The fyftem of Le Sage is barely alluded to, (and fo incorrectly as to

make

make it doubtful whether it be what is really meant); and that of Bofcovich is not fo much as mentioned.

Concerning the fyftem of Defcartes, it was not neceffary to enter into much detail; and Mr Vince has very properly abftained from doing fo. The vortices of that ingenious theorist have long ceafed to afford fatisfaction even to the moft fuperficial reafoner. They are known now only in the hiftory of opinions, and, in that hiftory, will ever furnish a most inftructive chapter. The manner in which the fyftem fprung up at the dawn of science, flourished on the ruins of the school philofophy, and faded of itfelf in the brighter light of experiment and obfervation, is the best proof of the fuperior value of the inductive philofophy which 'Defcartes fo unwifely affected to defpife.

A very just remark made by Mr Vince on the fyftem of Defcartes, and on all others that depend on the fame principle, is, that the planets being carried in vortices round the fun, the quantity of matter in the fun will not affect the velocity of the vortex, or the bodies immersed in it, inafmuch as that velocity might be the fame, though there were no central body whatfoever. The quantity of matter in the fun, therefore, cannot enter at all as an element into the expreffion of the force by which the planet is impelled toward the fun. Therefore, as the fact is, that the quantity of matter in the central body does enter as a most material element into the expreffion of the gravitation of the planet, it is impoflible to afcribe that gravitation to the action of a vortex. This argument is perfectly conclufive. It was not to this, however, that the fyftem 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 fuppofe the vortex fo arranged, that it will explain one of thofe great facts in the planetary motions, known by the name of Kepler's Laws, it becomes quite inconfiftent with the reft.

The next fyftem that was imagined for explaining the law of gravitation, was that of an elastic ether, mentioned by Sir Ifaac Newton in the Queries at the end of his Optics, and proposed with fuch modesty and diffidence, as entitles it to great indulgence. It is the conjecture of the philofopher, who had demonstrated the existence of the law of gravitation, concerning the mechanism by which this univerfal tendency is produced; and feems to be thrown out with the view of preventing those who followed him from thinking that it was fufficient to fay that gravitation was an effential quality of matter, and that there was no occafion to trouble themselves about the cause of it. It was to ferve as a ftimulus to future inquiry, and as a caution against fuppofing that the fabric of phyfical aftronomy was complete. According

to

to it, the mutual tendency of bodies toward one another, arifes from the action of a fluid highly elaftic, diffused through all space, but more rare within bodies than without, and more rare at a fmaller diftance from them than at a greater. Bodies are propelled through this fluid from the denfer to the rarer parts, that is, from the parts where the elafticity is greater, to those where it is lefs. Thus, with refpect to the earth, the elafticity of the circumfufed ether being greater at a distance from that body than near it, other bodies would, by that greater elafticity, be urged toward the quarter where the elafticity is lefs, that is, toward the earth. The fame would hold of the fun and moon, and all the great bodies of the univerfe. This hypothefis, to which it must be confefled that many objections may be made, appears to have been fuggested to Newton by the phenomena of optics, which it is better calculated to folve than thofe of aftronomy. That a fubtle fluid exifted, and was diffufed through thofe fpaces from which air was exhaufted, appeared to him evident from many confiderations, and particularly from this, that a thermometer in vacuo will grow warm almoft as foon as a thermometer not in vacuo. Is not the heat, therefore,' faid he, of a warm room conveyed through the vacuum by the vibrations of a much fubtler medium than air, which, after the air was drawn out, remained in the vacuum?' Again, he fays, Doth not the refraction of light proceed from the different denfities of this ethereal medium in different places, the light receding always from the denfer parts of the medium towards the rarer? And is not the density thereof greater in free and open fpaces void of air and other grofs bodies, than within the pores of water, glafs, crystal, and other compact bodies? For when light paffes through glafs or cryftal, and, falling obliquely upon the further furface 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 weaknefs. Now, in applying this fluid to account for the gravitation of diftant bodies toward one another, he fuppofes, as before ftated, that its denfity, and, of course, its elafticity, increafes as you recede from the fun and other great bodies; that it is lefs within than at the furface; lefs there than at a fmall diftance from it, (as the phenomena of optics feemed to require); and that it goes on continually, though flowly, increafing. Though this increafe of denfity," he adds, may be exceeding flow at great diftances, yet if the elaftic force of the medium be exceeding great, it may fuffice to impel bodies from the denfer 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 hypothefis; and Mr Vince dwells particularly on one deduced from the impoffibility