THESE experiments, which likewife relate to the preceding question, were made in a different order. The fcales were fixed on the furface of the earth, and after procuring an exact equilibrium between the oppofite weights in that fituation, thofe contained in one of the basons were let down to the depths of 114 and 190 yards, into a coal mine. Sometimes the undermoft weight preponderated, but more frequently the fuperior. The quantity, however, in either cafe, was fo small, that the au thor very properly concludes, from the refults both of his own and the many other experiments that have lately been made on the fubject, that they are infufficient to determine the queftion. In this opinion we readily concur with him; nor fhould we have taken fo much notice of the fubject, were not the question itself of great importance, and had it not likewife been fo very extenfively and warmly litigated, of late, among our neighbours on the continent. The experiments which have been produced in fupport of the theory of gravitation have indeed the merit of evincing the feeblenefs of this late attack upon it; but nothing further is or can be determined from them: nor does the Newtonian fyftem ftand in need of fuch feeble fupports. Non tali auxilio, nec defenjoribus iftis, &c. [Monthly Review.] Subftance of two curious Articles in the Second Part of the Sixty-fifth Volume of the Philofophical Tranfactions, being that for the Year 1775; viz. the Forty-eighth, be ΤΗ According to the Newtonian theory, an attractive power is not only exerted between thofe large maffes of matter which conftitute the fun and planets; but likewise between all comparatively fmaller bodies, and even between the fmalleft particles of which they are compofed. Agreeably to this hy pothefis, a heavy body, which ought to gravitate or tend toward the centre of the earth, in a direction perpendicular to its furface, fuppofing the faid furface to be perfectly even and fpherical, ought likewife, though in a lefs degree, to be attracted and tend towards a mountain placed on the earth's furface: fo that a plumbline, for inftance, of a quadrant, hanging in the neighbourhood of fuch fuch a mountain, ought to be drawn from a perpendicular fituation, in confequence of the attractive power of the quantity of matter of which it is compofed, acting in a direction different from that exerted by the whole mafs of matter in the earth, and with a proportionably inferior degree of force. attraction, draw the plumb-line two minutes out of the perpendicular" yet no attempt to afcertain this matter, by actual experiment, was made till about the year 1738; when the French academicians, particularly Meffrs. Bouguer and Condamine, who were fent to Peru to measure a degree under the equator, attempted to difcover the attractive power of Chimboraço, a mountain in the province of Quito. According to their obfervations, which were however made under circumstances by no means favourable to an accurate folution of fo nice and difficult a problem, the mountain Chimboraço exerted an attraction equal to eight feconds. Though this experiment was not perhaps fufficient to prove fatisfactorily. even the reality of an attraction, much lefs the precife quantity of it; yet it does not appear that any fteps had been fince taken to re, peat it. It will eafily be imagined,' fays the Aftronomer Royal, in the first of thefe papers, which was read before the Royal Society in the year 1772, that to find a fenfible attraction of any hill from undoubted experiment, would be a matter of no fmall curiofity, would greatly illuftrate the general theory of gravity, and would make the univerfal gravitation of matter palpable, if I may fo exprefs myfelf, to every perfon, and fit to convince thofe who will yield their affent to nothing but down right experiment. Nor would its ufes end here; as it would ferve to give us a better idea of the total mafs of the earth, and the proportional denfity of the matter near the furface compared with the mean denfity of the whole earth. The refult of fuch an uncommon experiment, which I fhould hope would prove fuccefsful, would doubtlefs do honour to the nation where it was made, and the fociety which executed it.' Though Sir Ifaac Newton had long ago hinted at an experiment of this kind; and had remarked that a mountain of an hemifpherical figure, three miles high and fix broad, would not, by its ex The Royal Society having, through the munificence of his Majelty, been enabled to undertake the execution of this delicate and important aftronomical periment; the aftronomer royal was chofen to conduct it. After various inquiries, the mountain Scheballien, ficuated nearly in the centre of Scotland, was pitched upon as the moft proper for the purpofe that could be found in this ifland. The obfervations were made by taking the meridian zenith diftances of different fixed ftars, near the zenith, by means of a zenith fector of ten feet radius; first on the fouth, By a very easy calculation it is found that fuch a mountain would attract the plumb-line 118" from the perpendicular. F 3 and and afterwards on the north fide of the hill, the greatest length of which extended in an east and weft direction. It is evident that if the mafs of matter in the hill exerted any fenfible attraction, it would cause the plumb-line of the fector, through which an obferver viewed a ftar in the meridian, to deviate from its perpendicular fituation, and would attract it contrary ways at the two fations, thereby doubling the effe&t. On the fouth fide the plummet would be drawn to the northward, by the attractive power of the hill placed to the northward of it and on the north fide, a contrary and equal deflection of the plumb-line would take place, in confequence of the attraction of the hill, now to the fouthward of it. The apparent zenith diftances of the stars would be affected contrary ways; thofe being increafed at the one ftation, which were diminifhed at the other: and the correfpondent quantities of the deflection of the plumb-line would give the obferver the fum of the two contrary attractions of the hill, acting on the plummet at the two ftations; the balf of which will, of courfe, indicate the attractive power of the hill. After defcribing his excellent aftronomical apparatus, and relating in detail the hiftory of a part of his various operations during his aftronomical campaign, which lafted about four months; the author gives the refult of them, from which it appears that the Jum of the two contrary attractions of the mountain Schehallien, in the two temporary obfervatories which were fucceflively fixed half way up the hill (where the effect * of its attraction would be greatest) was equal to 11". 6. From a rough computation, founded on the known law of gravitation; and on an affumption that the denfity of the hill was equal to the mean denfity of the earth; the author finds that the attraction of the hill fhould amount to about the double of this quantity. From thence he infers that the denfity of the hill is only about half the mean denfity of the earth. It does not appear however that the mountain Schehallien has ever been a volcano, or is hollow; as it is extremely folid and denfe, and feemingly compofed of an intire rock. Having by this curious and accurate experiment fatisfactorily afcertained the attraction of matter, and its quantity in the present cafe, the author proceeds to confider fome of the confequences which may be drawn from it, relative to ieveral of the most im- . portant queftions in natural philofophy. We fhall quote, with fome abridgments, what he observes on this fubject: 1. It appears from this experiment, that the mountain Schehallien exerts a fenfible attraction; therefore, from the rules of philofophifing, we are to conclude that every mountain, and indeed every particle of the earth, is endued with the fame property, in proportion to its quantity of matter. 2. The law of the variation of this force, in the inverse ratio of the fquares of the distance, as laid down by Sir Ifaac Newton, is alfo confirmed by this experiment. For, if the force of attraction of the hill had been only to that of the earth, as the matter in the hill to that of the earth, and had not been greatly increased by the near approach to its centre, the attraction thereof must have been wholly infenfible. But now, by only fuppofing the mean denfity of the earth to be double to that of the hill, which feems very probable from other confiderations, the attraction of the hill will be reconciled to the general law of the variation of attraction in the inverfe duplicate ratio of the distances, as deduced by Sir Ifaac Newton from the comparison of the motion of the heavenly bodies with the force of gravity at the furface of the earth; and the analogy of nature will be preserved. 3. We may now, therefore, be allowed to admit this law, and to acknowledge that the mean denfity of the earth is at least double of that at the furface, and confequently that the denfity of the internal parts of the earth is much greater than near the furface. Hence alfo, the whole quantity of matter in the earth will be at least as great again as if it had been all compofed of matter of the fame denfity with that at the furface; or will be about four or five times as great as if it were all compofed of water. This conclufion, he adds, is totally contrary to the hypothefis of fome naturalifts, who "fuppofe the earth to be only a great hollow fhell of matter; fupporting itfelf from the property of an arch, with an immenfe vacuity in the midst of it. But, were that the cafe, the attraction of mountains, and even fmaller inequalities in the earth's furface, would be very great, contrary to experiment, and would affect the measures of the degrees of the meridian much more than we find they do; and the variation of gravity, in different latitudes, in going from the equator to the poles, as found by pendulums would not be near fo regular as it has been found by experiment to be." 4. He obferves, laftly, that as mountains are, by these experiments, found capable of producing fenfible deflections of the plumblines of aftronomical inftruments; it becomes a matter of great importance in the menfuration of degrees in the meridian, either to chufe places where the irregular attractions of the elevated parts may be fmall; or, where, by their fituation, they may compenfate or counteract the effects of each other. [Monthly Review.] Parallel between the Old and New Worlds, with regard to Extent, Situation, Climate, Soil, Inbabitants, &c. from the Abbé Raynal's Philofophical and Political Hiftory of the Settlements and Trade of the Europeans in the Eaft and Weft-Indies. Tranflated by Mr. Juftamond. TT is furprifing that fo little In fhould have been known of the new world, for fo long a time after it was difcovered. Barbarous foldiers and rapacious merchants were not proper perfons to give us juft and clear notions of this hemifphere. It was the province of philofophy alone to avail itself of the informations fcattered in the accounts of voyages and miffionaries, in order to fee America, fuch as nature hath made it; and to find out its analogy to the reft of the globe. It is now pretty certain that the new continent has not half the extent of furface that the old has. F 4 At At the fame time, the form of both is fo fingularly alike, that we might eafily be inclined to draw confequences from this particular, if it were not always neceffary to be upon our guard against the fpirit of fyftem which often ftops us in our researches after truth, and hinders us from attaining it. The two continents feem to form as it were two broad tracts of land that begin from the arctic pole, and terminate at the tropic of Capricorn, divided on the eat and weft by the ocean that furrounds them. Whatever may be the ftructure of these two continents, and the equality or fymmetry of their form; it is plain their equilibrium does not depend upon their pofition. It is the inconftancy of the fea that conftitutes the folid "form of the earth. To fix the globe upon its bafis, it feemed neceffary to have an element which floating inceffantly round our planet, might by its weight counterbalance all other fubftances, and by its fluidity restore that equilibrium which the conflict of the other elements might have disturbed. Water, by its natural fluctuation and weight, is the most proper element to preferve the connection and balance of the feveral parts of the globe round its center. If our hemifphere has a very wide extent of continent to the north, a mass of water of equal weight at the oppofite part will certainly produce an equilibrium. If under the tropics we have a rich country covered with men and animals; under the fame latitude America will have a fea filled with fish. While forefts full of trees, bending with the largest fruits, quadrupeds of the greatest fize, the most populous nations, elephants and men are a load upon the furface of the earth, and feem to abforb all its fertility throughout the torrid zone; at both poles are found whales with innumerable multitudes of cod and herrings, clouds of infects, and all the infinite and prodigious tribes that inhabit the feas, as it were to fupport the axis of the earth, and prevent its inclining or deviating to either fide: if, indeed, elephants, whales, or men can be faid to have any weight on a globe, where all living creatures are but a tranfient modification of the earth that compofes it. In a word, the ocean rolls over this globe to fafhion it, in conformity to the general laws of gravity. Sometimes it covers a hemifphere, a pole or a zone, which at other times it leaves bare; but in general it feems to affect the equator, more especially as the cold of the poles in fome measure counteracts that fluidity which is effential to it, and from which it receives all its power of motion. It is chiefly between the tropics that the fea extends itfelf and is agitated, and that it undergoes the greatest change both in its regular and periodical motions, as well as in thofe violent agitations occafionally excited in it by tempeftuous winds. The attraction of the fun, and the fermentations occafioned by its continual heat in the torrid zone, muf have a very remarkable influence upon the ocean. The motion of the moon adds a new force to this influence, and the fea, to conform itself to this double impulfe, mult, it fhould feem, flow towards the equator. Nothing but the flatnefs of the globe at the poles, can poffibly account for that immenfe extent of water, that has hitherto concealed from us the lands near the |