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In the period of this fatellite I have employed the obfervation of the 19th Auguft, 1787, as, from other calculations, it feems the revolution is determined near enough to reach back fo far.

• The most diftant obfervations of the feventh fatellite, being compared together, fhew, that it makes one fidereal revolution in 22 hours, 40 minutes, and 46 feconds and by the fame data, which ferved to a certain-the dimension of the orbit of the fixth, we have the diftance of the feventh, from the center of Saturn, no more than 27366. It is incomparably fmailer than the fixth; and even in my forty-fect reflector, appears no bigger than a very fmall lucid point. I fce it, however, alfo very well in the twenty-feet reflector; to which the exquifite figure of the fpeculum not a little contributes. It muit nevertheless be remembered, that a fatellite once difcovered, is much ealier to be seen than it was before we were acquainted with its place.

The revolution of this fatellite is not nearly fo well afcertained as that of the former. The difficulty of having a number of obfervations is uncommonly great; for, on account of the finallnefs of its orbit, the fatellite lies generally before and behind the planet and its ring, or at least fo near them, that except in very fine weather, it cannot eafily be feen well enough to take its place with accuracy. On the other hand, the greatest clongations allow fo much latitude for miftaking its true fituation, that it will require a confiderable time to divide the errors that muft arife from imperfect eftimations.

The orbits of thefe two fatellites, as appears from many obfervations of them, are exactly in the plane of the ring, or at least deviate fo little from it, that the difference cannot be perceived. It is true, there is a poffibility that the line of their nodes may be in, or near, the prefent greatest elongations, in which cafe the orbits may have fome fmall inclination; but as I have repeatedly feen them run along the very minute arms of the ring, even then the deviation cannot amount to more than perhaps one or two degrees; if, on the contrary, the nodes fhould be fituated near the conjunction, this quantity would be fo confiderable, that it could not have efcaped my obfervation.'

Among the other obfervations on the planet Saturn, we find that the Doctor has constantly obferved belts upon the furface of Saturn, and generally in equatorial fituations, though now and then otherwife; from which it is inferred that Saturn has a confiderable atmosphere, and turns upon an axis which is perpendicular to the ring. This laft fact is afcertained by the prolate figure of Saturn, likewife, as it is determined by the Doctor's obfervations, that the diameter perpendicular to the ring is less than that which lies in its plane in the proportion of 11 to 10. On the 14th of September, 1789, the two diameters of Saturn, meafured with the twenty-feet reflector, and a good parallel wire micrometer proved to be by the means of four obfervations of the equatorial, and three of the polar diameter, the former 22".81, and the latter 20".61. The Doctor

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has

has drawn no inference with regard to the time of Saturn's rotation, though by a remarkable set of obfervations, in the month of June, 1780, a cloudy appearance of confiderable magnitude was obferved to move on the difk, fo as to denote a rotation in the fame direction as that of the other planets. And these obfervations, together with the proportions of the diameter, seem to authorize a conjecture that Saturn revolves on its axis in fomething lefs than half a day.

Art. 2. Aftronomical Obfervations on the Planets Venus and Mars, made with a View to determine the heliocentric Longitude of their Nodes, the annual Mction of the Nodes, and the greatest Inclination of their Orbits. By Thomas Bugge, F. R. S. Regius Profeffor of Aftronomy at Copenhagen, Member of the Academies of Stockholm, Copenhagen, Manheim and Dronheim, and Correfpondent of the Academy of Sciences at Paris. Thefe obfervations are made with a fix feet tranfit inftrument, and a fix feet mural quadrant. The prefent communication contains only the refults, which are tabulated, and compared with the tables of Dr. Halley and De Lalande. We can only obferve, therefore, that their utility for determining the objects mentioned in the title will be obvious to astronomers, and that it would be impracticable to attempt any abridgment of this paper.

Art. 3. An Account of fome luminous Arches. In a Letter from Mr. William Hey, F. R.S. to the Rev. Jofeph Priestley,

LL. D. F. R. S.

Art. 4. Extract of a Letter from F. J. H. Wollafton (dated Sydney College, Cambridge, Feb. 24, 1784) to the Rev. Francis Wellafton, L. L. B. F.R.S.

Art. 5. An Account of a luminous Arch. In a Letter from the Rev. Mr. B. Hutchinfon, to Sir Jofeph Banks, Bart. P. R.S. Art. 6. Extract of a Letter from J. Franklin, Efq. relative to a luminous Arch.

Art. 7. An Account of fome luminous Arches. In a Letter from Edward Pigot, Efq. to Sir Henry C. Englefield, Bart.

F. R. S.

The first four of thefe papers were read before the Society in the year 1786, and the committee of papers are doubtless entitled to the thanks of the public for bringing forward this mafs of facts on the prefent occafion, though as fincere wellwifhers to the profperity of the Royal Society, we cannot avoid regretting, that their communications are fo few for the present year, as that one third of their papers fhould be taken from the former communications; fo that if it were not for the voluminous account of the trigonometrical operation by major-general Roy, the new papers in the prefent book would not amount to one hundred pages. The Royal Society have repeatedly declared it as their invariable purpose, never to give

their opinion, as a body, upon any fubject either of nature or art that comes before them. The thanks of the Royal Society on all occafions are by themselves declared to be mere matter of civility; not of encouragement or approbation. What then, to the public at large, are the ufeful purposes this confeffedly illuftrious body is defigned to anfwer? The public, at large, knows them, as it does the other learned focieties of Europe, by no other effect than by the book they publish, upon the inestimable value of which their fame is grounded, though they have now for many years continued to publish an annual preface, in which they fem, as far, indeed, as their general rule will allow them, to be difpofed to give an opinion to the prejudice of the Tranfations. From the lift of great names which compofe the prefent Royal Society, a lift which may be put in competition with any of preceding times, and from the fcarcity of communications of late years, it feems as if an opinion had gained ground, that the Tranfactions are of little confequence to the fociety or the public. Can it be fuppofed that thefe great men have bid adieu to philofophical purfuits? can it be fuppofed that their refearches are not worth communicating or can they be imagined to be fo little awake to the true interefts of the fociety as to withhold them?-Nevertheless thefe communications do not appear. We fee an effort to increase the number of papers, by recurring to the archives for communications that former committees have laid afide. This at leaft fhews a confciouínefs of the evil, and we fincerely hope that it will be followed by exertions of a much more effectual

nature.

We shall not attempt to abridge the prefent fet of papers upon luminous arches, as they chiefly contain a relation of facts which are not applied to any general conclufions. Art. 8. Experiments on the Analysis of the heavy inflammable Air. By William Austin, M. D. Fellow of the College of Physi

cians.

Several claftic fluids, containing the light inflammable air, as the hepatic and alkaline airs, being decompofed by the electric spark, Dr. Auftin was induced to try it on the heavy inflammable air, which, agreeably to his expectation, suffered fuch an expanfion as detected the light inflammable air. Thus the heavy inflammable air was fometimes expanded to twice its original volume; and yet upon examining the air fo expanded, not a fixth part of the whole was found to have undergone a decompofition. From this partial decompofition a mixture was obtained of the two inflammable airs, together with phlogifticated air. It is true, indeed, that no method exifts by which one of thefe inflammable fubftances can be feparated from the other. But as it is known that dephlogisti cated air will combine with them, in certain proportions, either

mixed or separate, and forms with one, according to the Doctor's statement, fixed air, and with the other, water; it must follow, that by inflaming dephlogifticated air with a mixture of these two airs, and obferving the quantity of dephlogisticated air confumed above what is fufficient for the production of the fixed air, a conclufion may be drawn, that this excefs has combined with light inflammable air.

From a confiderable number of experiments of this kind, the Doctor endeavoured to approximate to the quantities of light inflammable air and phlogifticated air, which are feparated from heavy inflammable air by electricity, but found the method attended with too many difficulties to afford an accurate analytis. He therefore attempted to decompofe the heavy inflammable air by means of fulphur, which readily unites with the light inflammable air in a condenfed ftate, and with it forms hepatic air. He found that in whatever manner the heavy inflammable air was decompofed, an indication that volatile alkali is formed, took place.

The conclufions inferred by the Doctor are as follows.

1. That the heavy inflammable air contains the light inflammable air in great abundance.

I apprehend this light inflammable air was, before the application of the electrical spark, a conftituent part of the heavy inflammable air; becaufe, if it were contained in the heavier air not as a conftituent part, what fhould hinder its being burnt, when the heavy inflammable air is burnt? Can it be fuppofed, that the heavy inflammable air fhould contain the light infiammable air in circumftances of combuftion, and that the light inflammable air fhould efcape the fire? And if the lighter air be burnt, the fame quantity of dephlogisticated air would be neceflary to faturate it before, as after its being elec trified. But it is evident from the preceding experiments, that much more dephlogisticated air is necellary to faturate the air, after it has been expanded by the electrical fhock, than before.

2. That no fixed air is formed during the feparation of the lighter air from the heavy inflammable air.

Here it fhould be obferved, that if the conftitution of the heavy inflammable air depended on an union of the light inflammable and fixed airs, as fome have fuppofed, we should certainly discover the fixed air, when the other part was feparated from it. Or, fhould it be conjectured that the light inflammable air is feparated from water fufpended in the heavy inflammable air, in that cafe, would not fixed air be formed from the other constituent part of the water uniting with the heavy inflammable air in confequence of the repeated electrical fhocks?

3. That the electrical fhock feparated a fubftance from the heavy inflammable air, which has fome leading characters of an alkali.

When

When inflammable air is decompofed by fulphur, or when hepatic air is made from charcoal and fulphur, we have the fame appearance of an alkali. That this is the volatile alkali, is evident from its evaporation, when hepatic air is made from fulphur and charcoal.

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4. That the heavy inflammable air, through which the fpark has been repeatedly paffed, when burnt with any proportion of dephlogifticated air, does not produce fo much fixed air as the fame quantity of inflammable air not electrified.

Hence it is evident, that a part of the air is actually compofed by the fpark. Hence alfo we may infer, that the decompofed air is not refolved into light inflammable air and charcoal, of which fome chemifts have fuppofed it to consist, because the charcoa! would combine with dephlogisticated air after its feparation from light inflammable air, and we should not have fuch a defect of fixed air.

6. That the refidues, after inflaming the decompofed air, are generally greater than thofe from the air in its natural ftate, or than can be accounted for from the mixture of the heavy inflammable and dephlogisticated airs.

This affords a ftrong prefumption, that phlogisticated air is extricated from the decompofed heavy inflammable air in a feparate ftate, befides what enters into the volatile alkali, which is formed at the fame time. If light inflammable air only were difengaged during the decompofition, the refidues would certainly not be greater after inflammation, with a fufficient quantity of dephlogifticated air; on the contrary, if the inflammable air were increafed in proportion in the mixture, the combuftion would be more complete, and the refidues less.'

The whole of this paper is highly deferving the attention of chemical philofophers.

Art. 9. Some Account of the Strata and volcanic Appearances in the North of Ireland, and western Islands of Scotland.

Thefe letters contain much entertaining and inftructive matter, tending to explain the theory of the earth's furface; but of fuch a nature as cannot with any advantage be abridged. Art. 10. On the Height of the luminous Arch which was feen on February 23, 1784. By Henry Cavendish, Elq. F. R. S. A. S. After enumerating and arranging the general facts relative to this meteor, Mr. Cavendish deduces, that the height of the arch above the furface of the earth was hardly lefs than fiftytwo miles, and is not likely to have much exceeded feventyone miles. He conjectures that these luminous arches may confift of parallel ftreams of light, difpofed so as to form a long thin band, pretty broad in its upright direction, and ftretched out horizontally to a great length one way, but thin in the oppofite direction.

Art.

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