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they will spread, as they obtain remained on the surface. In this pourishment by their adhering roots. mould he set cuttings of the plants

Having already mentioned Mr he wished to rear, and over them he Green, I shall here add another in- laid a cover of glass in a frame, which ftance of his ingenuity. As it takes fited so exactly that the water could some time to rear up flowering-shrubs not exhale. In this fruation, exposed or plants from the seed, he discovers to the warmth of the sun, the cuttings ed a more expeditious method. For made fresh shoots; and he observed, this purpose, he had a box made of that in proportion as the thoots such a size as he desired. The join. role upwards, freth roots grew ing of the several paris were dove. downwards. The cuttings were tailed into one another, and the join. kept in this state till he judged ings were covered with pitch, so that they had taken sufficient roots to as to become water-tight. He filled bear being transplanted. And in the box, perhaps, half full of rich this manner he was constantly supmould, and added water enough to plied with plenty of blowing plants. render it so moist as that the water

AGRICOLA

Account of the Discovery of a Sixth and Seventh Satellite of the Planet Saturn;

with Remarks on the Construction of its Ring, its Atmosphere, its Rotation 0% an Axis, and its spheroidical Figure, · By William Herschel, LL.D.

F. R. St. IN a short Poftfcript, added to my obje&t of almost every astronomer's

laft Paper on Nebulæ, I announ- curiosity, on account of the singular ced the discovery of a fixth satellite phænomena of its ring. But it will of Saturn, and mentioned, that I in- be seen presently, from the situation tended to communicate the particulars and size of the fatellites, that we of its orbit and situation to the Mem- could hardly expect to discover them bers of the Royal Society, at their till a telescope of the dimenfions and next meeting. I have now the hon- aperture of my forty-feet reflector our to present them, at the same time, should be constructed; and I need with an account of two satellites in- not observe how much we Members stead of one; and have called them of this Society must feel ourselves the sixth and seventh, though their obliged to our Royal Patron, for his fituation in the Saturnian system in- encouragement of the sciences, when titles them, very probably, to the we perceive that the discovery of these first and second place. This I have satellites is entirely owing to the libedone to the end that in future we ral fupport whereby our most benemay not be liable to mistake, in volent King has enabled his humble referring to former observations or astronomer to compleat the arduous tables, where the five known fatel- undertaking of constructing this inlites have been mamed according to Arument. . the order. they have hitherto been The planet Saturn is, perhaps, one fupposed to hold in the range of dif- of the most engaging objects that astrotance from the planet.

nomy offers to our view. . As such it It may appear' remarkable, that drew my attention so early as the year these fatellites should have remained 1774; when, on the 17th of March, so long unknown to us, when, for a with a si feet reflector, I saw its ring Century and an half past, the planet reduced to a very minute line. On the to which they belong has been the 3d of April, ia the same year, I found

the

the planet as it were, stripped of its a construction, by, way of explaining noble ornament, and dressed in the a phenomenon that does not absoluteplain fimplicity of Mars. I pass over the ly demand it. If one ring, of a following year, when with a 7 feet re- breadth so considerable as that of Sa. Sector, I saw the ring gradually open, turn, is justly to be esteemed the most and exhibit a dark broad line upon it, wonderfularch that, by the laws of gra. which I delineated from nature, on vity, can be held together, how imthe 20th of June 1788, by means of probable must it appear to suppose it a very good 10 feet reflector. subdivided into narrow Bips of rings,

It should be noticed, that the black which by this separation will be dedisk, or belt, upon the ring of Saturn, prived of a sufficient depth, and thus is not in the middle of its breadth; lose the only dimenfion which can nor is the ring subdivided by many keep them from falling upon the plasuch lines, as has been represented in net! It is however true, that as yet divers treatises of astronomy; but that we do not know of the rotation of the there is one lingle, dark, considerably ring, which may be of such a proper broad line, belt, or zone, upon the velocity as greatly to assist its strength; ring, at least upon the northern plane. and that, in the subdivisions, of course The southern one, which is lately the different velocities for each divicome to be exposed to the sun, will fion may be equally supposed to keep shortly be opened sufficiently to enable them up. If the southern plane should me to give also the situation of its prove to be very differently marked; belts, if it should have any

it will at once remove every furmise From my observations it appears, of such a division; but if it should of. that the zone on the northern plane fer us the same appearance of a dark of the ring is not, like the belts of zone, in the same fituation, and of Jupiter or those of Saturn, subject to an equal breadth with the one I have variations of colour and figure; but is observed on the northern lide, I would most probably owing to some perma- ftill remark, that, since a most effecbent construction of the surface of the tual way to verify the duplicity of the ring itself. That, however, for in- ring is within our reach, it will be stance, this black belt cannot be the the best way to suspend our judge shadow of a chain of mountains, may ment till that can be put to the trial. be gatisered from its being visible all The method I allude to is an occultaround the ring; for at the ends of tion of some considerable star by Sathe ansæ there could be no shades vi- turn, when, if the ring be divided, it fible, on account of the direction of will be seen between the openings, as the lun's illumination, which would well as between the ring and Saturn. be in the line of the chain ; and the With regard to the nature of the saine argument will hold good against ring, we may certainly affirm, that it fu pored caverns or concavities. It is no less folid and substantial than is moreover pretty evident, that this the planet itself. The same reasons da: K zone is contained between two which prove to us the folidity of the concentric circles, as all the pheno. one will be full as valid when applied mena answer to the projection of such to the other. Thus we see the shadow a zone.

of the body of Saturn upon the ring, As to the surmise, which might according to the opposite situation of occur to us, of a division of the ring, the sun. If we deduce the quantity or rather of two rings, one about the of matter contained in the body, from other, with the distance of an open the power whereby the fatellites are Space between them, it does not ap- kept in their orbits, and the time of pear eligible to venture on fo artifcial their revolution, it mua be remem

bereds bered, that the ring is included in the a manner that they served as excelresult. It is also in a very particular lent micrometers to estimate its thickmanner evident, that the ring exerts nels by. It may be prøper to mention a considerable force upon these revol. a few instance, especially as they will ving bodies, since we find them strong- serve to solve some phenomena that ly affected with many irregularities in have been remarked by other aftrotheir motions, which we cannot pro- nomers, without having been account. perly ascribe to any other cause than ed for in any manner that could be ada the quantity of matter contained in mitted, confiften:ly with other known the ring; at least we ought to allow facts. July 18. 1789, at 19 h. 41' it a proper share in the effect, as we 9", Gdereal time, the first fatillite do not deny but that the considerable seemed to hang upon the followiog equatorial elevation of Saturn, which arm, declining a little towards the I fall establish hereafter, must also north, and I saw it gadually advance join in it.

upon it towards the body of Saturn; The light of the ring of Saturn is but the ring was not so thick as the generally brighter than that of the lucid point. July 23. at 19 h. 41' 8", planet : for instance, April 19, 1777, the second satellite was a very little I saw the southern part of the ring, preceding the ring; but the ring apwhich passed before the body, very peared to be less than half the thickplainly brighter than the disk of Sa- ness of the satellite. July 27. at 20 h. turn, on which it was projected ; and 15' 12", the second satellite was about on the 271h of the same month, I the middle, upon the following arm found, that with a power of 410, my of the ring, and towards the fouth; seven-feet reflector had hardly light and the sixth satellite on the farther enough for Saturn, when the ring was end, towards the north ; but the arm notwithstanding sufficiently bright. was thinner than either of them. AuAgain, the vith of March 1780, I guít 29. at 22 h. 12' 25", the third tried the powers of 222, 332, and satellite was upon the ring, ocar the 449, successively, and found the light end of the preceding arm; ard my reof Saturn less intense than that of the mark at the time when I saw it was, ring; the colour of the body, with that the arm seemed not to be the the high powers turning to a kind of fourth, at least oot the third part of yellow, while that of ihe ring still re. the diameter of the satellite, which, mained white. The same result bap- in the situation it was, I took to be pened on June 25, 1781, with the less than one single second in diamepower 460,

ter. At the same time I also saw the I come now to one of the most re- seventh satellite, at a little distance markable properties in the construc- following the third, in the shape of tion of the ring, which is its extreme a bead upon a thread, projecting on thinness. The fituation of Saturn, for both sides of the same arm : hence we some months past, has been particu- are sure, that the arm also appeared lazły favourable for an investigation of thinner than the seventh satellite, which this circumstance; and my experi- is confiderably smaller than the fixih, ments have been so complete, that which again is a little less than the there can remain no doubt on this first fatellite. August 31. at 20 h. head.

48' 26", the preceding arm was londWhen we were nearly in the plane ed about the middle by the third saof the ring, I have repeatedly seen the tellite. Oétuber is.oh. 43'44", first, the second, and the third satel. I saw the sixth satellite, without oblites, pay, even the 6th and sevenih, fiuction, about the middle of the prepass before and behind the ring in such ceding arm, though the ring was but

barely

barely visible with my forty-feet re. by the rays of the fun : and that this Hector, even while the planet was in is plainly the cafe, we may conclude the meridian; however, we were then from its being visible in my telescopes a little inclined to the plane of the during the time when others of less ring, and the third satellite, when it light had loft it, and when evidently came near its conjunction with the we were turned towards the uneolightfirit, was so situated, that it must have ened side, so that we mus either see partly covered the first a few minutes the rounding part of the enlightened after the time I luft it behind my 'edge, or else the reflection of the light house. In all these observations the of Saturn upon the fide of the dark ring did not in the least interfere with 'ened ring, as we see the refleted light my view of the satellites. October 16. of the earth on the dark part of the

I followed the fixth and seventh satel. new moon. I will, however, not de. Sites up to the very disk of the planet; cide which of the two may be the and the ring, which was extremely cafe; especially as there are other very faint, opposed no manner of obstruc- Arong reasons to induce us to thipk, tion to iny seeing them gradually ap- that the edge of the ring is of such a proach the disk, where the seventh nature as not to reflect much light. vanished at 21 h. 36' 44", and the I cannot leave this subject without fixth at 22 b. 36' 44".

mentioning both my own former furI might bring many other instan. mises, and those of several other aftroces, if the above were not quite suf. nomers, of a fupposed roughness in the ficient for the purpose. There is, surface of the ring, or inequality in however, some considerable suspicion, the planes and inclinations of its fa: that, by a refraction through some ve- fides. They arose from seeing lumi. ry rare atmosphere on the two planes nous parts on its extent, which were of the ring, the satellites might be supposed to be projecting points, like lifted up and depressed, so as to be the moon's mountains ; or from see come vilible on both fides of the ring, ing one arm brighter or longer than even though the ring should be equal another; or even from seeing one art in thickness to the diameter of the when the other was invisible. I was, {mallest fatellite, which may amount in the beginning of this season, into a thousand miles. As for the ar- clined to the fame opinion, till one of gument of its incredible thinness, these supposed luminous poiots was which some astronomers have brought kind enough to venture of the edge from the thort time of its being invi. of the ring, and appeared in the Shape Gble, when the earth passes through of a satellite. Now, as I had collec. its plane, we cannot set nuch value ted crery inequality of this fort, it upon them; for they must hate fupe was easy enough for me afterwards to poied the edge of the ring, as they calculate all such furmises by the have also represented it in their f. known periodical time of the fir, fé. gures, to be square; but there is the cond, third, fixth, and feventh latek greatest reason to suppose it either lites; and I have always found that ipherical or fphoroidical, in which cafe such appearances were owing to some evidently the ring cannot disapp, ar för of these fatellites which were either any long time. Nay, I may venture before or behind the ring. The 20th to fixy, that the ring cannot poífibly of Ostuber, for inftance, at 22.6. disappear on account of its thinne's; 35' 46", I saw four of Sarorn's fatelSince, either from the edge or the lites all in one row, and at almost a fies, even if it were square on the equal dittance from each other, og corners, it must always expose to our the following fide; and yet the fork sght iome part which is illuminated fatellite, which was the fartheft of them all, was only about half way to- Saturn for a future opportunity. Be wards its greateft elongation from the fides, not having any tables of the body of Saturn. How easily, with satellites, I could not confidently say, an inferior telescope, this might have whether the fifih faceliite was not one been taken for one of the arms of Sa- of the five which I perceived in moturn, I leave those to guess who know tion that night, though afterwards Į what a degree of accuracy it must found, that the real fifth had also been require to distinguish objects that in view, and was marked down as a are so minute, and at the same time ftar, by the lester b, in a figure I de. fo faint, on account of their nearness lineated of Saturn and its fatellites to the duk of the planet. Upon the that evening whole, therefore, I cannot say, that In the year 1788, very little could I had any one instance that could in- be done towards a discovery, as my duce me to believe the ring was not twenty-feet speculum was so much tarof an uniform thickness ; that is, e- nished by zenith sweeps, in which it qually thick at equal distances from had been more than usually exposed the centre, and of an equal diameter to falling dues, that I could hardly throughout the whole of its construc- see the Georgian satellites. In hopes tion. The idea of protuberant points of great success with my forty-feet upon the ring of Saturn, indeed, is of speculum, I deferred the attack upon ittelf sufficient to render the opinion Saiurn till that should be finished; of their existence inadmissible, when and having taken an early opportuniwe consider the enormous size such ty of directing it to Saturn, the very points ought to be of, for us to see them first monacnt I faw the planet, which at the distance we are from the planet. was the 28th of last Auguft, I was

From these suppoled luminous prelented with a view of lix of its sapoints I am, by imperceptibie steps, iellites, in such a situation, and so brought to the dilcovery of two bright, as rendered it imposible to satellites of Saturn, which had efca- mistake them, or not to see them. ped unnoticed, on account of their The retrograde motion of Saturn aTittle distance from the planet, and mounted to nearly 45 minutes per day, faininess; which latter is partly to which made it very easy to ascertain be ascribed to their smallness, and whether the liars I took to be satelparıly to being so near the light of lites really were fo; and, in about the ring and disk of Saturo. Strong two hours and an half, I had the pleafufpicions of the existence of a fixth fure of finding, that the planet had Satellite I have long entertained; and, visibly carried them all away from if I had been more at leilure two their places. I continued my obser. years ago, when the discovery of the vations constantly, whenever the weatwo Georgian satellites took me as it ther would permit; and the great light were off the scent, I should certainly of the forty-feet speculum was now of have been able to announce its exift- so much use, that I also, on the 17th euce as early as the 19th of August of September, detected the seventh 1787, when, at 22 h. 18'56", I saw, farellite, when it was at its greatest and marked it down as being probably, preceding elongation. a fixth satellite, which was then about As soon as I had observations 12 degrees palt its greatest preceding enough to make tables of the motion elongation. But, as I observed be- of these new fatellites, I calculated fore, not having time to give my their place backwards, and soon found thoughts to the subject, I reserved a that many suspicions of these fatellites, full investigation of the number of fa. in the shape of protuberant points on "Hellites, and the nature of the ring of the arms, were confirmed, and served

VI VOL. XII. N° 71.

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