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to correct the tables, fo as to render lefs be remembered, that a satellite them more perfect.

once discovered is much easier to be By comparing together many ob- feen than it was before we were 2c fervations of the fixth satellite, I find, quainted with its place. that it complerts a sidere al revolution. The revolution of this farellite is about Saturn in one day, 8 hours, not nearly to well ascertained as that 53'9". And if we suppole, with M. of the former. The difficulty of hade la Lande, that the fourth is at the ring a number of obfervations is upmean distance of 3' from the centre conamonly great ; for, on account of of Saturn, and performs one revolu. the smallness o: its orbit, the satellite tion in 15 d. 22 h, 34' 38", we find lies generally before and behind the the distance of the fixth, by Kepler's planet and its ring, or at least to near law, to be 35",058. lis light is con. then, that, except in very fine weather, fiderably strong, but not equal to that it cannot eatily be seen well toough of the first satellite ; for, on the 20th to take its place with accuracy. On of October, at 19 h. 59' 46", the first, the other hand, the greatest elonganotwithstanding it was nearer the pla- tions allow so much: lavtude for mi. ner than the lisch, was still visibly taking its true situation, that it will brighter than the liter. It would, require a considerable time to divide however, be worth while to try whe- the errors that must arise from ime ther a good achroma ic telescope, of perfect estimations. a large aperture, might not poflibly The orbits of these two satellites, thew it at the time of its greatest di- as appears from many obiervations of Atance from the planet, and when no them, are exa&tly in the plane of the other satellite is near; that is, pro- ting, or at le-t deviate so little from vided it will shew the other five fatul it, that the difference cannot be per: Jites with great ease, as otherwise ceived. It is true, there is a pothbi: there will be no reason to expect it lity that the line of their nodes may should shew the sixth

be in, or near, the prelent greatest In the period of his fatellite I have clongation, in which cale the orbiçs employed the observation of the 19th may have some small inclination; but of August 1787, as, from other cal. as I have repeatedly seen the run cularions, it seems the revolution is along the very minute arms of the detern in d near enough to reach ring, even then the deviation cannot back so far.

anigunt to more than perhaps one or The most diftant observations of the tuo degrees; if, on the contrary, the sevenih farellițe, be. ng compared to- podes should be fituared near the congether, thew, that it makes one Gde junction, this quantity would be la real revolution in 22 hours, 40 mi. considerable that it could not have nutes, and 46 seconds : and, by the escaped my observation. same data which served to ascertain From the ring and ficellites of Sa. the dimension of the orbit of the sixib, turn we now rurn our thoughıs to the we have the distance of the seventh, planet, its belis, and iis figuie. from the center of Saturn, no more April 9, 1775, I observed a Dorthern than 27''366. It is incomparably belt in Saturn, which was a little fmaller than the fixth; and, even in inclined to the line of the ring my forty-feet rector, appears no big. May 1, 1776. There was another ger than a very finali lucid point. I belt, inclined about 15 degrees to fee it, however, also very well in the the same line, but it was more to the ewenty-fert reflector ; to which the fouth, and on the following Gde exquifire figure of the speculum not a came up to the place in which the little contribuces. It must neverthe ring crosses the body.

"July

July 13, 1976. The belt was again ed ; with 200, 250, 300, 400,

depressed towards the north, almost faint appearances of a second and touching the line where the ring of a third belt. pafled behind the body.

Aug. 27. The belts less inclined. . April 8, 1777. There were two fine Sept. 2. A darkish belt, but very lite

belts, both a little inclined to the le inclined ; and a fine white belt, ring.

close to the ring. June 20, 1778. There were two belts 5. The belt a little inclined. - parallel to the ring ; but the nor -6. The belt not inclined.

thera one had some faint, cloudy - 8. The bright belt close to the appearance, towards the preceding ring, and two dark equatorial belts. or wettern Gde.

• It will not be necessary to continue May 11, 1779. Two equatorial belts. the account of these belis up to the

13,- A bright belt over a present time ; but I have constantly a dark one,

observed them, and found them genes 22,- . One dark, and one rally in equatorial situations, though, very faint white belt.

now and then they were otherwise. . 23, a A dark belt, and a We may draw two conclusions from ! pretty bright white one. . what has been reported. The first, Jan. 21, 1780. Two belis; the most which relates to the changes in the north ciouded.

appearance of the belts, is, that Sa,' - 22, Faint belts.

Turn has probably a very cooliderables May 17, A dark, equatorial atmosphere, in which these changes belt."

take place; just as the alterations in . 23, A strong, equatorial the belts of Jupiter have been shewn, belt,

with great probability, to be in his June 19, at 10 h. 15'. With a new, atmosphere. This has alio been con

excellent seven-feet speculum, I see firmed by other observacions: thus, two belts, and a cloudy appearance, in occultations of Saturn's satellites, which is not come up to the mid- I have found them to hang to the dle; but, as it is a large figure, dilk a long while before they would fone part of it is already past the vanish. And though we ought to

center (this is, provided Saturn make some allowance for the en · turns upon its axis the same way as croachment of light, whereby a fatel, Jupiter does).

lite is seen to reach up to the disle 1 June 20, 1780. 10 h. 10'. The same sooner than it actually does, yet,

figure is on the dilk, but seems to without a considerable refraction, if be more central than it was yestere could hardly be kept so long in view day.

after the apparent contact. The time 21, yh. 25'. The same iwo belts, of hanging opon the disk, in the leveort a strong, dark spot, near the mar- satellite, kas actually amounted 19 gin of the dilk,

twenty minutes. Now, as its quick. 10 h. 1'. The spot not so remarkable motion during that interval carries it ; as it was at 9 h. 25'.

through an arch of near six degrees, we - 26, Small twenty-feet telescope; find, that this would dmuote a refrac

an equatorial belt, and another less tion of about two teconds, provided marked.

the encroaching of light had no share 29. I'wo dark equatorial belts. in the effect. By an observation of April 19. Two belts.

the sixth satellite, the refraction of August 23. Two belts, a little de Saturn's atmosphere amounts to neaf

clining from the equatorial position. Jy the same quantity; for this fatel20. A broad belt much inclin. lite remained about 14 of 15 mioutes U uz

longer

longer in view than it should have and the Earth, is flattened at the done; and as it moves about 2.'s de- Poles; and therefore ought to be fupi grees in that time, and its orbit is posed to turn on its axis. larger than that of the seventh, the difference is inconsiderable. It is not July 22, 1776. I thought Sacarn wa my present intention to enter into a not exactly round. consideration of the amount of these May 31, 1781. It appears as if the refractions, otherwise we might per body of Saturn was at lealt as much haus find data enough to subject them flattened as that of Jupiter ; but as to some calculation. But what has the ring interferes, this may be been said will suffice to thew, that very better ascertaincd eight years hcoce. probably Saturn has an atmosphere of August 18, 1787. The body of Sa. a confiderable denlity.

turn is of unequal diameters, the The next inference we may draw equatorial one being the longeft.. from the appearance of the belts on Sept. 14, 1789, 23 h. 36' 32". HaSatorn is, that this planet turns upon ving reserved the examination of an axis which is perpendicular to the the two diameters of Saturn to the ring. The arrangement of the belts, present as the most favourable during the course of fourteen years

time, I measured them with my that I have observed them, has als twenty-feet reflector, and a good ways followed the direction of the parallel wire micrometer. ring, which is what I have called being equatorial. Thus, as the ring Equatorial diameter, ist mea. " opened, the belts began to advance sure,

21,94 towards the south ; and to shew an

2d 23,11 incurvature answering to the projec

3d - 21,73 tion of an equatorial line, or to a pa

4ih • 22,85 rallel of the same. When the ring cloled up, they returned towards the

Mean 22,81 north; and are now, 'while the ring paffes over the center, exactly ranging Polar diameter, ift measure, 20,57 with the shadow of it on the body;

2d · - 20,10 generally one on each side, with a

3d . 21,16 white belt close to it. When I say, that the belts have always been equatorial,

Mean 20,61 I pass over trifling exceptions, which certainly were owing to local causes. By this it appears that Saturn is The step from équatorial belts to a considerably flattened at the poles, rotation on an axis is fo easy, and, in And as the greatest measures were the case of Jupiter, so well ascertain taken in the line of the ring and of the ed, that I mall nor hefitate to take the belts, we are affured that the axis of same consequence for granted here. the planer is perpendicular to the plane But, if there could remain a doubt, of the ring; and that the equatorial the observations of June 19, 20, and diameter is to the polar one Dearly as 21, 1780, where the fame spot was 11 to 10. seen in three different lituations, would We may also infer the real diame. remove it completely.

ter of Saturn from these measures, There is another argument, of equal which are perhaps more to be depende validity with the former, which now ed upon than any that have hitherto I shall bring on. Iis founded upon been given. But as in my journal I the following ob'ervations, and will have measures that were repeatedly thew that Saturn, like Jupitcr, Mars, taken these ten years past, not one

wil. .

of the diameter of Saturn, but of the great use in ascertaining the quantity ring, and its opening, whereby is in- of matter contained in the planet, I clination may be known ; as well as reserve a full inveftigation of rhcio of the distance of the fourth, and fifth, things for another dpportunity. and other fatellites, which will be of

Some Account of the Strata and Volcanic' Appearances in the Wefern

Islands of Scotland. In a Letter from Abraham Mills, Esq; to John Lloyd,
Ésq; F. R. S*.
THE volcanic country, which low spots, where the soil is fandy,

we explored together in the and produces not only grass, but illand of Mull, having hitherto re- likewise corn and potatoes. The mained undefcribed by any traveller, whole extent of the island is three Į shall now beg leave to remind you miles in length N. E. and S. W. and of what we saw there, and in our one mile in breadth ; and it entirely voyage to Staffa.

con Gits of alternate barren crags and Sailing from Freeport, in the island little fertile vales. of llay, at ten o'clock at night, of Having engaged a boat with four Wednesday, July 2, 1788, we pal- rowers, we went from Icolmkilt sed Colonsay, without being able to through the Bull Sound, which runs diftinguish the substance of its shores; between Nun's Iland and the island but entering the sound of lona, we saw of Mull; on both sides the cliffs are that the rude coast of Mull, and the of red granite, ragged and broken, less elevated shore of Iona, was com- without any regular beds or filuress posed of red granite. Ar the landing and having no particular range or place in Iona is laminated borostone; inclination. Hence we steered for and a quarter of a mile north from the Ardlun Head, which forms the S. W. ruins of the Cathedral is a ve'n of point of Loch Leven. When we coarse red granite, two feet wide, approached the Head, we stopped standing nearly vertical, and ranging the rowers, and sat fome time con. with the hornitone E. N. E. and W. templating the wonderful arrangea S. W. on the surface are tumblers of ment of the basalt columns; and red granite, and some few of lava. as we again rowed along Shore About a mile N. W. from the Ca- to the eastward, had a fine view thedral, and near the shore, is a vein, of the various fituatiuns into two feet wide, containing feldspath which the columns were thrown. and white mica, ranging E. and W. The coast being every where steep, between granite sides. Many of the it was some time before we could rocks are tinged with iron, and there find a convenient place to land , is some bog iron ore in the moffes. but having at last gor on snore, we In the S. W. part of the island, is a walked to the extreme point or head : body of white marble, veined with here, struck with the errors of our pale green. At the Cove, where it maps, which placed the islands in is said St Columb landed, the cliffs right very differently from their true are of red granite, and the shore is situations, I took the following bear covered with great variety of pebbles ings by the compass. of serpentine, basaltes, granite, quartz, The N. E. point of Iona N.W. by W. and other substances. The N. W. The Dutchman's Cape N.N.W. part of the Inand is very rocky, Cairoborough N. by W.-Scaffa afording little pasture, except in some from N. to N. W. diftant, by es

timation - rcm the Same.

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timation, about three leagues. Rhu not so close as those of the Giant's -1 Thalve, the northernmost extreme Causeway; but, like those, their topsa of Mull, N. by E.-Inch Kenneth where exposed, are either concave or N.E.N.- The point of Ben Vaw- convex. ruch, on the north side of Loch At the extremity of the glea is an Leven, N. E. distant, by estimation, insulated rock, supported by basalt three miles.—The range of Loch pillars, which are somewhat curved Leven E. by S. and W. by N.. and inclined. Incumbent on these

About a quarter of a mile from the are other pillars, lying nearly horis spot wbere the bearings were taken, zontal, and having a rude face of lava is a deep glen, running N.N.E. to to the westward. At high-water this the sea. It is about thirty yards in rock is inacceslible without a boat; length, and twenty in breadth. The but at low-Water it may be easily got ftrata are disposed in the follow- at, by stepping from one tumbler to ing extraordinary manner :--The up- another; and on the north side it is permost is ten yards of lava, with ho- not difficult to climb to the top. Tho rizontal divisions and verticle joints, bottom of the glen is covered with taking the form of rude pillars. Un- large tumblers of lava the whole way der this is an horizontal bed of a per- down to the rock, and presents the fectly vitrified substance, which appears rudest scene imaginable. to have been a shale, and is from one Opposite Ardlun Head, on the to two inches in thickness. Beneath north side of Loch Leven, is Ben this, is about three yards of a hlice- Vawruch, an high promontory, whose ous gravelly concrete ; below which strata are in horizontal beds; and the are horizontal beds of indurated marl, bill being of a circular figure, gives it of various thicknesses, from fix to the appearance of several terraces, with twelve inches. The whole of these a kind of castle or cairn on the top. beds, taken together, are about four T he columnar pillars at drdlun yards, and there is a large fiffure in are more or less regular for an extent them, on the west side of the glen. of near a mile and an half; and all Lastly, are ten yards of rude lava, the projecting points of Loch Leven, containing fpects of quartz and mica as far as the eye could reach, appear. unaltered, pieces apparently of gra- ed to be composed of lava nite, and somenodules of calcined chert. Amongst the rude lava, which The whole is incumbent on regular ba- forms the bafis below high water mark, sale pillars, of various dimenfions, are nodules of crystal and agate, ador from eighteen to fix inches diameter, hering in small lumps to the rocks varying in the number of their fides, but, being blackened by the washing some having five, fome fix and others of the sea, are not to be discovered feven fides. They are also as vari- without a very nice search. Our ously disposed; those on the western boarmen informed us, that higher up extremity of the glen being straight, the Loch there is a bed of coal. This and lying horizontally ; whilft of those we withed to see ; but, as they also on the east side some are bare, and told us, that the weather, which bad standing perpendicularly; and others, for some day, palt beeo very tempelwhich are furmounted by the rude tuous, was now favourable for landing lava, are inclined and curved, as if on Staffa, we determined to avail they had taken that form in cooling ourselves of the opportunity, and got from the pressure of the incumbent into the boat, highly pleased with weight. Many of the pillars are what we had seen; and for which very full of bladder-holes the arti. pleafure we were indebted to the hint culations of the joints are close, though in Dr Johnson's Tour to the Hebrides.

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