ASTRONOMY. 3 s 7 
June 19, 1691, faw the oval figure of Saturn’s fliadow up¬ 
on liis ring. Mr. Bugge determines (Philol. Tranf. 1787, 
p. 42) the heliocentric longitude ot Saturn’s defcending 
"node to be 9!. 21 0 . 5'. 8|". and that the planet was in 
that node Auguft 21, 1784, at iSh. io'. 10". time at Co¬ 
penhagen. 
The annual period of Saturn about the Sun, is io759d. 
7h. or almoft thirty years; and his diameter is about 67000 
miles, or near 8£ times the diameter of the Earth ; alfo 
his diftance is about o£ times that of the Earth. Hence 
fome have concluded’ that his light and heat are entirely 
unfit for rational inhabitants. But that their light is not 
fo weak as we imagine is evident from their brightnefs in 
the night-time. Befides, allowing the Sun’s light to be 
45000 times as ftrong, with refpett to: us, as the light of 
the Moon when full, the Sun will afford 500 times as much 
light to Saturn as the full Moon does to us, and 1600 times 
as much to Jupiter. So that thefe two planets, even with¬ 
out any Moon, would be much more enlightened than we 
at firft imagine. Their heat, fo fur as it depends on the 
force of the Sun’s rays, is certainly much lefs than ours ; 
to which no doubt the bodies of their inhabitants are as 
well adapted as ours are to the feafons we enjoy. And if 
it be conlidered that Jupiter never lias any winter, even at 
his poles, which probably is alfo the cafe with Saturn, the 
cold cannot be fo intenfe on thefe two planets as is gene¬ 
rally imagined. To this may be added, that there may 
be fbmethrng in the nature of their mould warmer than in 
that of our Earth ; and we find that all our heat does not 
depend on the rays of the Sun ; for, if it did, we (hould 
always have the fame months equally hot or cold at their 
annual return, which is very far from being the cafe. 
Of the Ring of Saturn. 
The ring of Saturn is a broad circular arch, encompaffi- 
ing the body of that planet, without touching it, fome- 
what fimilar to the wooden horizon of an artificial globe ; 
only that the interior fpace occupied by the planet is very 
confiderable. Galileo was the firft perfon who difcovered 
it. The planet appeared to him like a large globe between 
two fmall ones. In the year 1610 lie announced this dif- 
covery. He continued his obfervations till 1612, when he 
was furprized to find only the middle globe; but fome time 
after he difcovered the globes on each fide, which, in pro- 
eefsof time, appeared to change their form ; iometimes ap¬ 
pearing round,foinetimesoblong like an acorn, fometimesfe- 
micircular, then with horns towards the globe in the middle, 
and growing by degrees fo long and wideas toencompafsit,as 
it were, with an oval ring. Upon this Huygens fet about im¬ 
proving the art of grinding objedt-glaffes ; and made tele¬ 
scopes which magnified two or three times more than any 
which had been made before, with which he difcovered 
very dearly the ring of Saturn appearing like anfae han¬ 
dles, arifing from the body of the planet ina right line; and, 
having observed this phenomenon for fome time, he pub- 
liftied the difcovery in 1656. He made the fpace between 
the globe and the ring equal to, or rather bigger than, the 
breadth of the ring ; and the greateft diameter of the ring 
to that of the globe as 9 to 4. But Mr. Pound, with a 
micrometer applied to Huygens’s telefcope of 123 feet 
long, more corredly determined the ratio to be as 7 to 3. 
Mr. Whifton, in his Memoirs of the Life of Dr. Clark, 
relates, that the doctor’s father once faw a fixed ftar be¬ 
tween the ring and the body of Saturn. In the year 1675, 
M. Caffini faw the ring, and obferved upon it a dark el¬ 
liptical line dividing it as it were into two rings, the inner 
of which appeared brighter than the outer. He alfo ob¬ 
served a dark belt upon the planet, parallel to the major 
axis of the ring. Mr. Hadley obferved that the outer 
part of the ring feemed narrower than the inner part; and 
that the dark line was fainter towards its upper edge ; he 
alfo faw two belts, and obferved the ftiadow of the ring 
upon Saturn. In Odober 1714, when the plane of the 
ring very nearly palled through the Earth, and was ap¬ 
proaching to it, M. Maraldi obferved, that, while the 
arms of the ring were decreafing both in length and 
breadth, the eaftern arm appeared a little larger than the 
other for three or four nights ; and yet it vanifhed firft, 
for, after two nights interruption by clouds, he faw the 
weftern arm alone. This inequality of the ring made him 
fufped that it was not bounded by exadly parallel planes, 
and that it turned about its axis. But the bed deferiptiorx 
of this Singular phenomenon is that given by Dr. Herlchel 
in the Philof. Tranf. for 1790, who by his extraordinary 
telefcopes has difcovered many circumftances which had 
efcaped all other obfervers. We Shall here give the lub- 
ftance of his account. Fig. 1, in the Aftronomical-Plate 
V. is a view of Saturn and its ring, as they appeared to 
him on June 20, 1778. 
The black diik, or belt, upon the ring of Saturn is not 
in the middle of its breadth ; nor is the ring fubdivided’ 
by many fuch lines, as Iras been reprefented by fome af- 
tronomers ; but there is one Tingle dark conliderably broad 
line, belt, or zone, as in the figure, which he has conftantly 
found’ on the north fide of the ring. As this dark belt is 
Aibjedr to no change whatever, it is probably owing to fome 
permanent conftrudion of the furface of the ring. This- 
conftrudion cannot be owing to the ftiadow of a chain of 
mountains, Since it is vifible all round on the ring ; for at 
the ends of the ring there could be no fhade ; and the 
lame argument will hold a-gainfranv fuppofed caverns. It 
is moreover pretty evident, that this dark zone is con¬ 
tained between two concentric circles, as all the pheno¬ 
mena a-nfwer to the projection of fuch a zone. The na¬ 
ture of the ring is unovibtedly no lefs foiid than-thepianet 
i-tfelf; and it is obferved to cult a ftrong ftiadow upon the 
planet. The light of the ring is alio generally brighter 
than that of the planet; for the ring appears Sufficiently 
bright, when the telefcope affords Scarcely light-enough 
for Saturn. Dr. Herfchel from a feries of obfervations 
upon-luminous points of the ring, alfo difcovered that it 
has a rotation about its axis, the time of which is loh. 32'. 
i5’4". The Sun Urines almoft fifteen of our years toge¬ 
ther on one fide of Saturn’s ring without'ferting, and as 
long on the other in its turn ; fo that the ring is vifible to- 
the inhabitants of that planet for almoft fifteen of our 
years, and as long invifible, by turns-, if its axis has no 
inclination to its ring ; but if the axis of the planet be in¬ 
clined to the ring, ex. gr. about thirty degrees* the ring 
will appear and difappear once every natural day to all the 
inhabitants within thirty degrees of the equator, on both- 
Tides, frequently eciipfing the Sun in a Saturnian day. More¬ 
over, if Saturn’s axis be fo inclined to his ring, it is per¬ 
pendicular to his orbit ; by which the inconvenience of 
different feafons to that planet is avoided. 
The ring, feen from Saturn, appears like a large lumi¬ 
nous arch in the heavens, as if it did not belong to the 
planet. To us, it is invifible when its plane paffes through 
the Sun, the Earth, or between them ; in the firft cafe, 
the Sun ihines only upon its edge, which is too thin to re¬ 
flect Aifficieru light to render it vifible; in the fecond cafe,, 
the edge only being- oppofed to us, it is not vifible for the 
fame reafon ; in the third cafe, the dark fide of the ring 
is expofed to us, and therefore, the edge being the only 
luminous part which is towards the Earth, it is inviiible on 
the fame account as before. The phenomena of Saturn’s 
ring are illuftrated in Jig . 2, of the Aftronomical-Plate V. 
Let S- be the Sun, ABCDBFGH Saturn’s orbit, and 
IKLMNO the Earth’s orbit. Both Saturn and the Earth 
move according to the order of the letters; and when Sa¬ 
turn is at A, his ring is-turned edgevvifeto the Sun S, and: 
he is then feen from the Earth as if he had loft his ring, 
let the Earth be in any part of its orbit whatever, except 
between N and O ;. for, whilft.it deferibes that fpace, Sa¬ 
turn is apparently fo near the Sun as to be hid in his beams. 
As Saturn goes from A to C, his ring appears more and 
more open to t-he Earth ; at C the ring appears mod open 
of all; and feerrrs to grow narrower and narrower as Saturn 
goes from C to E ; and, when he comes to E, the ring is 
again turned.edgewife both to the Sun and Earth y and, as- 
neither 
