A S T R O 
neither of its fides is illuminated, it is invilible to us, be¬ 
came its edge is too thin to be perceptible; and Saturn ap¬ 
pears again as if he had loft his ring. But, as he goes 
from E to Ci, his ring opens more and more to our view 
on the under tide ; and feems juft as open at G as it was at 
C, and may be feen in the night-time from the Earth in 
any part of its orbit, except about M, when the Sun hides 
the planet from our view. As Saturn goes from G to A, 
his ring turns more and more edgewife to us, and, there¬ 
fore, it feems to grow narrower and narrower; and at A it 
difappears .as before. Hence, while Saturn goes from A 
to E, the Sun fhines on the upper fide of his ring, and the 
under fide is dark; and, whilft he goes from E to A, the 
Sun fhines on the under fide of his ring, and the upper 
fide is dark. The ring difappears twice in every annual 
revolution of Saturn, viz. when he is in the nineteenth 
degree of Pifces and of Virgo, and when Saturn is in the 
middle between thefe points, or in the nineteenth degree 
either of Gemini or of Sagittarius, his ring appears moft 
open to us; and then its longed diameter is to its fhorteft 
as 9 to 4. On January 29, 1790, the ring pafled through 
the Earth; and the EaTth pafling from the northern or 
dark, to the fouthern or enlightened, fide of the ring, the 
ring then became vifible, and will continue fo till 1803. 
Obfervers have differed ten or twelve days in the time 
of the ring’s becoming invifible, owing to the difference of 
tiie telefcopes, and of the ftate of the atmofphere. Dr. 
Berfchel obferves, that the ring was feen in his telefcope 
when we were turned towards the unenlightened fide; fo 
that he either faw the light reflected from the edge, or 
elfe the reflection of the light of Saturn upon the dark 
fide of the ring, as we fometimes fee the dark part of the 
Moon. He cannot, however, fay which of the two might 
be the cafe ; efpecially as there are very ftrong reafons to 
think, that the edge of the ring is of fuch a nature as not 
to reflect much light. M. de la Lande thinks, that the 
ring is juft vifible with the belt telefcopes in common ufe, 
when the Sun is elevated three minutes above its plane, or 
three days before its plane paffes through the Sun ; and, 
when the Earth is elevated 2' 30" above the plane, or one 
day from the Earth’s pafling it. The total difappearance 
of the ring feems only to be owing to the imperfections of 
the telefcopes in common ufe among aftronomers ; for Dr. 
Herfchel, with his large telefcopes, has been able to fee 
it in every fituation. He thinks the edge of the ring is not 
flat, but fpherical or fpheroidical. 
In a paper in the Phil. Tranf. for 1790, Dr. Herfchel 
ventured to hint at a ftifpicion that the ring was divided; 
this conjecture was ftrengthened by future obfervations, 
after he had had an opportunity of feeing both fides of the 
ring. His reafons are thefe : 1. The black divifion upon 
the fouthern tide of the ring is in the fame place, of the 
fame breadth, and at the fame diftance, from the outer 
edge, that it always appeared upon the northern fide. 2. 
With his 7-feet reflector, and an excellent fpeculum, he 
faw the divifion on the ring, and the open fpace between 
the ring and the body, equally dark, and of the fame co¬ 
lour with the heavens about the planet. 3. The black di¬ 
vifion is equally broad on each fide of the-ring. From 
thefe obfervations, Dr. Herfchel thinks himfelf authorized 
to fay, that Saturn has two concentric rings, fituated in 
one plane, which is probably not much inclined to the 
equator of the planet. The dimenfions of the two rings 
are in the following proportions, as nearly as they could 
be afcertained: 
Infide diameter of the fmaller ring - 590° parts. 
Outfide diameter - - - 7510 
Infide diameter of the larger ring - 7740 
Outfide diameter - - - 8300 
Breadth of the inner ring ... 805 
Breadth of the outer ring - - 280 
Breadth of the fpace between the rings 115 
In the Mem. de 1 ’Acad, at Paris, 1787, M. de la Place 
fnppofqs, that the ring may have many divifionsj but Dr. 
N O M Y. 
Herfchel remarks, that no obfervations will juftify this 
fuppofition. From the mean of a great many meafures of 
the diameter of the larger ring, Dr. Herfchel makes it 
46-677" at the mean diftance of Saturn. Hence its dia¬ 
meter is to the diameter of the Earth as 25-8914 is to 1. 
From the above proportions, therefore, the diameter of 
this ring muft be 204,883 miles, and the diftance of the 
two rings 2839 miles. 
The ring, being a circle, appears elliptical merely from 
its oblique poiiticn. Dr. Herfchel adds, “ Some theories 
and obfervations of other perfons lead us to confider the 
queftion, Whether the conftruCt ion of this ring is of a nature 
fo as permanently to remain in its prefent ftate ? or Whe¬ 
ther it be liable to continual and frequent changes, in fuch 
a manner as, in the courfe of not many years, to be feen 
fubdivided into narrow flips, and then again as united into 
one or two circular planes only ? Now, without entering 
into a difeuflion, the mind feems to revolt, even at firft: 
fight, againft an idea of the chaotic ftate in which fo large 
a mafs as the ring of Saturn muft needs be, if phenomena 
like thefe can be admitted. Nor ought we to indulge a 
fufpicion of this being a reality, unlefs repeated and well- 
confirmed obfervations had proved, beyond a doubt, that 
this ring was actually in fo fluctuating a condition.” But, 
from his own obfervations, he concludes, “ It does not ap¬ 
pear to me that there is a fufficient ground for admitting the 
ring of Saturn to be of a very changeable nature, and I 
guefs that its phenomena will hereafter be fo fully explain¬ 
ed as to reconcile all obfervations. In the mean while, 
we muft withhold a final judgment of its conftruCtion, till 
we can have more obfervations. Its divifion, however, 
into two very unequal parts, can admit of no doubt.” 
Of the Satellites of Saturn. 
In the year 1655, Huygens difeovered the fourth fatel- 
lite of Saturn ; and publiftied a Table of its mean motion 
in 1659. In 1671, M. Caftini difeovered the fifth, and 
the third in 1672; and, in 1684, the firft and fecond; and 
afterwards publifhed Tables of their motions. He called 
them Sidera Lodoicea, in honour of Louis le Grand, in 
whofe reign, and obfervatory, they were firft difeovered. 
Dr. Halley found by his own obfervations in 1682, that 
Huygens’s Tables had confiderably run out, they being 
about fifteen degrees in twenty years too forward; and 
therefore he compofed new Tables from more correct ele¬ 
ments. He alfo reformed M. Caflini’s Tables of the mean 
motions; and about the year 1720, publiftied them a fe¬ 
cond time, corrected from Mr. Pound’s obfervations. He 
obferves, that the four innermoft fatellites deferibe orbits 
very nearly in the plane of the ring, which he fays is, as 
to fenfe, parallel to our equator; and that the orbit of the 
fifth is a little inclined to them. 
On June 9, 1749, at 10I1. Mr. Pound found the diftanoe 
of the fourth fateliite to be 3' 7” with a telefcope of 123 
feet, and an excellent micrometer fixed to it; and the fa¬ 
teliite was at that time very near its greateft eaftern digref- 
fion. Hence, at the mean diftance of the Earth from Sa¬ 
turn, that diftance becomes 2' 58-21''; Sir Ifaac Newton 
makes it 3' 4”. 
By comparing the fatellites with the ring in different 
points of their orbits, and the greateft minor axes of the 
ellipfes which they appear to deferibe compared with the 
major axes, the planes of the orbits of the firft four are 
found to be very nearly in the plane of the ring, and there¬ 
fore are inclined to the orbit of Saturn about thirty de¬ 
grees; but the orbit of the fifth, according to M. Caftini, 
jun. makes an angle with the ring of about 15 0 . 
M. Caftini places the node of the ring, and confequently 
thofe of the four firft fatellites, in 5ft 22 0 . upon the orbit 
of Saturn, and 5ft 21 0 . upon the ecliptic. M. Huygens 
had determined it to be in 5ft 20 0 . 30'. M. Maraldi in 
1716 determined the longitude of the node of the ring up¬ 
on the orbit of Saturn to be 5ft 19 0 . 48'. 30”. and upon 
the ecliptic to be 5ft 16 0 . 20'. The node of the fifth fa^ 
tellite is placed by M. Caftini in jf. 5 0 . upon the orbit of 
1 Saturn. 
