When in this situation it had lost its ruddy color, and appeared perfectly white, or of the color of the moon At its emersion nothing particular was observed; the star shone forth at once with its usual color and brilliancy. The sky was beautifully clear.

PHENOMENA PLANETARUM.

Mercury at his greatest south latitude on the 1st of this month. In conjunction with Venus on the 2nd, and with Saturn on the 5th. Inferior conjunction with the sun at 2 in the morning of the 9th. Stationary near c, in Leo, on the 17th. Ascending node on the 20th. Greatest elongation, (17° 52',) as a morning star, on the 24th. In perihelion on the 25th. In conjunction with Saturn at 10 in the morning of the 30th, difference in declination 9'.

Venus in conjunction with ŋ, in Virgo, at 11 in the morning of the 12th, difference of latitude 10'.

Phases of Venus.

The proportions of the bright and dark phases of Venus are as follow::

September 1st.—Illuminated part = 11.8222

Mars, on the 30th, approaching & in Taurus.

The Asteroids.

Hrs. Min.

Vesta, 5th day. Right Ascension 12 8. N. Declin. 4° 32'

Vesta and Juno in conjunction on the 25th, difference of declination about 14 degree.

Pallas in opposition on the 17th, north of 27 in Pisces.

Jupiter in opposition to the sun at 2 in the afternoon of the 16th, near 20, in Pisces, and the asteroid Pallas.

Eclipses of the Satellites of Jupiter.

IMMERSIONS.

First satellite, 6th day at 50 min. 19 sec. after midnight.

2 morning.

Third satellite, 6th day at 40 min. 38 sec. after 10 night.

14th...... 42

Fourth satellite, 16th...... 41

....

EMERSIONS.

... 2 morning.

1

First satellite, 23rd day, at 21 min. 45 sec. after 1 morning.

Saturn in conjunction with the sun at 5 in the morn

ing of the 11th.

FORM OF SATURN'S RING.

The ring of Saturn is scarcely perceptible during the month, as appears from the following proportions of the semi-transverse to the semi-conjugate axis :

September 5th.-Semi-transverse axis

Semi-conjugate axis

36".77

0 .90

The earth will be in the plane of the ring of Saturn at 2 in the morning of the 30th of this month, consequently the ring will be invisible, excepting under peculiar circumstances. In powerful telescopes the

edge of the ring has been perceived, appearing as a fine luminous line across the disc of the planet; in the pre

sent instance, the position of the planet will be very unfavorable for witnessing this interesting phenomenon, -Saturn being so near the solar

rays.

This invisibility occurs when the plane of the ring passes through the sun, or the earth, or between them; in the first case, the sun shines only upon the edge of the ring, which is too thin (less than 1" in thickness) to reflect sufficient light to render it visible; in the second case, the edge only being opposed to us, it is not visible for the same reason; in the third case, the dark side of the ring is exposed to us, and, therefore, the edge being the only luminous part which is towards the earth, it is invisible on the same account as before.

The ring, however, has been seen, when the earth was on the unenlightened side, which must either have been from the light reflected from the edge, or else the reflection of the light of the globe of Saturn upon the dark side of the ring,-analogous to the secondary light of the moon.

The ring may be visible when the sun is elevated 3' above its plane, or three days before its plane passes through the sun, and when the earth is elevated 2′ 20′′ above the plane, or one day from the earth passing it.

That the ring is exceedingly thin, is evident from the satellites being seen to pass behind and before the ring, in such a manner, that they served as an excellent micrometer to measure its thickness by. The following observations, by Herschel, are very interesting:

July 18, 1789, at 16h. 41m. 9s. sidereal time, the third satellite seemed to hang upon the following arm, declining a little towards the north, and was seen gradually to advance upon it towards the body of Saturn;

but the ring was not so thick as the lucid point. July 23rd, at 19h. 41m. 8s. the fourth satellite was a very little preceding the ring, but the ring appeared to be less than half the thickness of the satellite. July 27th, at 20h. 15m. 12s. the fourth satellite was about the middle, upon the following arm of the ring, and towards the south; and the second at the farther end, towards the north; but the arm was thinner than either. August 29th, at 22h. 12m. 25s. the fifth satellite was upon the ring, near the end of the preceding arm, and the thickness of the arm seemed to be about one-third or onefourth of the diameter of the satellite, which, in the situation it then was, he took to be less than one second in diameter. At the same time, the first appeared at a little distance following the fifth, in the shape of a bead upon a thread, projecting on both sides of the same arm; hence, the arm is thinner than the first, which is considerably smaller than the second, and a little less than the third. October 16, this celebrated astronomer followed the first and second satellites up to the very. disc of the planet; and the ring was then so extremely faint, as not to obstruct his seeing them gradually approach the disc. These observations are sufficient to show the extreme thinness of the ring. But Herschel further observes, that there may be a refraction through an atmosphere of the ring, by which the satellites may be lifted up and depressed, so as to become visible on both sides of the ring, even though the ring should be equal in thickness to the smallest satellite, which may amount to a thousand miles.

In October, 1714, when the plane of the ring very nearly passed through the earth, and was approaching