the Surface of the Sun. The Sun muft bear a resemblance to an impure Liquor, which bubbles up and throws out Froth, and of the Froth which iffues out of the Sun, must be formed opaque and black Bodies capable of ftopping the Action of an infinity of Rays, of obfcuring divers parts of the Sun's Surface, and of presenting to our Eyes by that means divers heaps of Spots, fome more obfcure, and others more clear.

In short, these forts of Froth may wander at the pleasure of inflamed Waves, augment and diminish. Hence the changes of bignefs and fituations in the Spots. The Froth may come out of all parts of the Sun, as it comes out of bubbling Liquor. Hence the Spots which one fees arife at once in divers parts of the Sun. The Action of the Liquid, which undermines them according to their Depth, may diffolve, and at laft render them imperceptible by diffolution, and make them to pass again into the Subftance of the Liquid out of which they fprung up like Froth out of a Liquor that boils. Hence the Spots disappear

at once.

The Spots of the Sun are generally environed with a kind of Cloudinefs, not fo black as the Spots themselves.

Arift. Because probably the Extremities of the Spots are tranfparent, or are covered in part with a luminous Liquid. But have these Spots only irregular Motions?

Eudox. Ordinarily we fee the Spots advance from the Eaftern Limb of the Sun toward the Weftern". And often times have they been seen to make an intire Revolution round the Sun in about twenty seven days and an half".

Arift. Does the Sun itself then turn round upon its own Centre in twenty seven days and an half?

Eudox. The Spots of the Sun cannot, as they do, make a Revolution round the Sun in about twenty seven days and an half ; that is, in twenty seven days, twelve hours, and 20 or 30', unless the Sun it felf turned upon its own Axis in the fame Space, fince they float upon the Liquid of this Planet. In fhort, we perceive no interval between them and this Liquid. Being obferved from divers parts of the Earth at the fame time, they appear in the fame point of the Sun. They find no less distance in them than in this Planet. Therefore the Sun turns round upon its own Axis in about twenty feven days and a half.

1

And it turns after fuch a manner, that the upper part moves from Weft to East, and the lower part from Eaft to Weft. For we only fee the inferiour part, and we fee the Spots move from the Eaftern border of the Sun toward

Le P. Taquet. Aftron. 1.8. Tract. 3. p. 7.

n Decouv. de la Lum. cél. qui paroît dans le Zodiaque, p. 17. · Receuil d'Obferv. Hift. de l'Acad. 1702.

P. 122.

P. 73. 1706.

the

the Western, and afterward to return again by the Eastern. And fince Spots, which pass through the Center of the Sun, in making their Revolution, defcribe a Line which makes with the Plane of the Ecliptick an Angle of seven Degrees and an half, the Equator of the Sun, or the Plane of a Circle, which it defcribes in its Revolution, muft make, with the Ecliptick, an Angle of the fame bigness.

Will you tell me, Ariftus, why the Motion of the Spots appears flower toward the extremities of the Sun's Difcus than toward the middle?

Arift. As the Sun is round, and the Spots ascend in regard to us, or descend toward the Borders, they are fenfibly a longer time in the fame visual Rays, without producing confiderable changes in the Eye. Hence their apparent flowness.

But, Eudoxus, could not our Eyes which have discovered what paffes in the Sun, find fomething fingular in the Stars?

Eudox. Another day we shall speak of the Stars. To-day let us talk of the Dauphin, who is the Object of our Vows. He is a new Sun, whose presence will charm the People. Let us before-hand taste the pleasure which he is going to diffuse over our Hori

zon.

• Scheiner. Rofa Urfina. Taquet. Aftron. p. 345. M. Caffini. Découv. de la Lum. cél. &c. p. 17, 63. Rec. d'Obferv. par Meff, de l'Acad. Hift. de l'Acad. 1701. p. 105.

CON

Eudox.

ET us, begin, Ariftus, with calling to mind the Revolu tion of the Planets and the Sun, their Diftance and Bignefs; and the Knowledge of the Stars will thereby be rendered the more cafy.

1. According to the Obfervations of the moft skilful modern Aftronomers, the Planets which turn upon their own Axes, as the Sun, make this Revolution after the fame manner; fo that the upper Hemifphere moves from West to Eaft, and the lower Hemifphere from East to Weft, fince we fee their Spots move in the lower Hemifphere from Eaft to West, disappear in the Western Limb, and appear again in the Eaftern. The Satellites have alfo a Direction from the Weft toward the Eaft in the upper part of their Orb, and a contrary Direction in the lower *.

2. We know the distance of the Planets by the Parallax, Fig. 16. The Parallax is the

*Hift. de l'Acad. 1707.p.93.1716. P. 57.

I

distance