Fig. XXIV, you obferve the Earth E, in her annual Orb AB, moving about the Sung at the fame Time, you obferve the Moon moving about the Earth in her Orb: Now when the Moon is in Conjunction with the Sun, i. e. when she is juft between the Earth and Sun, and is what we call the new Moon, as at M; then 'tis evident her Shadow will fall on the Earth at E, and confequently will hide fome Part of the Sun's Body from those who dwell on that Spot and this is what they call an Eclipfe of the Sun, but is properly an Eclipse of the Earth; for you fee 'tis the Earth that is really darkned, and not the Sun: Alfo 'tis evident, when the Moon is in the oppofite Part of her Orb at N, in direct Oppofition to the Sun, that then the Earth being exactly between the Sun and the Moon, will caft her Shadow on the Moon; and the Moon being thus overwhelmed in the Shadow of the Earth, will appear dark or dusky, and is properly faid to be then eclipsed.

A. This, indeed, is fo plain and evident by a bare Inspection of that Figure, that I believe none can look on it, and not apprehend the Manner and Caufe of Eclipfes. Pray can you tell the Quantity of Eclipfes ?

B. Yes The dark Shadow of the Moon covers a Part of the Earth's Surface, about

Of Eclipfes, and Saturn's Ring. 127

180 Miles in Diameter, and moveth at the Rate of 2 104 Miles an Hour: But the partial or penumbral Shadow, extends to the Wedth of 4900 Miles: And as to lunar Eclipfes, the Diameter of the Earth's Shadow at the Moon, is near near 3 Times greater than the Diameter of the Moon; and therefore the Moon, in central Eclipfes of her Disk, is totally darkned, or eclipsed, for fome Time."

A. So, I fuppofe, Eclipfes happen to Saturn and Jupiter, on account of their Moons; and likewife to the Moons themfelves, as well as to our Moon.

B. Yes; but the Eclipfes of thofe Planets are much more frequent than of our Earth, the Number of Moons, and their quick Circulations, neceffarily making them fo; alfo the Eclipfes of thofe Moons or Satellites are very frequent, one or the other being continually paffing through the Shadow of their Primary.

A. Well, leaving the Moons and their Eclipfes; pray let me hear a Word of two about the wonderful Ring of Saturn that you mentioned juft now.

B. This moft furprising Phænomenon of all the vifible World, was first discovered about 100 Years fince: It is of a prodigious Size, great Breadth, and vaft Compass; it is faid the Distance of the inner Border of the Ring, from the Body of Saturn, is equal

equal to the Breadth of the Ring it felf, each being computed to be at least 21000 Miles; though others make the Interval between the Ring and Saturn's Body to be 210265, and the Breadth of the Ring to be 29200 Miles; its Thickness is unknown, as being too little for Obfervation; it hath a Variety of Afpects, fometimes appearing a larger Ellipfis, then a fmaller; fometimes only as a strait Line, and fometimes not visible at all: These are the most remark able Particulars of this Prodigy of Nature known by us; as to the Matter of which it doth confift, that is not known by any: I have here given you a Representation thereof in Fig. XXV.

A. This is astonishing, and full of Wonder and Amazement indeed! But did not you say somewhat of a like Nature pertained alfo to Jupiter; pray what are those Belts of his you mentioned but now?

B. Those Belt-like Appearances of Ju piter are fuppofed to adhere to, or be in the Surface of his Body, and not at a Distance from it, as the Ring of Saturn is from him; they are 4 or 5 in Number, and appear as reprefented on Jupiter's Body in Fig. XXV.

A. And, pray, what are thofe Belts fuppofed to be?

B. Some have imagined they are long Canals of fome fluid Matter, or Water;

and,