Euphrof. Befides the dark Shadow MCO, there is a fainter Sort of Shadow A M O B; pray, what am I to understand by that?

Cleon. That is called the Penumbra, or partial Shadowo, because a Perfon any where on the Earth's Surface between C and A will fee only a Part of the Sun's Face eclipfed; but fo much a greater Part as he is nearer to C, or a lefs Part as he is nearer to A; for 'tis manifest when the Spectator is at A, he will fee no Eclipfe at all, but the whole Face of the Sun will there be visible, fince the Line AME touches the Extremities of the Moon and Sun that are next to each other.

Euphrof. I apprehend you very well; for fince in any Part between C and A there will be more or lefs of the Sun's Light, the Shadow arifing from the eclipfed Part will not be fo dark as at C, where there is no Light, or next to none; and the fame I fee will happen all around the dark Shadow to the Diftance of CA or CB.

Cleon. I am glad to fee you understand the Nature of an Eclipse fo well; you will as eafily conceive that this penumbral Shadow will be darker about C, and lefs fo towards the Extremities of the Cone A and B, where it becomes infenfible.

Euphrof. I do, Cleonicus; but fee, the Time is at Hand for the Eclipfe to begin-It wants 5 Minutes by my Watch,

Cleon. Well, we are prepared for it, happen as soon as it will; I have fixed the Telescope in a proper Pofition for viewing it; and thereby you will fee it in the Heavens. I have alfo darkened the Chamber, wherein you will fee the Eclipfe in Miniature very perfectly; and have fo ordered it that you only need to step out of one Room into

another to fee both.

Euphrof. Dear Cleonicus, I am greatly obliged to you; but let me feat myself at the Telefcope to obferve the Beginning.

Cleon. Do fo immediately; there is a Piece of dark Glafs before the Eye-Glafs in the Telescope, through which you may view the Sun without hurting your Eyes.

Euphref. Very good, Cleonicus; let me view himhim——— I fee his glorious Face, and the several Spots which beautify it—there is yet no Appearance of an Eclipse. Clean. In half a Minute you'll fee it.

Euphrof. I do:-The Moon just touches him on thẹ right Side and covers a very fmall Part-let

me fee it in the Chamber

Cleon. Look in

Euphrof. 'Tis just as I saw it at large in the Telescope; how beautiful it appears in that small Picture! But here it begins on the left Side, how is that?

Cleon. That is, because the Image of the Sun is inverted by the fingle Glafs in the Scioptric Ball-See, there is a large Spot, which the Moon will presently hide,-view it in the Telescope

Euphrof. I will-the Moon is almost upon it-it difappears also another fmall Spot below-fhe advances apace-the Sun is near one quarter eclipfed-I'll see it now in the dark Chamber

Cleon. Do; I'll look through the Tube-Tell when you fee a Spot just going to be hid

Euphrof. I will the dark Circle is very near one on the upper Part

Cleon. I fee it,-fpeak when it difappears

Euphrof. The Moon just touches it 'tis gone.

Cleon. I obferved it the Inftant you fpoke; from hence you fee how truly every Thing in the Heavens is reprefented in the large Picture of the Sun, in the Focus of a proper Glass, when the Room is dark.

Euphrof. Very finely, indeed; I never obferved an Eclipfe with fo much Pleasure and Exactnefs before But fee, methinks it begins to appear fomewhat darkish, or elfe 'tis my Fancy

Clean: The Sun is now about two thirds eclipfed, and the Day-light begins to be fenfibly diminished, and will be fo in a few Minutes.

Euphrof. 'Tis darker than it was-I'll view the Sun again-he appears horned like the Moon in her laft Quar ter; a great Clufter of Spots will be hid by-and-by.

Cleon. They will fo-the Darkness increases very fenfibly-the Air feems obfcured, you will quickly fee the Stars

Euphrof. The Stars! Will it be so dark as to make them vifible?

Cleon. Vifible! yes, for a confiderable Time; you will fee Day converted into Night

Euphrof. Blefs me, you make me fhudder at the Thought The Spots are gone, Cleonicus.

Cleon. They are, I fee, in the Image-fee, from the Window, how the People ftare and are furprized in the Street

Euphrof. Surpriz'd, and well they may; I believe they never saw it so dark in the Day-time before-How dark it is!

Cleon. It will be much darker by-and-by-in about three or four Minutes the Sun will be totally eclipfed

Euphrof. I find it cold too, as well as dark, Cleonicus. Cleon. It is cold-fee the Owl flying over yonder Meadow-fhe thinks 'tis Night.

Euphrof. I fee her-fhe halloos too-Hark! there's a general Murmur in the Streets-I heard one fay he believed the World was going to be at an End

Cleon. Very likely; they can't tell what to think of a Thing fo very strange-See, yonder, a large Star appears→→ Euphrof. I fee it-and many more-I believe the Sun is nearly quite eclipfed-The Birds chirrup, cry, and fly to the Hedges, as if very much frightened

Cleon. They really are fo-the Sun is now totally eclipfed.

Euphrof. Look, fee how the Beasts run under the Trees-what do the poor Creatures think!

Cleons Think! they can't tell what the Matter is, they know 'tis fomething very extraordinary-There has been many a Night not fo dark as it is now,

Euphrof. That I am fure of-well 'tis very furprizingCleon. So it is, to fee the two great Lights of Heaven. in a Manner both extinguished!

Euphrof. The greatest Darkness is over I fee-Pray, was it ever fo dark in an Eclipfe before?

Cleon. Yes, and fometimes of longer Continuance. Euphrof. Do there often happen fuch very great and total Eclipfes of the Sun ?

Cleon. To fome Part of the Earth or other there does ; but not in any one Place; for in England I know not of

L 4

above

above two total Eclipfes that have happened in this or the laft Century, viz. one in 1652, on Monday March 29; and the other in 1715, 21st of April, when it was total about two Minutes of Time. The next great Eclipfe happened in 1737, Feb. 18. Another pretty large one happened in 1748 on the 13th of July; befides thefe, we have no other to happen 'till the Year 1764, when more than five Parts out of fix of the Sun's Diameter will be eclipfed *.

Euphrof. The Thing would not be fo ftrange if it happened often.-The Sun recove.s his Splendor apácethe Stars begin to disappear; and the Beasts retreat from their Coverts to the open Fields again.

Cleon. Yes, 'twill foon be Day once more; thefe ecliptic Nights laft but a little Time; they are scarce sufficient for a Nap

Euphrof. Pray, how large may the dark Shadow of the Moon be on the Part of the Earth which it sweeps ?

Cleon. When at a mean, it takes in the Compass of about 150 Miles; and when greatest it extends to 220 Miles.

Euphrof. But what you call the Penumbral Shadow, I fee, is vaftly larger

Cleon. Yes, it is fo; it involves a Part of the Earth's Surface, no less than about four thousand three hundred and ninety-feven Miles over, at a Mean; and when greateft, it takes in about 600 Miles more; and therefore all People about us, to the Distance of near two thousand five hundred Miles, will fee the Sun eclipfed more or less.

Euphrof. The Eclipfe, I fee, is nearly at an End; I do affure you, Cleonicus, I never spent 24 Hours with more Pleasure and agreeable Surprize than now.If you pleafe, we will now go to drink Tea, and then I fhall trouble you with a few more Questions about an Eclipfe of the Moon.

Clean. With all my Heart, my Euphrofyne; you know nothing gives me a greater Pleasure than to fatisfy your Enquiries about natural Things.

This proved a most beautiful Annular Eclipfe, for the Moon's Difk being at that Time lefs than the Sun's, left a Ring on the Sun's Limb not eclipfed.

DIALOGUE VI.

Of an ECLIPSE of the MOON.

A

Euphrofyne.

S the Eclipfes of the Sun which are vifible to us muft always happen in the Day-time, fo those of the Moon muft ever be in the Night, I conceive, Cleonicus. Cleon. And very juftly, Sifter; for fince an Eclipse of the Moon can never happen, but when the Moon is at Full; and fince the Moon is then in Oppofition to the Sun, fhe will rife when the Sun fets; therefore no Eclipfe of the Moon can be seen by us till after Sun-fet. But the Moon may, and often does, rise and set eclipsed as well as the Sun.

Euphrof. As I faid before, I need not afk how an Eclipse of the Moon happens, for 'tis plain from the Scheme, that it is by the Moon's paffing through the dark Shadow of the Earth FGLN.

Cleon. It is fo; for the Earth at that Time coming between the Sun and Moon, and being much larger than the Moon, does caft fo large a Shadow as often involves the Moon a confiderable Time therein. According to Lucretius:

So whilft the Moons their monthly Courses run Within the Reach of Earth's dark shadowing Cone, The Earth, revengeful, flops the freaming Light, And hides the fick'ning Moon in Gloom of Night. Euphrof. The fick'ning Moon. I think it is a very beautiful Metaphor on that Occafion.

Clean. It is fo; and it is only a Metaphor in the Poet; but the Vulgar among the Ancients did indeed believe that the Moon was actual y fick, and laboured as in an Agony, and fuffered a Kind of Death.

Euphrof. Indeed! Pray, how came they by fuch a Notion?

Cleon. Their Superftition taught them to look on the Moon as the Goddefs who prefided over the Earth; and their Credulity (for the Ignorant believe any Thing) made them fit Fools for Magicians and Inchanters to work upon; for thefe deceitful Wretches made them believe

that