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النشر الإلكتروني

DIALOGUE IV.
The Speculation of the Stars continued.

Euphrosyne. AFTER a few tempestuous Nights, I see the HeaA vens begin to refine, and the azure Expanse renews its Sparkling Glory. We will, therefore, now re-assume qur Speculation of the Stars, if you please, Cleonicus, and consider divers other Circumstanices, of which I have pot yet a good Notion.

Cleon. You engage me with a great deal of Pleasure, Euphrosyne; I shall gladly impart to you all that I know concerning the Stars.

Euphros. The next Question then that I would ask is, whence comes it to pass that each Star twinkles fo vehemently in a clear Night?

Cleon. The Twinkling, or Scintillation of the Stars, arises from the continual Agitation of the Air, or Atmosphere, through which we view them; for the Particles of the Air are always in Motion, and will cause a Twinkling in any distant'luminous Bodies, that are apparently less than those opake Particles, as the Stars all are ; but the Planets, that appear larger, can suffer no Occultation by them, and therefore admit of no such Scintillation.

Euphrof. Then none of the Planets twinkle in the darkest Night, do they ?

Cleon. No; and by that you may distinguish them at any Time from the fixed Stars.

Euphrof. Pray, let me try that.

Cleon. You shall; take this Telescope, and look at yon 'Sparkling Star.

Euphroj. I see which you mean, give me the Glass I see it plainly-It appears very steady, nor does it sparkle at all—yet it appears with a very strong Light-But this Telescope does not magnify much, I believe, for I can't perceive that the Star is bigger than it appears without it.—,

Cleon. This is not the Fault of the Glass, it magnifies very much; but were it to magnify a hundred Times more, or a thousand, the Star would still appear but as a Point; for by Reason of its immense Distance, it eludes the Force of any magnifying Glass, Yea, on

the

the contrary, the Stars are rather diminished in Appearance, by taking off their sparkling Luftre.

Euphrol. Well, then, the next Thing I would enquire is, why they are called Fixed Stars?

Cleon. Because they do not, like the Planets, change their Places, or alter their Situations in the Heavens, but keep at all Times the same Distances and Position among themselves; that is, the fame Star, at the same Time of the Year, always is seen in the same Place, and at the fame Distance from others about it.

Euphrof. I know you'll resolve the apparent nocturnal Motion of the Stars, from East to West, into a Consequence of the diurnal Motion of the Earth the contrary Way; but how happens it that at one Time of the Year we see one Set of Stars in the Sky, and at another Time of the Year another?

Cleon. This arises from the annual Motion of the Earth, and which I will explain to you by this little Scheme; where S is the Sun, and A, B, C, D the Earth, in four Positions of its Orbit; also E F GH the Firmament of the Stars, at an infinite Distance.

Now the Earth in each Situation appears half enlightened, and half dark, representing Day and Night. And when it is at A, the Sun will appear at Noon in the Heavens at G, and will obscure all the Stars in the Hemisphere, FGH; whereas at Midnight the Point of the Heavens E, will be in the Meridian, and then all the Stars in the other Hemisphere, F, E, H, will be visible. Do you apprehend me?

Euphrof. Yes, pretty well ; pray proceed.

Cleon. Then when the Earth, three Months after, is come to the Situation B, the Sun at Noon will be seen at H, and, all the Heavens, G H E, will be Day; and over all the other Half, E F G, the Stars will glitter at Night.

Euphrof. Then I perceive the Stars in the Quarter FG, will now be visible, which (in the former Position) were not; and those in the Quarter H E, will become obscured by Day-light.

Cleon. You conceive the Thing admirably well, my Euphrosyne : In like Manner when the Earth is at C, the Heavens, HEF, will be Day, and F G H Night, where all the Stars will shine.

Euphrof. Then that Part of the Heavens which was Day when the Earth was at A is now Night, and so the Stars which were all then invisible are now visible, and the contrary.

Cleon. Very right, Sister, that is the Case; and lastly, when the Earth is at D, the Stars in the Hemisphere, EFG, will be obscured by Day-light, and those in GHE will all be visible in the Night.

Euphrof. Well, I am fully satisfied in this point, Cleonicus; but why do I see some Stars constantly all the Year round, and others but at different Times and Seasons ?

Cleon. You might have added too-and fome Stars not at all. But as this depends on some Understanding of the Doctrine of the Sphere, you will apprehend it much better when I shall one Day or other explain to you the Use of the Celestial Globe.

Euphrof. I am willing to wait all proper Opportu. nities, and am obliged to you for chusing them. And now I suppose there remains nothing besides relating ta the Motion of the Stars to be considered ; therefore

Cleon. Hold, Sister; before we leave this Subject, I shall just observe to you, that there is only one Star in all the visible Heavens which seems to have no Motion at all.

Euphrof. Indeed! Pray, which is that?

Cleon. It is that commonly called the North Pole, or more properly the Polar Star.

Euphrof. Be so good as to thew it to me.

Cleon. It is that small, but bright Star, which you fee yonder, full North, amidit many other, but smaller Stars ; it is ever pointed to by thoie two large bright Stars in Charles's Wain, which you obierve a little to the Left Hand.

Euphrof. I see the Star you mean, very plainly; and do you say it has no Mution ?

Cleon. It does not appear to move either with the diurnal or annual Motion, as all the other visible Stars do ; but view it at what Tim: of the Night or Year you will, you see it always in the same Place.

Euphrof. But you seem to intimate by your Way of speaking, that it has some sort of Motion or other ; has it not?

now ve Motion make like o

Cleon. It has; but such an one as is not sensible in 1 long Course of Years, and arises from a Cause that you must stay a while before you can well understand it.

Euphrof. To what End then do you inention it to me, Cleonicus?.

Cleon. Because there is something very surprising in the Consequence thereof: For this Star,' though it be now very nearly in the North Point of the World, has such a Motion round a certain Point in the Heavens, as will in Time make it to circula e through the several Parts of the Heavens like other Stars.

Euphrof. Say you so; will the North Star in Time be seen Southward of us? Pray, in how long a Time?

Cleon. In the Space of twelve Thousand nine Hundred and fixty Years ; for in double that Time, viz. in twentyfive Thousand nine Hundred and twenty Years, it makes one Revolution, which is called the Great, or Platonic Year, from Plato the Philosopher, who, with other of the Antients, supposed that after this Period all worldly Changes would return in the same Manner and Order as before.

Euphrof. Is this a real, or only an apparent Motion of the Stars?

Cleon. Apparent only, as are both the other. And thus much of the Motion of the Stars, of which Dryden has these Lines,

As when the Stars in their ethereal Race,
At Length have rolld around the Liquid Space,
At certain Periods they resume their Place.
From the fame Point of Heavn their Course advance,
And move in Measures of their former Dance.

Euphrof. I observe a manifest Difference in the Colour of the Stars, some look red, others pale; pray, what can

co Cleon. caning of thatred, other Diference internet

Cleon. You ask a Question I can't refolve.—There is somewhat undoubtedly very different in the Nature both of the Matter and Light of those Stars or Suns; but what that is, their Maker only knows.

Euphrof. I have had my Eye fome Time upon a Kind of brightis misty Spot, which at first Glance seems like a Star; pray, is it a Star, or what is it?

Cleon. I see what you mean; it is indeed called a nebulous, or misty Star ; but it is not a Star properly speaking : You'll have a better Notion of it when you view it with a Telescope...

Euphrof. Give me the Tube, and I'll view it-Bless me, what do I fee !—The Glass is covered with Stars as thick as Bees in a Swarm.-Very small Stars, yet very diftinct.—I do fee now what it is, indeed-A compound Star, consisting of Multitudes of single ones.--Well, this is a wonderful Sight, on my Word, Cleonicus. :)

Cleon. There is nothing more curious among the Stars, in my Opinion. There are reckoned about fix or seven of these nebulous Stars in the Heavens; in some of which there appears a bright, lucid Part, in which some Stars appear, as fron a white Cloud, and these are reckoned to be Regions of a peculiar Nature, which enjoy a native Light, and an uninterrupted everlasting Day.

Euphrof. How infinitely various, amazing, and unaccountable are the Works of Nature! But cafting my Eyes on the seven Stars, puts me in Mind to ask a Question I have long intended ; and that is, Why are they called the seven Stars, when no Person, I believe, can tell above fix?

Cleon. In Answer to this, I shall at present only fay, that in former Times, 'tis probable, there were seven to be seen, one of which afterwards became extinct, , and was never more seen ; and that as long since as Ovid's Days (who lived in the Time of our Saviour) as is evident by these Verses in his Fasti. .

Now rise the Pleiades, thojé Nymphs fo fair,

Once feven number'd, now but fix there are Now though there appear but six Stars in this Constellation to the naked Eye, yet take the Telescope and view them, and you will discover many more.

Euphrof.' Pray, give it me then; I'll view them.O surprizing !-What a Number do I see! I can tell near twenty --They fill a greater Space than the Glass will take in.-Some are very large, others small. There are so many, I can't number them all.

Cleon. I believe so, Euphrosyne ; for Dr. Hook tells us, that with a twelve Foot Tube he counted no less than 98 Stars; and making Use of longer Telescopes, he dif

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