« السابقةمتابعة »
Solar ones, and as easily understood. But unless I could tell which were greatest, the Sum of the half Diameter's · of the Sun and Moon, or of the Shadow and Moon, I can't tell which would be greatest, the Limits of a Solar er Lunar Eclipse.
Cleon. Though the latter Sum be in itself greater than the former, yet the former, with Respect to the visible Latitude of the Moon, is greater than the latter, in Regard of her true Latitude; and therefore the Limits of a Solar Eclipse exceed those of a Lunar one.
Euphrof. I should be glad to know in what Time the Sun moves over the ecliptic Limit CG.
Cleon. There Limits are somewhat variable ; but when CG is least, the Sun takes up about 28 Days in pafling over it, and 32 Days when greatest.
Euphrof. And pray what is the Time between one new Moon and another?
Cleon. Twenty-nine Days and an half.
Euphrof. Why then, when the Limit CG is greatest, there must necessarily be an Eclipse of the Sun during his Stay within that Limit; but when it is least, I perceive it is posible there may be no Eclipse of the Sun that Node.
Cleon. 'Tis indeed possible there may not; but the Chance there will not is so very great, that it was never known to happen, I believe. On the other Hand, when the Limit is least there is one Eclipse very certain, and there may be two when greatest; and this sometimes happens, as in the Year 1736, 1743, &C. But these twin Eclipses are very small, and almost always to us invisible.
Euphrof. Of all this I conceive the Reason pretty well, and now for the other Node : Pray how long is the Shadow of the Earth within the Lunar Limit OQ?
Cleon. This Limit is also variable; and when greatest, the Shadow pafleth it in 24 Days; and when leaft, in 19 Days.
Euphrof. Then since from Full Moon to Full Moon there is 29 Days and an half, if the Full Moon should happen in the Beginning of the Limit, as at N, before the Moon could again return to the fame Node, the Shadow would be past the other Limit Q; and so there
.? the Instay how", pretty
Cleon. Pesho Lunar Es posible, the at all.
would be no Eclipse of the Moon, in such a Case, at that Node, even when the Limit is the greatest of all.
Cleon. Very well observed, Euphrofyne ; nor can there ever be two Lunar Eclipses together at the fame Node, when the Limit is greatest ; so that upon the whole you see there can be but one Eclipse of the Moon within the Lunar Limits, and sometimes none at all.
Euphrof. Then I see 'tis possible, that in some Years there may be no Lunar Eclipse at all.
Cleon. Yes, it is; and thus it happened in the Years 1734, 1738, 1745, 1752, and in the present Year 1756, and will again happen in 1763; for in these Years there was no Eclipse of the Moon; and but two of the Sun, and both invisible to us, except that of August the 3d, 1738.
Euphrof. We find by Experience that the Solar and Lunar Eclipses happen both at the same Times of the Year, which is also evident from the Instrument.
Cleon. It is so ; for the new Moon, which obscures the Sun in the Solar Limit, is itself eclipsed by the Shat dow of the Earth at the Lunar Limit, when it is next at Full.
Euphrof. I understand you very well ; and I farther observe, that as the Nodes F and P are in opposite Points of the Orbit, so after half a Year, the Nodes will change their Nature, and that which is now the Solar Node wall then become the Lunar ; and the Lunar Node that now is, will then become the Solar Node, and will be the Season of Eclipses again.
Cleon. It will not be quite half a Year between, because the Sun, for Instance, may be eclipsed at the End of one Limit, as at G, (as in the Year 1732, December 6) and at the Beginning of the other at 0, (as May 2, 1733) in which Time there intervened not above 147 Days, which is short of half a Year by 35 Days. Yea, the Sun may leave one Limit, and arrive to the next in about four Months and an half, as in the Year 1740 the Sun was eclipsed Jan. 17, and again in June 12 ; and another Reason for this is, that the Nodes F and P are not fixed, but move in a retrograde Manner, so as that the distant Node is carried towards the Sun, and they meet near ten Days sooner than if the Node were fixed. VOL. I.
Euthrof. Well, I am not now so much at a Lofs to guess the reason why we have in different Years a different Number of Eclipses; why one Year four, another two, and a third Year five or fix; and allo the Reason why they happen at such and such Intervals and Seasons of the Year : This Doctrine of Nodes and Limits has given me the Rationale of Eclipses beyond whatever I expected; and now to be plain with you, I am got to a ne plus ultra, for I know not what further to ask or say on the Subject of Eclipses..
Cleon. We have pretty well exhausted the Subject, indeed, Euphrosyne, and I shall only observe to you next, that the Year 1740 had six Eclipses in a very peculiar Manner; for in those Years wherein fix Eclipses happen, there are generally two of the Sun and one of the Moon at each ecliptic Season; but in that Year there were three ecliptic Seasons, or the Luminaries came three Times within the ecliptic Limits, and each of them suffered an Eclipse each Time ; so that in that Year there were three Eclipses of the Sun, and three of the Moon; a Thing which very rarely happens. But Eclipses, like all other Things, in a long Course of Time, undergo a great Variety of Mutations and Changes, in the Circumstances we have now been considering.
Thus I've the Motions taught of Stars above,
Creech's Lucretius, Book V.
DIALOGUE VIII. Refieftions on the Immensity of the Universe, and of
the Plurality of Worlds.
Euphrosyne. THE Conversations whicñ have passed between us of
I late, have opened a new and strange Scene of Things to my Mind, and given quite a new turn to my
excedes ; they coulies of infinitq hrefhold of poet
Thoughts; I used to fancy the Earth on which we live, and ihe visible Lights of Heaven, were all the Creation, the whole of the Universe; nor did I ever imagine God had more than once said, Let us make Man, I thought we had held the second Class of created Beings, and must acknowledge Superiority only to Angels. But what can we think of ourselves, Cleonicus, if every Planet be a World, and every Star the central Sun of a System? If every System be inhabited, and those Inhabitants various as the Globes they live on!
Cleonicus. We can't certainly tell what to think, my Euphrosyne ; the Idea is too grand for human Comprehension; even Reason, Nature, and Analogy here are but blind Guides; they conduct us with Certainty but a little Way in the Abftrufities of infinite Creation; and ere we have passed, as it were, the Threshold of the Universe, we are loft and confounded. With the Poet we may lay
Now had th' eternal Architect fupreme,
Universal Beauty. Euphrof. The Poet's Refections are certainly just; they do indeed inspire us with noble and august Sentiments of the divine Being : He has made, and by his Providence governs, not one, but an Infinity of Worlds! How narrow must their Conceptions be, who imagine our Earth contains the Whole of the rational Species, or that Heaven is to be replenished with Colonies from this little Spot alone!
Cleon. Very true, Sister ; our Earth's a little Spot indeed, and inconsiderable in Comparison of the more noble Parts of this, much more of those of innumerable other Systems. In Regard of which, Mr. Baker thus expoftulates with opinionated Man.
What is this Earth, of which thou art so proud ?
And Mall, when it's no more, to endless Ages run. Euphrof. Our Earth to be sure can be considerable to no Part of the Universe but ourselves, and perhaps to the Inhabitants of the Moon, who behold it as a very large and bright Moon; but as to all other Worlds, Mercury, Venus, and Vars excepted, the Existence of our Earth (I find by what you have said) is neither known or sufpected by them: And if the Earth be not, then surely its Inhabitants must be absolutely unknown, and inconsiderable with Respect to the Universe.
Cleon. Your Observation is very just, Euphrosyne ; and yet you see what an high Value Mankind are apt to put upon themselves. Because we are superior to Brutes, we imagine we are next to Angels in the Scale of Beings : Because we have Dominion over the Fowls of the Heavens, and Beasts of the Earth, we invade the Stars; and claim a Sovereignty over over all the celestial Worlds, because this terrestrial Spot is put under our Feet. But how absurd, how ridiculous is our Vanity, in thinking all Things made for our Use, when the utmoft Ure we make of any Thing about us is but very trifling : Of all the numberless Species of Anirals, how few do we know ? how few do we use ? how many do we fear? how many do we Ay from? Again, do we boast the Use of the Sun? so may the most contemptible Infect: Does the Moon light up the Night for us so it does for the Owls, &c. allo. If all the Planets of our System were annihilated, few besides Astronomers would miss them. Lastly, who is the Man that can say any one fingle Circumstance of his Life was ever affected or altered by any one, yea, all of the fixed Stars? The Pride, therefore, and Arrogance of Man in challenging to himself the Empire of the Universe, are handsomely lached by the Satire and Irony of the following Verses.
now ? herless Species ut us is but vene utmost Unking