“322. It is particularly to be noted, that Eclipses which have happened many centuries ago, will not be found by our present Tables to agree exactly with antient observations, by reason of the great Anomalies in the lunar motions; which appears an incontestable demonstration of the non-eternity of the Universe. For it seems confirmed by undeniable proofs, that the Moon now finishes her period in less time than formerly, and will continue by the centripetal law to approach nearer and nearer the Earth, and to go sooner and sooner round it: nor will the centrifugal power be sufficient to compensate the different gravitations of such an assemblage of bodies as constitute the solar system, which would come to ruin of itself, without some new regulation and adjustment of their original motions[[68]].
Thales’s Eclipse.
“323. We are credibly informed from the testimony of the antients, that there was a total Eclipse of the Sun predicted by Thales to happen in the fourth year of the 48th [[69]]Olympiad, either at Sardis or Miletus in Asia, where Thales then resided. That year corresponds to the 585th year before Christ; when accordingly there happened a very signal Eclipse of the Sun, on the 28th of May, answering to the present 10th of that month[[70]], central through North America, the south parts of France, Italy, &c. as far as Athens, or the Isles in the Ægean Sea; which is the farthest that even the Caroline Tables carry it; and consequently make it invisible to any part of Asia, in the total character; though I have good reasons to believe that it extended to Babylon, and went down central over that city. We are not however to imagine, that it was set before it past Sardis and the Asiatic towns, where the predictor lived; because an invisible Eclipse could have been of no service to demonstrate his ability in Astronomical Sciences to his countrymen, as it could give no proof of its reality.
Thucydides’s Eclipse.
“324. For a farther illustration, Thucydides relates, that a solar Eclipse happened on a Summer’s day in the afternoon, in the first year of the Peloponnesian war, so great that the Stars appeared. Rhodius was victor in the Olympic games the fourth year of the said war, being also the fourth of the 87th Olympiad, on the 428th year before Christ. So that the Eclipse must have happened in the 431st year before Christ; and by computation it appears, that on the 3d of August there was a signal Eclipse which would have past over Athens, central about 6 in the evening, but which our present Tables bring no farther than the antient Syrtes on the African coast, above 400 miles from Athens; which suffering in that case but 9 Digits, could by no means exhibit the remarkable darkness recited by this historian; the center therefore seems to have past Athens about 6 in the evening, and probably might go down about Jerusalem, or near it, contrary to the construction of the present Tables. I have only obviated these things by way of caution to the present Astronomers, in re-computing antient Eclipses; and refer them to examine the Eclipse of Nicias, so fatal to the Athenian fleet[[71]]; that which overthrew the Macedonian Army[[72]] &c.” So far Mr. Smith.
The number of Eclipses.
325. In any year, the number of Eclipses of both Luminaries cannot be less than two, nor more than seven; the most usual number is four, and it is very rare to have more than six. For the Sun passes by both the Nodes but once a year, unless he passes by one of them in the beginning of the year; and if he does, he will pass by the same Node again a little before the year be finished; because, as these points move 19 degrees backward every year, the Sun will come to either of them 173 days after the other § [319]. And when either Node is within 17 degrees of the Sun at the time of New Moon, the Sun will be eclipsed. At the subsequent opposition the Moon will be eclipsed in the other Node; and come round to the next conjunction again ere the former Node be 17 degrees past the Sun, and will therefore eclipse him again. When three Eclipses fall about either Node, the like number generally falls about the opposite; as the Sun comes to it in 173 days afterward: and six Lunations contain but four days more. Thus, there may be two Eclipses of the Sun and one of the Moon about each of her Nodes. But when the Moon changes in either of the Nodes, she cannot be near enough the other Node at the next Full to be eclipsed; and in six lunar months afterward she will change near the other Node: in these cases there can be but two Eclipses in a year, and they are both of the Sun.
Two periods of Eclipses.
326. A longer, and consequently more exact period than the above-mentioned § [320], for comparing and examining Eclipses which happen at long intervals of time, is 57 Julian years 324 days 21 hours 41 minutes and 35 seconds; in which time there are just 716 mean Lunations, and the Sun is again within 5 minutes of the same Node as before. But a still better period is 557 years 21 days 18 hours 30 minutes 12 seconds; in which time there are 6890 mean Lunations; and the Sun and Node meet again so nearly as to be but 11 seconds distant.
An account of the following catalogue of Eclipses.