351. In Astronomy, Eclipses of the Moon are of great use for ascertaining the periods of her motions; especially such Eclipses as are observed to be alike in all circumstances, and have long intervals of time between them. In Geography, the Longitudes of places are found by Eclipses, as already shewn in the eleventh chapter: but for this purpose Eclipses of the Moon are more useful than those of the Sun, because they are more frequently visible, and the same lunar Eclipse is of equal largeness and duration at all places where it is seen. In Chronology, both solar and lunar Eclipses serve to determine exactly the time of any past event: for there are so many particulars observable in every Eclipse, with respect to its quantity, the places where it is visible (if of the Sun) and the time of the day or night; that ’tis impossible there can be two Eclipses in the course of many ages which are alike in all circumstances. [Sidenote: The darkness at our SAVIOUR’s crucifixion supernatural.] 352. From the above explanation of the doctrine of Eclipses it is evident, that the darkness at our SAVIOUR’s crucifixion was supernatural. For he suffered on the next day after eating his last Passover-Supper, on which day it was impossible that the Moon’s shadow could fall on the Earth, for the _Jews_ kept the Passover at the time of Full Moon: nor does the darkness in total Eclipses of the Sun last four minutes in any place § 333, whereas the darkness at the crucifixion lasted three hours, _Matt._ xxviii. 15. and overspread at least all the land of _Judea_. CHAP. XIX. _The Calculation of New and Full Moons and Eclipses. The geometrical Construction of Solar and Lunar Eclipses. The examination of antient Eclipses._ 353. To construct an Eclipse of the Sun, we must collect these ten Elements or Requisites from the following Astronomical Tables. [Sidenote: Requisites for a solar Eclipse.] I. The true time of conjunction of the Sun and Moon: to know at what conjunctions the Sun must be eclipsed; and to the times of those conjunctions, II. The Moon’s horizontal parallax, or angle which the semi-diameter of the Earth subtends as seen from the Moon. III. The Sun’s true place, and distance from the solstitial colure to which he is then nearest, either in coming to it or going from it. IV. The Sun’s declination. V. The angle of the Moon’s visible path with the Ecliptic. VI. The Moon’s Latitude or Declination from the Ecliptic. VII. The Moon’s true hourly motion from the Sun. VIII. The Angle of the Sun’s semi-diameter as seen from the Earth. IX. The Angle of the Moon’s semi-diameter as seen from the Earth. X. The semi-diameter of the Penumbra. And for an Eclipse of the Moon, the following Elements. [Sidenote: Requisites for a lunar Eclipse.] I. The true time of opposition of the Sun and Moon; and for that time, II. The Moon’s horizontal parallax. III. The Sun’s semi-diameter.