the whole twenty-nine days, twelve hours, and forty-four minutes, which is termed a fynodical month.

I believe, having got these bodies in a straight line, I may as well explain the nature of ECLIPSES. I faid lately that the earth has a course of her own; fhe being the primary planet, I muft no doubt confider her courfe as the original, and obferve, that the line defcribed by the moon in her revolution, does not always agree with the line of the earth's motion; it is not, I fay, in the fame plane, but is fometimes higher, fometimes lower; fo that it agrees with it only now and then, but croffes it in certain parts in most of its revolutions. You fee therefore at once, that if it be higher than the plane of the earth's motion, when it is between that and the fun, it cannot intercept the light of the fun from the earth (which is what conftitutes an eclipfe of the fun); it cannot, I fay, prevent the earth from feeing the fun, for the earth fees under it or if, when between the fun and the earth, it be lower than the plane of the earth's motion, it equally avoids hindering our fight of the fun, for the earth fees over it: but when between the fun and the earth, the moon moves in that part of her orbit which coincides with the plane of the terrestrial motion, then the is bona fide interpofed between the fun and the earth, and in confequence, the beams of the fun intended for the earth are received by the moon, and the earth is deprived of them. This conftitutes a SOLAR eclipfe in other words, the fhadow of the moon falls upon the earth.

An

An eclipfe of the moon, it is evident, cannot happen in this quarter, for he has no light of which to be deprived, her unilluminated face being turned toward the earth; nor can it happen when the has performed a quarter of her course, for then she is not in a direct line with the fun and the earth; we must look for it therefore at the full, for there only the is liable to this event.

As the path of the moon is not always coincident with the orbit of the earth, fhe enjoys at this period much the fame advantages as the earth was before obferved to do; I mean, that when her courfe is higher than the earth's, she fees the fun by looking over the earth; and when her course is lower than the earth's, fhe fees the fun by looking under it: but when they coincide, the earth intercepts the light of the fun, and deprives her of those beams intended for her use; in confequence, having no light in herself, the refumes her natural darkness, and ceases to fhine, in fuch proportion, as the earth intercepts her light; or, in other words, as the shadow of the earth falls upon her.

Thefe, LADIES and GENTLEMEN, are the elements and principles of that phænomenon, which excites in the mind of ignorance fuch dread and terror, which has ever been regarded as an evil omen, has funk the hearts of the most valiant, and weakened the fpirits of the moft magnanimous ; yet nevertheless has fometimes produced the happiest effects; witnefs the celebrated eclipfe of the fun, foretold in the infancy of aftronomy by THALES the Ionian (anté A. D. 603), which happening during a battle between the armies

of Alyattes king of Lydia, and Cyaxares the Median, was regarded by both parties as an evil omen, fufpended the engagement, and concluded a peace.

Such a phænomenon, once generally dreaded, and dreaded ftill among the unenlightened nations of the earth, will this evening yield us rational entertainment; fuch is the difference between knowledge and ignorance, we look out for an eclipfe, and anticipate the fatisfaction, while the favage fhrinks from the awful fight, or clatters every inftrument capable of noise, that he may awaken the moon from her fwooning, or eafe her in her labour. The heathens of antiquity used to light up torches, to blow trumpets and horns, to rattle their veffels of brafs and iron; and after the eclipfe was over, proceffions and facrifices expreffed their joy at her deliverance. Our compaffion withholds the farcafm; " Lo! "these are the gods you worship;" while we cannot but regret the blindnefs of mankind, who adopted fuch impotent divinities, who after being fpectators of the entire paffivenefs, and utter inactivity of their fuppofed deities, yet called for help on gods unable to help themselves, and fought protection from gods on whom they alfo bestowed affiftance.

The advantages we enjoy in the science of the present day, may profitably engage your reflection while attending to an example of fuch a phænomenon; the moon now fhines full; but obferve, on her eastern limb there feems a flight deficiency of light; now it augments into a notch of dark; now the dark increases; the advances, you fee, into the fhadow of the earth, which now covers great part of her, now gradually

withdraws

withdraws to the other fide of the moon, now is fcarce ap parent even there, and now, having quitted the fhadow, the moon again thines with her former luftre.

Such, LADIES and GENTLEMEN, is the courfe of eclipses: they are greater or lefs, according as the moon enters more or lefs deeply into the fhadow of the earth, and its atmofphere, which, in current language, may pafs for one uniform fhadow. The time of the longest poffible duration of a total lunar eclipfe, is three hours, fifty-feven minutes; but a total lunar eclipse may be twenty minutes fhorter. The longest time of a total eclipfe of the fun (i. e. of total darkness) is about four minutes; and the time taken by the moon to cross the fun's body (ie. the duration of the eclipse), is, at her nearest access to the earth, about two hours and three quarters.

The moon fometimes in the middle of a total eclipfe is vifible in fome places, and invisible in others, according to the different conftitution of the air; but generally appears of a dusky, reddish, or copper-colour, efpecially towards the edges; this colour is owing to the folar rays refracted through the earth's atmosphere, and reaching the moon; the red rays being leaft refracted, they pafs through our atmosphere in the greatest quantity.

We noticed, when speaking of the fun, that although he is a globe, yet by reafon of his distance he appears flat; and the same we obferve of the moon; which, though unquef tionably a globe, yet presents a flat face (termed a Disk) to the spectator. The SURFACE of this face, even to the naked eye, appears rough, uneven, and replete with mountains and

caverns; and through a telescope we obferve very plainly the feparation between her enlightened and her dark parts, is broken by hills and valleys; in her lately enlightened parts, presenting many dark spots, while in her unenlighteħed parts, the tops of the mountains and eminences catch the first gleams of the folar rays, and are diftinctly feen to enlarge, and become brighter as the light rifes and fpreads upon them This very agreeable fight requires but an hour or two to complete it.

The mountains in the moon are thought to be higher than any we have on earth, and her caverns proportionally deep; which has given occafion to fome, to fuggeft that if she has any inhabitants, they may use them as cool retreats from the ardour of the fun, which cannot but be very great in the course of a day fo long as a fortnight is with us. For you will please to obferve, that during the courfe of the moon round the earth, the fun enlightens fucceffively every part of that globe; but only once; fo that she has but one day in all that time she revolving on her axis only once, confequently only once turning in fucceffion each part of her orb to the fun. Obferve too, that as fhe turns on her axis in the fame time as fhe goes round our earth, the fame part of her body is directed towards us, and we fee conftantly the fame afpect; except what little variation is occafioned by the different courfes of the two planets. To explain which, if we compare the face of the moon to a human face, we may fay, that we sometimes fee lefs of her right cheek, and more of her left; fometimes more of her right cheek, and lefs of her left; fome