These things being properly considered, it will not be difficult to conceive how astronomers are able to foretell the exact time when any phenomenon of this kind will happen; for, as an eclipse can only take place at the time of a new or full moon, the principal requisites are, to determine the number of mean conjunctions and oppositions that will happen every year, and the true places of the sun and moon in their orbits at each of those times. And, if from this, when proper calculations have been made, it appears that the two luminaries are within the proper limits of the node, there will be an eclipse. To facilitate these operations, we have astronomical tables ready computed, by which the places of the heavenly bodies, and every other particular required, may be easily found for any given instant of time.[124] With delight we reflect on the invaluable benefits which this _lesser light_ confers on our globe. She sometimes appears visible in the presence of the sun; but how faint and pale is her shining! God has appointed her to _rule the night_, and give light to men. How cheerless and uncomfortable would our nights be, were we destitute of the light which this faithful and inseparable companion of our earth dispenses! How strange are her eclipses, occasioned by the earth interposing and shading her face! but, they are highly useful in astronomical, geographical, and chronological calculations. How salutary, too, is her attractive influence, which sways the ocean, and actuates the world of waters; causing the swelling of the tides, and perpetuating the regular returns of ebb and flow; by which the liquid element itself is preserved from putrefaction, and the surrounding continents from infection and disease. A moonlight night has led the greatest poets in every age to vie with each other in attempting to describe its beauty and use. Among all the treasures of modern poetry, I know not one superior, for pleasing imagery, and variety of numbers, to that of Milton: “Now came still evening on, and twilight grey Had in her sober livery all things clad. Now glowed the firmament With living sapphires: Hesperus, that led The starry host, rode brightest, till the Moon, Rising in clouded majesty, at length, Apparent queen, unveiled her peerless light. And o’er the dark her silver mantle threw.” Homer, in the eighth book of the Iliad, gives us a description of a fine moonlight night, which is esteemed a master-piece of nocturnal painting. Milton’s pencil leaves off where that of Homer begins: