Zy6 OF THE ECLIPSES, &C.

eclipse, or otherwise not, agreeable to what hasbeen already observed upon this subject:.

*■ But in order to facilitate these operations, wehave astronomical tables ready computed fromthe theory of gravitat on, by which the placesof the heavenly bodies, and every other necessaryparticular, may be easily found for any giveninstant of time. Dr. Id alley has also given acatalogue of all the eclipses hat took place fromthe year 1701 to 1718, which the author of L’Artde verifier les Dates, and others, have continuedup to the year 1800; so that by means of theperiod of eighteen years, in which there is foundto be nearly a regular return of the fame eclipses,it is easy to institute a calculation, that will de-termine, to a great degree of precision, the timesin which they will happen.

This method, however, is not strictly scien-tific ; and there are, besides, many other ele-ments employed in calculating the quantity andduration of eclipses, which, as you are unac-quainted with the higher parts of mathematics,it is scarcely possible to explain in a clear andsatisfactory manner. If what has been saidshould lead you to wissi for a farther acquaint-ance with this doctrine, you will find it amplytreated of by M. de la Lande, Dr. Long, andothers; but these authors cannot be read, to anyadvantage, till you have obtained a previousknowledge of many other branches of science.

LET-