2z3

*fhe Calculation of mean New and Füll Moons.

weight at the end of the line hanging freely in a pail os water placedbelow it on the floor.—But because this may not be quite correct forthe first time, on account that the plummet will not fettle immediately,even in water; it may be farther corrected on the following days, bythe above method, with the sun and dock ; and so brought to a verygreat exactness.

N. B. The rays tranfmitted through the hole, will cast but a faintimage of the fun, even on a white fcreen, unlefs the room be fo dark-ened that no sun-fhine may be allowed to en ter, but what comesthrough the fmall hole in the piate. And always, for forne time beforethe obfervation is made, the plummet ought to be immersed in a jarof water, where it may hang freely; by which means the line willfoon become steady, which otherwise would be apt to continue swing-ing-

As this meridian line will not only be sufficient for regulating ofclocks and watches to the true time by equation tabi es, but also formof l astronomical purposes, 1 (ha.ll say nothing of the magnificent andexpensive meridian lines at Bologna and Rome, nor of the better me-thods by which astronomers obferve precisely the tranfits of the hea*venly bodies on the meridian.

L E C T. XII.

Shewing how to calculate the mean time of any new or füllmoon , or eclipfe , from the creation of the world to theyear of CHRIST 5800.

I N the following tables, the mean Iunation is about a 2oth part of asecond of time longer than its measure as now printed in the thirdedition of my Astronomyj which makes a difference of an hour andzo minutes in8oooyears.—But this is not material, when only the meantimes are required.

PRECEPTS.

To find the mean time of any new or füll moon in any given year andmonth aster the Christian /Era.

1. If the given year be found in the second column of the Table ofthe moon'& mean motion from the fun , under the title Year i before and asterCHRIST ; write out that year, with the mean motions belonging to2 it,