176 Ot THE LATITUDE AND LONGITUDE.

find what time it is at Greenwich when themoon and star have the fame distance; and thistime, being compared with the time of observa-tion, will, by allowing 15 degrees to an hour,give the longitude of the place required.

The names and places of the brightest fixedstars, are to be found in the " Tables requisite tobe used with the Nautical Almanac,” togetherwith the methods made use of for obtainingtheir true distances from the moon at the timeof observation. For it is to be noted, that thedistance found by the quadrant, is not that whichis to be used in determining the longitude, butthe distance as it would appear to a spectatorplaced at the earth’s center. This is the distanceas it is computed for Greenwich; and in orderthat they may agree, it must be determined inthe same manner for the place of observation.The necessity of these operations, will be suffici-ently obvious from the consideration of theearth’s being a globe; but as the calculationsupon which they depend, are deduced from theprinciples of spherical trigonometry, they canonly be understood by those who have a know-ledge of that subject.

This last method of finding the longitude,which is founded upon observations of the moon,is, by the general consent of astronomers, the bestthat has yet been discovered. And though it maypot be easily practised by every common mariner,

yet