Proposal for a new method of determining the longitude, by an absolute altitude of the moon

Abstract The method employed by the author for determining the longitude by the observation of an absolute altitude of the moon, was pro­posed, many years ago by Pingré and Lemmonier; and the princi­pal difficulty which stood in the way of its adoption, was its re­quiring the exact determination of the moon’s declination reduced to the place of observation. This difficulty the author professes to have removed by supposing two meridians for which the altitudes are to be calculated: and the only remaining requisite is the accu­rate determination of the latitude, which presents no great difficulty, either on land or at sea. Examples are given of the practical work­ing of this method; showing that if the latitude of a place of obser­vation be obtained within a few seconds, the longitude will be found by means of a single observation of the altitude of the moon.