cannot be depended upon to do; well therefore might Mr. Maskelyne admit that my Invention would become of considerable value, even if taken in aid of the Lunar tables. I leave the reader to judge of the practicability of making these observations from what follows:
To ascertain the Longitude by the Moon and a star, requires a distinct horizon to be seen in the night, which is next to impossible, and if you have not an horizon, the altitude of neither Moon nor star can be taken: it also requires (and this perhaps when a ship is in a high sea) the distance of the Moon and star, in order to come at which, the image of one of them must be reflected through a silvered glass, and the other seen through an unsilvered part of the same glass; and they must be brought into conjunction in the line that connects the silvered and unsilvered parts, and this to an exactness only true in theory, for an error of a minute of a degree committed in this observation, will mislead the mariner half a degree in his Longitude; now I call upon any Astronomers of reputation publicly to declare, that they have, even at
solely and unreservedly on Lunar observations for the safety of his ship, would not the propounder of so hopeful a plan have reason to recollect a couplet (in the tale about a Squire swallowing a Cobbler) with which many of us were familiar in by-gone days: viz.
The Doctor having heard the case,
Burst into laughter in his face.
