The description and use of a new astronomical instrument, for taking altitudes of the sun and stars at sea, without an horizon ; together with an easy and sure method of observing the eclipses of Jupiter's satellites, or any other phoenomenon of the like kind, on ship-board ; in order to dtermine the difference of meridians at sea. . To which are added, tables for computing the times when the eclipses of the first satellite of Jupiter happen under the meridian of London