A supplement to the treatise for finding the longitude. [electronic resource] : Containing all the requisites for the ready computing and obtaining the longitude of a ship or place, by observations of the sun and moon. (The tables of the requisites are for the year 1764.) To which are added, tables of the declination of the sun, and of the variations of the declinations, &c. whereby the true declination of the sun may be had at any given time for a century to come. Also, the most practical method of obtaining the variation of the compass, or magnetic needle. By Robert Waddington, teacher of the mathematicks, in Three Tun Court, Miles's Lane, Cannon-street, London.