A letter of advice to all the worthy and ingenuous merchants of the city of London, and elsewhere in England, ... And to all ... ingenious artists in astronomy, geography and navigation; shewing an exact, ... way to know the longitude of all places in the world, ... and also how the longitude of places may be better known upon ship-board. - Bull, Digby. (printed for the author, and are to be sold by John Morphew,, 1706)