[LONGITUDE]. PLANK, STEPHEN. An Introduction To a true Method For the Discovery of Longitude at Sea. London, 1720. Small 8vo, later plain wrappers--ROUBAIS DU TOURCOIN, JACQUES DE. A Physical Dissertation Concerning...Longitude...Tranlsated into English. London, 1721. Small 8vo, disbound. Babson Newton 106. (2)