1693-1776 astronomicalclock astronomicalclocks biografi biographie biography chronometer chronometers chronomètre clockandwatchmakers clocksandwatchmakers geografischelengte geografischelänge geography gmt harrison harrisontimekeepers histoire history horlogemakers horology john largetypebooks literatureinitalian longitude longnowmanualforcivilization lunardistancemethod lunartables measurement messung navigasjon navigatie nonfiction research royalsociety scheepvaart schiffschronometer science sterrenkunde