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