At the time, it had long been possible to sail to most parts of the world and expect to return safely, but an accurate means of measuring longitude would allow for more speed and less risk and vastly enhance opportunities for long-distance trade. Coupled with frequent large-scale maritime losses from navigational errors, this situation made some kind of initiative inevitable.
The likely methods and familiar problems were neatly summarised by Isaac Newton. Longitude at sea could be calculated with an accurate timepiece, which shipboard motion and variations of heat and cold had thus far made impossible; by monitoring Jupiter’s satellites, which the size of the telescopes required rendered impracticable; by the location of the moon, which only provided accuracy up to three degrees; and by ‘Mr Ditton’s project’, which involved having moored vessels fire shells 6,440 feet into the air at set times, allowing other ships to take bearings – an idea that caused hilarity at the time, although it seems ingenious enough.
Thanks to Dava Sobel’s Longitude, the story of how Lincolnshire clockmaker John Harrison adapted his gridiron-pendulum clock for use at sea is well known. Here, that story is set in a broader context accompanied by illustrations from contemporary artists and photographs of the magnificent array of chronometers that the search for longitude produced. Published to coincide with a major exhibition at the National Maritime Museum, it’s the story of how we found our place in the world.
FINDING LONGITUDE: How Ships, Clocks and Stars Helped Solve the Longitude Problem by Richard Dunn and Rebekah Higgitt, Collins and Royal Museums Greenwich, £25