The British Parliament voted a remarkable law in 1714. The need to avoid catastrophes and reduce the huge financial losses suffered by merchant shipping companies became so urgent that on 8 July 1714 the British Parliament passed the Longitude Act. The government offered a prize of £ 20,000 for a way of finding a ship's longitude to within half a degree, or about 50 kilometres. One man who rose to the challenge was an unassuming Yorkshire clockmaker. ... John Harrison's solution was to build a sea clock, or 'chronometer'. Possessing such a device, a mariner could, in Sobel's words, 'carry the true time from a home port, like an eternal flame, to any corner of the world'. To calculate his longitude at sea, he need only compare the chronometer's time with local time; if for instance, the Sun rose an hour earlier than at the port, then the ship must have sailed 1/24 of the way round the Earth, or about 1700 kilometres.