The next development in accuracy occurred after 1656 with the invention of the pendulum clock Galileo had the idea to use a swinging bob to regulate the motion of a time telling device earlier in the 17th century Christiaan Huygens, however, is usually credited as the inventor He determined the mathematical formula that related pendulum length to time (99.38 cm or 39.13 inches for the one second movement) and had the first pendulum-driven clock made In 1670, the English clockmaker William Clement created the anchor escapement, an improvement over Huygens' crown escapement Within just one generation, minute hands and then second hands were added. A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation The position of a ship at sea could be determined with reasonable accuracy if a navigator could refer to a clock that lost or gained less than about 10 seconds per day This clock could not contain a pendulum, which would be virtually useless on a rocking ship Many European governments offered a large prize for anyone that could determine longitude accurately; for example, Great Britain offered 20,000 pounds, equivalent to millions of dollars today The reward was eventually claimed in 1761 by John Harrison, who dedicated his life to improving the accuracy of his clocks His H5 clock was in error by less than 5 seconds over 10 weeks.[27] The excitement over the pendulum clock had attracted the attention of designers resulting in a proliferation of clock forms Notably, the longcase clock (also known as the grandfather clock) was created to house the pendulum and works The English clockmaker William Clement is also credited with developing this form in 1670 or 1671 It was also at this time that clock cases began to be made of wood and clock faces to utilize enamel as well as hand-painted ceramics. French decimal clock from the time of the French Revolution On November 17, 1797, Eli Terry received his first patent for a clock Terry is known as the founder of the American clock-making industry. Alexander Bain, Scottish clockmaker, patented the electric clock in 1840
