Shortt ClocksThe Shortt Clock is named after William Hamilton Shortt who invented it early in the 20th century. It reached an accuracy of a second or two a year. As such it was the most accurate of all mechanical clocks and remained the pinnacle of clock accuracy until the development of quartz in the 1930s. What Is A Shortt Clock?The Shortt Clock is a variation of the traditional pendulum clock with two pendulums. Although it uses electricity it is classed as a mechanical clock because the electricity is not used to to keep time. Free PendulumsIn theory, a free swinging pendulum will keep acurate time. However in reality pendulum mechanisms were never completely free swinging. As well as keeping time, the pendulum also interacts with the escapement and hence the main clock driving mechanism. As well as keeping time it is also doing work and this introduces inaccuracies into the swing of the pendulum. There are also atmospheric and temperature variations that can affect the duration of the pendulum swing. The ideal free swinging pendulum simply didn't exist. Many people worked on the problem of free pendulums. Towards the end of the 19th century a number of "nearly free" pendulum clocks were developed and ideas from these led eventually to the invention of the Shortt Clock, derived most directly from the Frank Hope-Jones Synchronome. Double PendulumsIn the Shortt clock, there are two separate pendulums. The timekeeping pendulum is simply that, a timekeeper. It does no work. The clock mechanism is controlled by a second pendulum which is keept synchronised with the master pendulum electrically. It's important to note that the timekeeping is all done by the mechanical, gravity driven pendulum - hence the Shortt clock remains a mechanical timekeeper despite the use of electricity. The master timekeeping pendulum is kept as free as possible by being enclosed in a sealed, part vacuum tube fixed to a wall. This master pendulum then signals electrically to a slave pendulum which in turn does the actual work of controlling the clock. This ingenious combinaton of mechanical free pendulum timekeeping with electrical power was the ultimate mechanical clock. Indeed, it was the Shortt clock that first proved the Earth itself is a far from perfect timekeeper. It could be argued that the Shortt Clock was the first clock more accurate than nature.
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发表于 2008-2-26 23:10:00
