The Probert Encyclopaedia of General Information

CLOCK

A clock is an instrument for measuring time and indicating hours, minutes, and usually seconds, by means of hands moving on a dial-plate, and traditionally differing from a watch mainly in having the movement of its machinery regulated by a pendulum, and in not being portable. A clock also chimes, though the term clock is frequently, and incorrectly, applied to the non-chiming instruments for measuring time, which are technically known as a timepiece.

The use of a horologium, or hour-teller, was common even amongst the ancients, but their time-pieces were nothing else than sun-dials, hour-glasses, and clepsydrae. In the earlier half of our era we have accounts of several attempts at clock construction : that of Boethius in the 6th century, the clock sent by Harun al Rashid to Charlemagne in 809, that made by Pacificus, archdeacon of Verona, in the 9th century, and that of Pope Sylvester II in the 10th century. It is doubtful, however, if any of these was a wheel-and-weight clock, and it is probably to the monks that we owe the invention of clocks set in motion by wheels and weights. In the 12th century clocks were made use of in the monasteries, which announced the end of every hour by the sound of a bell put in motion by means of wheels. From this time forward the expression, 'the clock has struck,' is often met with. The hand for marking the time is also made mention of.

In the 14th century there are stronger traces of the later system of clock-work. Dante particularly mentions clocks. Richard, abbot of St Albans in England, made a clock in 1326, such as had never been heard of until then. It not only indicated the course of the sun and moon, but also the ebb and flood tide. Large clocks on steeples likewise were first made use of in the 14th century. Watches are a much later invention, although they have likewise been said to have been invented as early as the 14th century. A celebrated clock, the construction of which is well known, was set up in Paris for Charles V in 1379, the maker being Henry de Vick, a German. It probably formed a model on which clocks were constructed for nearly 300 years, and until Huyghens applied the pendulum to clock-work as the regulating power, about 1657. The great advantage of the pendulum prior to the invention of electronic oscillators is that the beats or oscillations of a pendulum all occupy substantially the same time (the time depending on its length), hence its utility in imparting regularity to a time-measurer. The mechanism by which comparative regularity was previously attained, though ingenious and simple, was far less perfect; and the first pendulum escapement that is, the contrivance by which the pendulum was connected with the clock-work, was also less perfect than others subsequently introduced, especially Graham's dead-heat escapement, invented in 1700.

In a watch, prior to the invention of electronics, the balance-wheel and spring served the same purpose as the pendulum, and the honour of being the inventor of the balance-spring was contested between Huyghens and the English pliilosopher Dr. Hooke. Various improvements followed, such as the chronometer escapement, and the addition of a compensation adjustment, by which two metals having unequal rates of expansion and contraction under variations of temperature are combined in the pendulum or the balance-wheel, so that, each metal counteracting the other, the vibrations are isochronous under any change of temperature. This arrangement was perfected by Harrison in 1726, and was especially useful in navigation.
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