Page:The American Cyclopædia (1879) Volume IV.djvu/708

 696 CLOCKS AND WATCHES by weights were in use in the monasteries of Europe in the llth century. The Catholic clergy are credited with the introduction of clocks into England. They possessed much wealth, and had leisure to cultivate many of the arts, and were probably led to the cultiva- tion of horology from the desirableness of having some means of regulating their religious services. The first Westminster clock is said to have been erected from the proceeds of a fine which was imposed upon a chief justice of the king's bench about 1290. The Exeter cathedral clock, the striking part of which is said to be still in use, was constructed before 1317, and one was made by Wallingford in 1326. The cathedral clocks of Wells, Canter- bury, and Peterborough were also made about FIG. 1. Tick's Clock. that time. The first clock on record which approached in accuracy of movement the clocks of the present time was constructed for Charles V. of France by Henry Vick, in 1370. In fig. 1, representing this clock, the weight is suspended by a cord wound round the barrel ft, which carries a ratchet d. This ratchet, acting upon the great wheel c in one direction, will cause it to be driven by the weight. The great wheel c drives the pinion e, upon whose arbor or shaft is placed the wheel f. This again drives the pinion ', upon whose arbor is placed the crown wheel j, which in this clock forms the scape wheel, the action and office of which in the regulation of time will be de- scribed further on. This scape wheel, constant- ly moving in one direction, gives an impulse to the pallets or levers 1 1, whenever they are brought within the range of its teeth ; and this they are made to do by the backward and for- ward vibrations of the weighted balance m m, suspended by the cord n. These vibrations, caused by the action of the teeth in the scape wheel upon the pallets, being isochronous, or nearly so, divide the time of the successive escaping of the teeth of the crown wheel into equal parts. This balance was indeed a rudi- mentary balance wheel ; a rim added, making it the diameter of a circle, and a hair spring in place of the cord, would have made it one. The turning of the single hand once around in 12 hours was accomplished by hav- ing the arbor of the barrel pass through the front plate p. A pinion upon this arbor, which turns once in an hour, pitches into the large wheel 0, which has 12 times as many teeth as the pinion has leaves, and which will therefore revolve once in 12 hours. The ap- pliance for winding consists of the pinion h at the lower part of the clock, which is made to turn the wheel g by means of an arbor which passes through the face of the clock, and which is squared to fit a key. The contrivance for regulating the motion of the last wheel is called the escapement, and the wheel is called the scape wheel, whether of the modern form or the old-fashioned crown wheel of Vick, used for nearly three centuries after in clocks, and for a much longer time in watches. It is the most essential part of the timepiece ; and upon its adjustment, after the application of the pendulum, nearly all the study relating to the subject of horology has been expended. It is called the escapement, because each tooth of the scape wheel is allowed to escape from cer- tain arms of the pendulum called pallets, after having been arrested during a period of time. But the performance of this clock must have been quite imperfect, although it was a marvel of mechanism in its day. It needed an escape- ment capable of making a more accurate divi- sion of time. It was impossible at that time, although it has since been accomplished, to cause the balance to oscillate in exactly equal spaces of time. The first instrument used for this purpose was the pendulum, which it can scarcely be doubted was employed in the early ages to measure small periods of time by simply counting its vibrations, without connecting it with mechanism. It is said that the ancient astronomers measured the duration of eclipses with it, but there is no recorded proof of its use before the discovery of Galileo at Florence in 1582, by observations upon a swinging chandelier, that a pendulum vibrated in arcs of different lengths in the same time, if the arcs were small. It has been said that a pendulum clock was made for St. Paul's church in Covent Garden by Harris, a London clockmaker, in 1642 ; but this must be an error, or the contro- versy could never have taken place between Dr. Hooke and Huygens, who is now univer-