CLOCK AND WATCH MAKING. The first author who has introduced the term here. logiunt as applicable to a clock that struck the hours appears to be Dante, who was born in 1265 and died in 1321. It would appear from this, that striking clocks were known in Italy as early as the latter part of the thirteenth or beginning of the fourteenth century. There is known to have been some such kind of clock at quite as early a period in England ; but it is considered probable that the next fol lowing century produced the first clock pro perly so called, the term horologiunt having previously included many kind of time mea surers. Many allusions to celebrated clocks, in France, Italy, Germany, and Holland, are to be met with, belonging to the fourteenth and fifteenth centuries. It is now believed that a regulated clock was not the invention of one man, but a compound of successive inventions, each worthy of a separate con triver.
There was a clock made in 1361 by De Wyck, for the Emperor of Germany, which had two pallets worked by a crown-wheel, and two weights on a lever to regulate the move ment to time. In 1481 Walthus made a ba lance-clock for astronomical observations. In 1560 Tycho Brahe had four clocks which in dicated hours, minutes, and seconds ; the largest of which had only three wheels, one having 1200 teeth. In 1577 Moestlin had a Hock whose beats enabled him to determine approximately the apparent diameter of the sun. At what time watches or small clocks were introduced, by the use of a mainspring nstead of a weight as the moving power, is not known ; but it is supposed to have been in lie early part of the sixteenth century. Gall ee's discovery of the isochronism of the pen iulum paved the way for the introduction of )endulurn clocks ; and it is probable that both 3alileo and Huyghens had constructed pen lulum clocks before 1618, though some writers ;ay that Richard Harris made a pendulum dock a few years earlier, viz. in 1611. In 1676 3arlow, a London clock-maker, invented the •epeating mechanism by which the hour last ;truck may be known by pulling a string. Se
'eral artists followed in the same line, parti :ularly Quare, in London, and Julien le Roy, Largay, Thiout, &c., on the Continent.
Clocks were soon after this made to show no only mean but apparent time.
A London clockmaker named Clement in vented in 1680 the anchor-escapement, whirl was a great improvement on the crown-whee before in use; he also introduced the practice o suspending the pendulum by a thin and flex" ble spring. The next important improvemen was the adjustment of the length of the pendu lum to the varied effects of heat and cold. 1n1711 George Graham, by substituting a jar of mar cury for the pendulum-ball, succeeded in re taining the point of suspension and the centre of oscillation at the same distance from cacl other., The principal objection to this pendu. Inm is its liability to breakage, of which its author felt the full force, and in consequence suggested the idea of the opposite expansions of different metals as a compensation for a pendulum. John Harrison immediately turned his attention to the subject, and, by dint ol perseverance, overcoming all the difficulties ol his humble and retired situation, not only as tonished the world by his improvements in horological machines, but absolutely construe ted'with his own hands a timekeeper which determined the longitude within such limits as to procure him the parliamentary reward of 20,000/. Although the anchor escapement previously mentioned was a great improvement upon all that had preceded it, still it was sub ject to objections, not one of the least of which was that at evert' vibration a considerable re coil took place. The inconveniences of this escapement were however removed (about the same time with the invention of Harrison's pendulum) by Graham, who introduced what is called the dead-beat escapement, which is both simple and effective.