About 1500 Peter Hele of Nuremberg invented the _mainspring_ as a substitute for the weight, and the _watch_ appeared soon afterwards (1525 A.D.). The pendulum was first adopted for controlling the motion of the wheels by Christian Huygens, a distinguished Dutch mechanician, in 1659. To Thomas Tompion, "the father of English watchmaking," is ascribed the honour of first fitting a _hairspring_ to the escapement of a watch, in or about the year 1660. He also introduced the _cylinder escapement_ now so commonly used in cheap watches. Though many improvements have been made since his time, Tompion manufactured clocks and watches which were excellent timekeepers, and as a reward for the benefits conferred on his fellows during his lifetime, he was, after death, granted the exceptional honour of a resting-place in Westminster Abbey. THE CONSTRUCTION OF TIMEPIECES. A clock or watch contains three main elements:--(1) The source of power, which may be a weight or a spring; (2) the train of wheels operated by the driving force; (3) the agent for controlling the movements of the train--this in large clocks is usually a pendulum, in small clocks and watches a hairspring balance. To these may be added, in the case of clocks, the apparatus for striking the hour. THE DRIVING POWER. _Weights_ are used only in large clocks, such as one finds in halls, towers, and observatories. The great advantage of employing weights is that a constant driving power is exerted. _Springs_ occupy much less room than weights, and are indispensable for portable timepieces. The employment of them caused trouble to early experimenters on account of the decrease in power which necessarily accompanies the uncoiling of a wound-up spring. Jacob Zech of Prague overcame the difficulty in 1525 by the invention of the _fusee_, a kind of conical pulley interposed between the barrel, or circular drum containing the mainspring, and the train of wheels which the spring has to drive. The principle of the "drum and fusee" action will be understood from Fig. 201. The mainspring is a long steel ribbon fixed at one end to an arbor (the watchmaker's name for a spindle or axle), round which it is tightly wound. The arbor and spring are inserted in the barrel. The arbor is prevented from turning by a ratchet, B, and click, and therefore the spring in its effort to uncoil causes the barrel to rotate. [Illustration: FIG. 201.]