Page:The New International Encyclopædia 1st ed. v. 05.djvu/59

* CLOCK. into the backward and forward motion." The accompanying sketch of Dc Vick's clock is use- ful not only from its historical interest, but also because, from its comparative simplicity, it will form a groundwork for further explanation of the mechanism of clocks in their more compli- cated form. It w ill he readily understood, from a glance at the annexed figure (Fig. 1), that as the weight A tends to uncoil tlic cord and set in motion the cylinder B round its axis, the mo- tion will he successively connnunicated to the variotis toothed wheels in the figure, and finally tu the crown-wheel or escape m e n t - wheel. I; the teeth of which so act on the two small lev- ers or pallets, 6 6, projecting from and forming jjart of the suspended upright spindle or vertical axis, IvM, on which is fixed the regulator or balance, LL, that an alternating or vibratory instead of a circular mo- tion of the balance itself is the result. The hands of the clock are attached to the wheel N, also set in motion by the cylinder B. Now, unless there were some check upon the motion, it is manifest that the heay weight A would go rapidly to the ground, causing the wheels to rotate, the balance to vibrate, and the hands to go round with increasing velocity. In order to prevent this rapid unwinding of the clockwork, and adjust it to the more deliberate measurement of time, the balance is, in De Vick's clock, loaded with two weights, m, m ; and the farther these are removed from the axis or spindle, Kil, the more heavily they will resist and coun- teract the escapement of the levers, and the rapidity of the rota- tion of the escape- ment-wheel, till the clock be brought to go neither too quick nor too slow. Upon this simple plan it is probable that all clocks were constructed until the seventeenth century, when the principle of the pendulum was ap- Fio. 3. DE ncK's OLD BAL- pHed to the science of ANCB CONVEKTED INTO THE 1,„,.„1,,,„- TllP lirnn. PENDCLDM. pp, Pallets. noiology. ine prop erty of a penduhun known as its isochronism (q.v.) constitutes its value to clock-mechanism — that. v.en a suspended body is swinging, any increase or Vol. v.— t. Fig. 2. BALANCE AXD ESCAPE. MENT OF THE FIRST CLOCK, p p, Pallets. 43 CLOCK. decrease in its speed will not change the num- ber of vibrations it makes in a given time. but only the length of the arc it describes. This law of the pendiiluiu was discovered by Galileo, and was first applied (probably) to clockwork by Huygens, aI)out Ifi.'jT. The two accomjianying cuts show how the horizontal swing of tlu> balance, as maintained in De Vick's clock, was converted into the vertical swing of the pendulum. By taking olV one of the weights and hanging the balance in an upright position, it bccouu's a |ieuduUim. Ten years later Dr. llooko invented an escapement which enabled a weaker support to carry a heavier penduhnu. Subsequent improvements in the escapement and pendulum (see Escapement: Pk.nuilum), and in the use of the spring (see Watch) in place of the pendulum, have brought the mechanism of timekeepers down to the present degree of perfec- tion. Stbiki.ng Apparatus. The principal function of a clock, according to the mediicval conception, was that it should be a reliable instrument for automatically calling out the hoirs, particularly the hours for devotion. This conception of the clock is shown in the word itself, which orig- inally meant 'bell' — a meaning which has been retained in the French word cloche. A strik- inc apparatus was. therefore, early invented, and it is interesting to note that the striking mech- anism of De Vick's clock is similar to that used in some modern timepieces. A striking clock contains one or more extra trains of wheels to control the striker. In De Vick's clock twelve pins projected from the wheel on which the hand was attached. At each hour one of these pins, by pushing a lever, released the striking-tram, which lifted the hammer that strikes the bell. The number of sti-okes was determined by the position of the notches around the edge of a locking-plate, which held the lever controlling the striking-train. These notches were so placed that at one o'clock the catch in the lever entered a notch as soon as one blow had been struck. At two o'clock there was a longer space before the notch was reached, so that the bell was struck twice -, at three o'clock the bell struck three times before the train was locked, and so on. The chief objection to this striking ap- paratus is that it is thrown out of order and strikes wrong every time the clock happens to run down. Ibe rack ana piQ_4_ dr. hooke's escapement. snail Repeating mechanhiii has been used for two centuries. It is a peculiar aiul intricate piece of mechanism. In or- dinary clocks, the impelling power is a weight sim- ilar to that which moves the lime-measuring mech- anism itself; but the pressure of this weight on the .striking machinery is only permitted to come into plav at stated periods in course of the workings' of the timekeeping apparatus— viz. at