Page:The New International Encyclopædia 1st ed. v. 20.djvu/399

* WATCH. 331 WATCH. carding of fusee; (8) introihiction of automatic uiaoliinery for the construction of tlie parts. The mechanism or "movement' of a modern American watch consists of a scries of wheels called the truin, the first of which, named the bar- Fig. 1. BAL^tNCE WHEEL. re/, contains the main-spring, in which the power .secured when the watch is wound up is stored. The train transmits to the desired points the motion stored up in the spring. At the end of the train is the escapement — a delicate and com- Fic. 2. plex mechanism which so regulates the motive force stored up in the main-spring that it is expanded with uniformity and at the desired rate. The train of wheels is placed in a circular position as shown in Fig. 2 so as to accommodate the shape of the watch, but the order is best understood by arranging them in a straight line, as in Fig. 3. It has been seen that the first wheel of the train, the barrel, contains the main-spring and is therefore connected with the stem-winding attachment. A little click or pawl, working in the teeth of a ratchet fastened to the main-spring Vol. XX.— 22. arbor, keeps the latter from running backward. The second wheel of the train, called the centre tvheel, is always placed in the centre of the watch, because connected with it on the same staff are the wheels which drive the minute and hour hands. The centre wheel meshes into the third pinion, upon which tiie third wheel is firmly fixed. This turns the fourth pinion, which carries a wheel gearing into the escape pinion, upon which the escape vhcci is carried. The second or centre pinion is attached to a centre staff, which projects through the main plate of the watch. Upon this projecting porlitm is mounted another pinion, which from its shajie is called the cannon pinion. The minute hand is fitted upon the hub of this pinion an<l its teeth drive a little wheel which is commonly known as the minute wheel. Attached to this wheel is still another pinion geared to drive the hour wheel, which is mounted on the long hub of the cannon pinion. Upon the hub of the hour wheel the hour hand is placed. The ninuber of teeth on each of these w-heels and pinions (which are generally called the dial vheels) is so arranged that wliile the cannon pinion, carrying the minute hand, makes a com- plete revolution in one hour, the hour wheel, carrying the hour hand^ revolves once in twelve hours. The stem attachment for setting the watch is connected with one or other of these dial wheels. Keturning now to the wheel train, we find that the fourth pinion has a pivot which projects through the frame plate and upon this pivot the second hand is mounted. Hence it is necessary that the fourth pinion and wheel should make a revolution once a minute, or 60 times as fast as the centre staff. This is accomplished by means of the proportioning of the centre wheel, third pinion and wheel, and fourth pinion to each other. Con- sidering, no«', the last wheel of the train and its va- rious attachments, which are grouped together under the general name of escapement. we find that the group con- sists of seven members : The escape uheel. the pallet, the fork, the roller and roller pin, the halanee-whecl. and the hnir-sprin(j. The use of each part is explained far- ther on. The combined object of the whole group is to stop and then set in motion again, at regular intervals, every wheel in the train — an action which causes the familiar tick of the watch. The teeth of the escape- wheel, instead of being cut on the epicycloidal curve like the other teeth of the train, so as to convey mo- tion with as little loss of power as possible, are constructed with an entirely different object and in an entirely different form. Thej' form a series of fifteen hooks. An anchor-shaped piece, called the pallet, is so hung that first one and then the other of its horns is locked into the tooth of the escape wheel as it revolves. These locking horns are usvially made of some precious stone. The unlocking is accomplished by a lever Fig. 4.