accurate “time measure” yet made. [Illustration: VIEW OF ESCAPEMENT MAKING DEPARTMENT] Watches are made to measure time. If anything is to be measured there must be some standard with which to compare it, for we have seen that measuring is a process of comparing a thing with an appropriate or acknowledged and fixed standard. The only known standard for the measurement of time is the movement of the earth in relation to the stars. It has taken thousands of years for mankind to learn what is now known concerning time. It has also taken hundreds of years to secure the wonderful accuracy in the measuring of time which has now been attained. We have said that nothing has been devised which will equal the accuracy of a “pendulum clock.” A story was told of a professor of a theological seminary who was one day on his way to a jeweler’s store, carrying in his arms the family clock, which was in need of repairs. He was accosted by one of his students with the question, “Look here, Professor, don’t you think it would be much more convenient to carry a watch?” A pendulum clock must of necessity be stationary, but it is now needful that people should be able to have a timepiece whenever and wherever wanted. This need is supplied by the pocket watch. [Illustration: TIME TRAIN OF A WATCH] If Galileo watched the swinging of the big chandelier long enough he found that the distance through which it swung was gradually diminishing, till, at last, it ceased to move; what stopped it? It was one of the great forces of nature, which we call gravitation, and the force which kept it in motion we call momentum. But gravitation overcame momentum. In order to maintain the constant vibration of a pendulum it is needful to impart to it a slight force, in a manner similar to that given by a boy who gives another boy a slight “push,” to maintain his movement in a swing. A suspended pendulum being impossible of application to a pocket watch, a splendid substitute has been devised--in the form of the balance wheel of the watch, commonly called the “balance.” The balance is, in its action and adaption, the equivalent of the vibrating, or oscillating, pendulum; and the balance spring (commonly called the hairspring), which accompanies it, is in its action equivalent to the force of gravity in its effect upon a pendulum. For the tendency and (if not neutralized by some other force) the effects of the hairspring upon the watch balance, and of gravitation on the pendulum, are to hold each at a position of rest, and consequent inaction. [Illustration] [Illustration] But we have in a pocket watch a “mainspring” to actuate the train of gear wheels which by their ultimate action give the delicate “push” to the balance wheel at distinct intervals, and so keep the balance in continued motion. In the same manner, the “weight” of a clock, acting through the force of gravity, carries the various wheels of the clock train, and gives the slight impulse to the swinging clock pendulum.