Makers of Many Things

by Eva March Tappan

VIII
HOW THE WHEELS OF A WATCH GO AROUND

If an electric automobile could be charged in fifteen seconds and then would run for forty hours without recharging, it would be looked upon as a great wonder; but to wind a watch in fifteen seconds and have it run for forty hours is so common that we forget what a wonder it is. When you wind your watch, you put some of the strength of your own right hand into it, and that is what makes it go. Every turn of the key or the stem winds up tighter and tighter a spring from one to two feet long, but so slender that it would take thousands to weigh a pound. This is the main spring. It is coiled up in a cup-shaped piece of metal called a "barrel"; and so your own energy is literally barreled up in your watch. The outer end of this spring is held fast by a hook on the inside of the barrel; the inner end is hooked to the hub of a wheel which is called the "main wheel," and around this hub the spring is coiled.

This spring has three things to do. It must send the "short hand," or hour hand, around the dial or face of the watch, once in twelve hours; it must send the "long hand," or minute hand, around once an hour; and it must also send the little "second hand" around its own tiny circle once a minute. To

do this work requires four wheels. The first or main wheel is connected with the winding arrangements, and sets in motion the second, or center wheel, so called because it is usually in the center of the watch. This center wheel revolves once an hour and turns the minute hand. By a skillful arrangement of cogs it also moves the hour hand around the dial once in twelve hours. The center wheel moves the third wheel. The chief business of the third wheel is to make the fourth turn in the same direction as the center wheel. The fourth wheel revolves once a minute, and with it turns the tiny second hand.

Suppose that a watch has been made with only the main spring, the four wheels, and the three hands, what would happen when it was wound? You can tell very easily by winding up a mechanical mouse or a train of cars or any other toy that goes by a spring. It will go fast at first, then more and more slowly, then it will stop. This sort of motion might do for a mouse, but it would not answer for a watch. A watch must move with steadiness and regularity. To bring this about, there is a fifth wheel. Its fifteen teeth are shaped like hooks, and it has seven accompaniments, the balance wheel, the hair spring, and five others. This wheel, together with its accompaniments, is able to stop the motion of the watch five times a second and start it again so quickly that we do not realize its having been stopped at all. A tiny arm holds the wheel firmly, and then lets it escape. Therefore, the fifth wheel and its accompaniments are

called the "escapement." This catching and letting go is what makes the ticking.

A watch made in this way would run very well until a hot day or a cold day came; then there would be trouble. Heat makes metals expand and makes springs less elastic. Therefore in a hot day the watch would go more slowly and so lose time; while in a cold day it would go too fast and would gain time. This fault is corrected by the balance, a wheel whose rim is not one circle, but two half-circles, and so cunningly made that the hotter this rim grows, the smaller its diameter becomes. In the rim of the wheel are tiny holes into which screws may be screwed. By adding screws or taking some away, or changing the position of some of them, the movement of the watch can be made to go faster or slower.

All this would be difficult enough to manage if a watch was as large as a cart wheel, with wheels a foot in diameter; but it does seem a marvel how so many kinds of wheels and screws and springs, one hundred and fifty in all, can be put into a case sometimes not more than an inch in diameter, and can find room to work; and it is quite as much of a marvel how they can be manufactured and handled.

Remembering how accurate every piece must be, it is no wonder that in Switzerland, where all this work used to be done by hand, a boy had to go to a "watch school" for fourteen years before he was considered able to make a really fine watch. He began at the beginning and was taught to make, first, wooden handles for his tools, then the tools themselves,