Having traced out the history of the clock and watch mechanism all the way from De Vick's first clock and the clumsy old Nuremberg Egg down to the perfect time-keeping device which we have today, it may be interesting to look a little more closely at the result of so many years and so many inventions—to see what its parts are, and how they are put together, and to observe how the wonderful little machine does its work.

Modern clocks and watches are nearly enough alike in their structure and way of working, so that if we understand the one, we shall easily understand the other also. The differences between them are few and slight and easy to explain. So let us take for our example a typical modern watch movement, which is easily the more beautiful and interesting mechanism of the two.

First of all, as we saw in the days of De Vick and Henlein, a watch, or a clock, is a machine for keeping time. So it must have three essential parts: first, the power to make it go; second, the regulator to make it keep time; and third, the hands and face to show plainly the time it keeps. Each of these three parts is itself made up of several others.

The power or energy which runs the watch is put in to it by the winding which coils up the mainspring. The outer end of this spring is attached to the rim of the main wheel (1) and after the spring is wound this wheel would whirl round and let the spring run down instantly if there was nothing to stop it. The teeth on this wheel, however, are geared into the second or center pinion (as shown in illustration at "A") which makes it run the entire movement while running down slowly instead of flying round and uncoiling at once.

As we will see later, the spring-power is transmitted through the train of wheels and the lever (7) to the balance wheel (8) which lets the escape wheel (5) turn a little each time it swings, while it simultaneously receives, by means of the lever from the escape wheel, the "impulse" or power which keeps it running. Thus the swinging of the balance lets the mainspring down gradually while drawing its power from it. The spring is made as thin as it can be and still have power enough to make the watch go. For a modern watch, this is about one flea-power. One horse power, which is only a small fraction of the power of the average automobile, would be enough to drive all the millions of watches in the world.

The center pinion into which the mainspring is geared is attached to its staff to which is also fastened the large center-wheel (2) so that the spring cannot turn this pinion without also turning the center wheel. But the center wheel is, itself, geared into the third pinion, which is attached to the third wheel (3), and this again is geared into the fourth pinion attached to the fourth wheel (4). The fourth wheel gears into the escape pinion which revolves with the escape wheel (5), so that none of these wheels or pinions can turn except when the escape wheel does. But there is a constant pressure from the spring on all of these wheels, which together constitute what is called the train.

The escape wheel, therefore, wants to turn continually and if it was not restrained it would revolve rapidly, letting the movement run down. But it is retarded and can only turn from one tooth to the next, each time the balance (8) turns. This action is secured by connecting the balance and the escape-wheel by means of the lever (7), one end of which forms an anchor shaped like a rocking-beam, called the pallet (6). In the pallet are two jewelled projections called the pallet-jewels which intercept the escape-wheel by being thrust between its teeth, letting it turn a distance of only one tooth at each swing of the balance as the pallet rocks back and forth.

The other end of the lever is fork-shaped, having two prongs. On the staff with the balance instead of a pinion as all the other wheels have, is a plain, toothless disc called the roller, from the lower side of which projects a pin or rod made of garnet. This is called the jewel-pin or the roller-jewel. The roller being fastened to the balance-staff, of course, turns just as the balance turns and with it the jewel-pin. And the lever is just long enough and is so placed that every time the balance turns, the jewel-pin fits into the slot between the prongs of the lever-fork carrying it first one way, and then, as the balance comes back, the other way. Thus the lever is kept oscillating back and forth, rocking the pallet and withdrawing one pallet-jewel, releasing the escape-wheel just long enough to let it run to its next tooth before the other pallet-jewel is thrust in to stop it. It is a beautiful thing, to watch, like the beating of a tiny heart, or the breathing of a small quick creature. The hairspring (9) almost seems to be alive. And indeed, it is in a way, the very pulse of the machine.

There is only one more important point to understand. You know how the power gets as far as the escape wheel from the mainspring, and how the motion of the balance lets the escape-wheel revolve a tooth at a time, but you have still to learn how the power which keeps the balance rotating reaches it from the escape-wheel through the lever. Here is the most interesting feature of a watch movement.

After the balance has been started, its momentum at each turn starts the lever when the jewel-pin strikes it, but unless the balance was constantly supplied with new power it would soon stop, and the watch would not run. It will be noticed, however, from the illustration, that the teeth of the escape-wheel are peculiar in shape and very different from those of the other wheels. The ends of the pallet-jewels are also cut at a peculiar angle.

Now, each time just before the jewel-pin starts to shift the lever from one side to the other, the latter is in such a position that one of the pallet-jewels is thrust in so that its side is against that of one of the teeth of the escape-wheel, keeping it from turning. But the instant the lever commences to move it begins to draw this pallet-jewel outward from the tooth until the corner of the jewel passes the corner of the tooth. Then the escape-wheel is released and the power that is behind it makes it turn quickly, and on account of the shape of the tooth, it gives the pallet-jewel a sharp push outward, swinging the lever, causing it at the other end to impart a quick thrust to the jewel-pin, thereby accelerating the speed of the balance and renewing its momentum.

Thus the balance receives the power to keep it in motion, swinging it as far as the hairspring allows. The hairspring then reverses it and swings it until the jewel-pin again starts the lever in the other direction, releasing the escape-wheel from which it receives another "impulse" and so on as long as the mainspring is kept wound. A watch in perfect time ticks five times to the second. That means 18,000 swings of the balance every hour, or 432,000 in a day. And in that time, the rim of the balance travels about ten miles.

A clock is essentially only a larger and stronger watch, just as a watch is a clock made small enough and light enough to be carried about conveniently. But the working of the two is practically the same. They are but different members of the same family, varying types of one time-keeping machine which is among the most ingenious and valuable things that man has made.

One interesting thing to know about a watch is that if it is keeping good time, it will serve for a fairly accurate compass. So if you are ever lost in the woods, your watch may help you out again. Lay it flat face upward, and point the hour hand toward the sun. Then South will be in the direction half way between the hour hand and the figure 12, counting forward as the hands turn in the morning hours, and backward in the afternoon. This is because the hour hand moves around the dial just twice as fast as the sun moves around the sky, making a full circle in twelve hours while the sun makes its half circle from horizon to horizon.

Now, the sun is always to the southward of you as you are anywhere north of the equator. At noon, the sun is practically due South. At that hour, both hands of your watch are together on the figure 12 and the hour hand pointing at the sun points in that direction. At 6 a.m. the sun is nearly East, so if the hour hand, now on the figure 6 is pointed eastward toward the sun, then South would be in a line just over the figure 9. At 6 p.m., the sun being in the west and the hour hand pointed at it, South would be half-way back toward the figure 12, or just over the figure 3. For other morning or afternoon hours, the same reasoning holds true.