It's great fun to hold a watch up to a baby's pink ear. He is so as-ton-ished by the busy tick-tick-ticking. One little girl remembers thinking a Brownie did the ticking, and that the mouse that ran up the clock did the striking. When the little gold back doors were snapped open, she fully expected to see a live playmate pop out. Before any child can talk plain he wants to know what makes the wheels go 'round.

Once there were only clocks, and clocks without ticks, at that. A clock without a tick seems as odd as the smile without a cat in Alice in Wonderland. In pictures, Old Father Time carries an hourglass clock. In an hour-glass it takes just one hour for the sand to run through a little hole from one hollow glass cone to another. It is wound up by turning it over at the end of every hour. Really, Father Time ought to carry the sun, or a bunch of fire-cracker stars. They are the oldest and best timekeepers.

If you were to stand still, all day, in a sunny field, and watch your shadow grow shorter, up to noon, then jump around to the other side and grow longer until sunset, you might think of making a shadow clock, or sun-dial. A sunbeam, shining through a hole in a roof, makes a moving golden spot on the floor below. If you ever go across the ocean to the old world, you may see stone sun-dials in castle gardens, and clock-faces in the marble floors of great churches. Shadows and sunbeams were the first hour hands.

In old, old times people didn't have to catch trains, nor little children go to school, so minutes were not very important. But they did want to measure the exact length of eclipses of the sun and moon. A little over three hundred years ago, a great astronomer named Galileo was in a church, when some one bumped into a hanging bronze lamp and set it swinging. Back and forth it went, back and forth, as regularly as—guess! The pendulum of a grandfather's clock. When it slowed down and stopped—when "the old cat died," as you say when you stop swinging, he started it again with a push.

You can make a pendulum with an apple and a string hung from a gas jet. It took another hundred years to fit wheels and weights to pendulums so they could be kept swinging for a whole day and night.

To understand what makes the wheels go 'round in papa's watch, a little boy or girl would better begin with the big grandfather's clock in the hall. What a broad, pleasant, honest face it has. Twelve numbers it has, evenly spaced on a circle, like the old stone sundials, and two hands moving around to point the hours and minutes. On the lower side is a small dial with a tiny hand racing around it and counting the seconds. The hour and minute hand are fastened to axles that are pushed through a hole in the middle of the dial. Axles are the centers of wheels, you know, so there are wheels behind the dial. In the face of the clock are two more holes. These are key holes for winding up the weight and the hammer that strikes the hours. A watch has no key holes. It is wound up by the stem.

That is all you can see until you open the tall, narrow door below the face. There, in a sort of closet, the long pendulum swings back and forth, its bright brass "bob" winking in the light. And, at one side, a heavy iron weight hangs on a stout cord. "Tick-tock" is all a clock says to most grown-up people. But to children and poets it says all sorts of things. One thing it says, if you are small enough to squeeze in behind the pendulum, is: "Tick-tock,

fennel-and-dock, jump-in-quick and climb-up-the-clock!" If you were a Brownie you could scramble right up the pendulum rod or the weight cord and find the "tick."

But eyes can climb where little boys can't. Look up into that Chinese puzzle of wheels behind the clock dial. The pendulum rod goes up to a sort of beam near the roof. There it is hung by a thin slip of steel that bends easily and makes a spring. It allows the pendulum to swing just so far, and then gives it a little push back. Now look up the weight cord. The cord is ever so long. The upper end of it is wound around a drum or barrel, very much as the rope of an old oaken bucket is wound on a windlass. The weight pulls on the cord and barrel all the time, but it cannot move them until the pendulum is set swinging. Start the pendulum and see what happens. The whole clock wakes up, like the palace in Sleeping Beauty.

The pendulum lifts one leg of an anchor-shaped piece of metal that is locked in the saw-teeth of a wheel. When this wheel is unlocked it turns a little. This allows the barrel to turn. The cord and weight pull on the barrel, too, to help it turn. And this sets all the other wheels in motion. You didn't know that all the wheels in a clock are called a "train of wheels" did you? They are all coupled together, just as a train of cars are, and travel together. The pendulum seems to be the engineer; the locked wheel is the throttle; the barrel, cord and weight are the engine, furnishing the power to pull the train. The locked wheel is a safety valve, too, as well as a throttle.

The little saw-toothed wheel and the anchor, or lever catch, are there to tell all the other wheels not to go too fast. Every time the pendulum swings, a tooth of this wheel is let go. Then another tooth is caught and held an instant. This catching and letting go make the clicking or ticking sound in watches, and the solemn tick-tock of big clocks. The wheel and the catch are called the "escapement," because the wheel turns around, or escapes, only one tooth at a time. At every tick the escapement says: "Not-so-fast," and at every took, "Go-ahead." You see, when the cord and weight begin to pull on the barrel, it would whirl over and over, as fast as it could, if nothing held it back. Then all the wheels would fairly race, until the weight had dropped to the bottom. There would be a grand smash-up, if the escapement wasn't there to hold them all to a steady gait.