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. [Illustration: _A Modern Watch Movement_] 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.