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.