In all this journey, covering thousands of years, one thing has made itself clear to us—the story of timepieces is not a mere mechanical story; it is a human story. Men did not put together certain pieces of wood or metal in order merely to make mechanism, but to meet a vital need. One might almost say that the story of the watch is in the watch itself. The works run and the hands move because of the mainspring, which by pressing steadily forces them into motion. In very much the same way, the busy brains of the inventors and the busy hands of the workmen have been kept active because advancing civilization has been like a great mainspring, always pressing upon larger affairs and greater numbers of people, always needing to fit its engagements more and more closely together, and always calling for better and better means for telling time. Thus, if the watch in the days of Shakespeare and Queen Elizabeth was still an inaccurate timepiece, its improvement was a foregone conclusion. Brains and hands were still active; civilization was still pressing. It is said that a hog helped in the next development; he helped quite unconsciously by furnishing a bristle. In order to understand this, we must remember Galileo's swinging lamp and the pendulum that the Englishman, Hooke, and the Hollander, Huyghens, applied in the making of clocks. It will be recalled that a pendulum swings in arcs of different lengths in exactly the same time and that this property is called _isochronism_. Both Hooke and Huyghens could see that the application of isochronism would be quite as valuable in a watch as in a clock, but they realized that this could not be accomplished by means of the pendulum. Therefore, each began to experiment, and each seems to have hit upon the same idea as a substitute for the pendulum in about the year 1665. This is where the hog's bristle came into use. One end was made fast while the other was bent back and forth by the balance, as it swung to and fro. Being short and stiff, it acted as a spring; in fact, its motion was something like the swing of a small pendulum, and some people incorrectly claim that the name of _hair-spring_ first came from this use of a hair. Of course, a very fine steel was soon substituted for the bristle. Next, it was realized that there would be an advantage if a much longer spring were used, and obviously the only way in which this could be done was by making it in the form of a coil, and so we have the delicate, coiled hair-spring, as it is found in our own watches to-day. The principle of the hair-spring is not unlike that of the pendulum: the farther the pendulum is swung out from the lowest point of its arc, the greater is the force that gets it back; and the farther a spring is bent from its position of rest, the greater is the force exerted to get it back. With both of these devices it is possible to obtain regular beats and steady motion.