FIG. 10.—A WATCH OF THE 16TH CENTURY.
The water-clock just described led easily and directly to the weight-clock. Clockmakers in the Middle Ages for centuries tried with more or less success to make clocks that would run by means of weights. In 1370, Henry De Vick, a German, succeeded in solving the problem. De Vick was brought to Paris to make a clock for the tower of the king's palace, and he made one that has become famous. In a somewhat improved form it can still be seen in Paris in the Palais de Justice. Let us remove the face of this celebrated timepiece and take a look at its works (Fig. 8). It had a striking part, and a timekeeping part, each distinct from the other. The figure shows only the timekeeping part. The weight (A), of 500 pounds, is wound up by a crank (the key) at P. O is the hour-hand. If A is allowed to descend, you can easily see how the whole system of wheels will be moved—and that very rapidly. But if something does not prevent, A will descend faster and faster, the hour-hand will run faster and faster and the clock will run down at once. If the clock is to run at a uniform rate and for any length of time, the power of the weight must escape gradually. In the clepsydra (Fig. 1) the descent of the weight was controlled by the size of the stream of flowing water. De Vick invented a substitute for the stream of flowing water. Fasten your attention upon the workings of the saw-toothed wheel II and the upright post K, which moves on the pivots l and k, and you may learn what he did. Fixed to the upper part of the post K is a beam or balance LL, at the ends of which are two small weights m and m, and projecting from the post in different directions are two pallets or lips i and h. Now, as the top of the wheel II turns toward you, one of its teeth catches the pallet i and turns the post K a part of the way round toward you. Just as the tooth escapes from i a tooth at the bottom of II (moving from you) catches the pallet h and checks the revolving post and turns it from you. Thus as II turns, it gives a to-and-fro motion to the post K and, consequently, a to-and-fro motion to the balance LL. II is called the escapement because the power of the descending weight gradually escapes from its teeth. In the clepsydra the trickling of water regulated the descent of the weight; in De Vick's clock the trickling of power or force from the escapement regulated the descent of the weight. The invention of this escapement is the greatest event in the history of the clock. The king was much pleased with De Vick's invention. He gave the clockmaker three shillings a day, and allowed him to sleep in the clock tower; a scanty reward indeed for one who had done so much for the world, for De Vick's invention led rapidly to the excellent timepieces of to-day, to both our watches and our clocks. After the appearance of the weight-clock, the water-clock gradually fell into disuse, and all the ingenuity of the clockmaker was bestowed upon weights and wheels and escapements and balances. A century of experimenting resulted in a clock without a weight (Fig. 9). In this timekeeper you recognize the beginnings of the modern watch. The uncoiling of a spring drove the machinery. Instead of the balancing beam with its weights as in De Vick's clock, a balance wheel is used. The escapement is the same as in the first weight-clock. The busy and delicately-hung little balance wheel in your watch is a growth from De Vick's clumsy balance beam. The spring-clock would run in any position. Because it could be carried about it led almost at once to the watch. Many places claim the distinction of having made the first watch, but it seems that the honor belongs to the city of Nürenburg. "Nürenburg eggs," as the first portable clocks were called, were made as early as 1470. The first watches were large, uncouth affairs, resembling small table clocks but by the end of the sixteenth century small watches with works of brass and cases of gold or silver were manufactured (Fig. 10).
FIG. 11.—GALILEO'S PENDULUM. (1650.)
FIG. 12.—THE FIRST PENDULUM CLOCK. (1656.)
The last important step in the development of the clock was taken when the pendulum was brought into use. The history of the pendulum will always include a story told by Galileo. This great astronomer, the story runs, while worshiping in the cathedral at Pisa one day, found the service dull, and began to observe the swinging of the lamps which were suspended from the ceiling. Using his pulse as a timekeeper he learned that where the chains were of the same length the lamp swayed to and fro in equal length of time, whether they traveled through a short space or a long space. This observation set the philosopher to experimenting with pendulums of different lengths. Among the many things he learned one of the most important was this: a pendulum thirty-nine inches in length will make one vibration in just one second of time. Now, if the pendulum could only be kept swinging and its vibrations counted it would serve as a clock. Galileo, of course, saw this, and he caused to be made a machine for keeping the pendulum in motion (Fig. 11), but he did not make a clock; he did not connect his pendulum with the works of a clock. This, however, was done about the middle of the seventeenth century, although it is somewhat difficult to tell who was the first to do it. The honor is claimed by an Englishman, a Frenchman, and a Dutchman. The truth is, clockmakers throughout Europe were trying at the same time to make the best of the discoveries of Galileo, and several of them about the same time constructed clocks with pendulums. The one who seems to have succeeded first was Christian Huygens, a Dutch astronomer, who, in 1656, constructed a clock, the motions of which were regulated by the swinging of a pendulum (Fig. 12). The weight was attached to a cord passing over a pulley and gave motion to all the wheels, as in De Vick's clock. Like De Vick's clock also Huygens's clock had its escapement wheel acting upon two pallets. In the Dutchman's clock, however, the escapement, instead of turning a balance beam to and fro, acted upon the pendulum, giving it enough motion to keep it from stopping.
We need not carry our story further than the invention of Huygens. Timepieces are cheaper and better made and more accurate than they were two hundred years ago, but no really important discovery has been made since the pendulum was introduced.