CHAPTER XV

CLOCKS

The matters of every-day life, much less the affairs of a complex civilization, could scarcely be carried on without some accurate and uniform system of measuring time. Nature herself furnishes measurements for certain divisions of time. The "two great lights" that God made, as the Bible tells us, were designed "for signs, and for seasons, and for days and for years." The revolution of the earth around the sun marks the year; the revolution of the moon around the earth determines the month; the rotation of the earth on its axis causes and measures day and night. But no object of nature distinguishes the hours of the day or the divisions of the hour.

Man requires a smaller unit of time than the day. He must divide the day into hours; the hours into minutes; the minutes into seconds. The division of the day into twenty-four hours is as old as authentic history. But the means for determining the hours and their subdivisions were at first quite crude and inefficient.

Perhaps the most primitive of all time-measuring devices was a stick or pole planted upright in a sunny place. The position of the shadow which it cast marked time. The sun-dial was a development of this simple device. It consisted essentially of two parts: a flat plate of metal marked off much like the dial of a modern clock or watch, and an upright piece, usually also of metal, fastened to the center of the dial. To make the direction of the shadow uniform for any given hour throughout the year, the upright piece was made parallel to the axis of the earth. As the earth rotated on its axis the shadow cast by the upright piece moved from point to point on the dial, measuring the flight of time. The sun-dial was in use among the earliest nations. Herodotus is authority for the statement that the Greeks borrowed it from the Babylonians. The sun-dial was obviously of no use on cloudy days or dark nights, and even in sunny weather it could not accurately or delicately indicate the passage of time. However, it continued in use so long that to the end of the seventeenth century the art of dialling was considered a necessary element of every course in mathematics.

Another ancient invention for measuring time was the water-clock. Water was permitted to drop from a small orifice in a containing vessel. The period required for emptying the vessel marked a unit of time. Its principle was the same as the common hour-glass, according to which time is measured by the slow dropping of sand from one receptacle into another. The water-clock was used by the ancient Chaldeans and the Hindoos, and also by the Greeks and Romans. Demosthenes mentions its use in the courts of justice at Athens.

In order to mark the hours of the day, the Saxon King Alfred the Great is said to have made wax candles twelve inches in length, each marked at equal distances. The burning of six of these candles in succession consumed, roughly, just twenty-four hours. To prevent the wind from extinguishing them they were inclosed in cases of thin, white, transparent horn. The candles thus inclosed were the ancestors of the modern lantern.

Our word _clock_ comes from the Anglo-Saxon verb _clocean_ meaning "to strike," "to give out a sound." It is impossible to ascertain by whom clocks were invented, or when or where. It is fairly clear, however, that a Benedictine Monk named Gerbert, who afterward became Pope Sylvester II, made a clock for the German city of Magdeburg a little before the year 1000 A.D. Clocks may have been made before this, but if so it would be hard to establish the fact. In Gerbert's clock weights were the motive power for the mechanism. Weight clocks were used in the monasteries of Europe in the eleventh century, but it is probable that these early clocks struck a bell at certain intervals as a call to prayer, and did not have dials for showing the time of day.

The first clocks were comparatively by large and were stationary. Portable ones appeared about the beginning of the fourteenth century, though the inventor is not known, nor the exact time or place of invention. When portable clocks were invented, the motive power must have been changed from weights to main-springs, and this change in motive force marks an era in the development of the clock. The introduction of the pendulum as a regulating agent was, however, the greatest event in clock development. This invention has been credited to Huygens, a Dutch philosopher, who was certainly, if not the discoverer of the pendulum, the first to bring it into practical use, about 1657. Credit for inventing the pendulum is also claimed for Harris, a London clockmaker; for Hooke, the great English philosopher; for a son of Galileo, the celebrated Italian scientist; and for others.

The modern watch is in reality but a developed type of the clock. Watches were made possible by the introduction of the coiled spring as motive power, instead of the weight. The coiled spring came into use near the end of the fifteenth century, though it is not known where or by whom it was invented. Watches were not introduced into general use in England until the reign of Elizabeth, and then on account of the cost they were confined to the wealthy. At first watches were comparatively large and struck the hours like clocks. After the striking mechanism was abandoned, they were reduced in size and for a time were considered ornamental rather than useful. They were richly adorned with pictures in enamel and with costly jewels. They were set in the heads of canes, in bracelets, and in finger-rings.

Watches and clocks had originally only one hand, which indicated the hour. Minute and second hands were added later. Devices have been introduced to counteract the effect of temperature on the mechanism of time-pieces, so that they run uniformly in all kinds of weather. Within recent years clocks operated with electricity have been invented. With the advent of clock and watch manufacture by machinery, the cost has been so reduced that practically any one may own an accurate time-piece. The United States is one of the foremost countries of the world in the manufacture and sale of clocks and watches.