Читать книгу Time Telling through the Ages - Harry Chase Brearley - Страница 12

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We learn that toward the close of the thirteenth century a clock was set up in St. Paul's Cathedral in London (1286); one in Westminster, by 1288; and one in Canterbury Cathedral, by 1292. The Westminster clock and the chime of bells were put up from funds raised by a fine imposed on a chief justice who had offended the government. The clock bore as an inscription the words of Virgil: "Discite justitiam moniti," "Learn justice from my advice," and the bells were gambled away by Henry VIII! In the same century, Dante, whose wonderful poem the Commedia, (the Inferno, Purgatory and Paradise) is sometimes called the "Swan Song of the Middle Ages," since it marks the passing of the medieval times, spoke of "wheels that wound their circle in an orloge."

Chaucer speaks of a cock crowing as regularly "as a clock in an abbey orloge." And this shows, curiously, the early meaning of the word, for by the word "clock," Chaucer evidently meant the bell which struck the hour, and, very obviously, he used the word "orloge" to indicate the clock itself.

Many of these "clocks" had neither dials nor hands. They told time only by striking the hour. Sometimes in the great tower clocks there were placed automatic figures representing men in armor or even mere grotesque figures which, at the right moment, beat upon the bell. These figures were called "jacks o' the clock" or "jacquemarts" and curious specimens of them are still in existence.

The early abbey clocks did not even strike the hour but rang an alarm to awaken the monks for prayers. Here again, the alarm principle precedes the visible measurement of time; even now, as already noted, we speak of a "clock" by the old word for "bell."

In the course of the following century—the fourteenth—clocks began to appear which were really worthy of the name, and of these we have authentic details. They were to be found in many lands. One of them was built, in 1344, by Giacomo Dondi at Padua, Italy. Another was constructed in England, in 1340, by Peter Lightfoot, a monk of Glastonbury. And in 1364, Henry de Wieck, De Wyck, or de Vick, of Wurtemburg, was sent for by Charles V, King of France, to come to Paris and build a clock for the tower of the royal palace, which is now the Palais de Justice. It was finished and set up in February 1379, and there it still remains after lapse of five and a half centuries, although its present architectural surroundings were not finished until a much later date.

This venerable timepiece termed by some chroniclers "the parent of modern timekeepers," was still performing its duty as late as 1850. And so it is a matter of interesting record that its mechanism, which served to measure the passage of time in the days when the earth was generally believed to be flat and when the Eastern Division of the Roman Empire was still ruled from Byzantium, now Constantinople, has served the same purpose within the possible memory of men now living. Its bell has one grim association—it gave the signal for that frightful piece of Medicean treachery, the Massacre of St. Bartholomew, planned by Catherine de Medici, the mother of the King Charles IX, when the armed retainers of the crown of France flung themselves upon the unsuspecting Huguenots and caused the streets to run red with the blood of men, women and children—a ghastly butchery of thousands of people.

As we have seen, de Vick's clock was neither the earliest made, nor among the earliest; nor, probably, did it embody any at that time new mechanical invention. It does, however, fairly and clearly typify the oldest style of clock of which we to-day have any accurate knowledge. Compare its description, then, with the clock upon your shelf.

We think of the tall-cased "grandfather's clocks" as antique; but this tower-clock of de Vick's outdoes them in antiquity by some four hundred years. And its most interesting feature is its curious likeness in mechanical principle to the clocks of modern times. Like most early clocks, it has only one hand—the hour-hand. Its ponderous movement is of iron, laboriously hand-wrought; the teeth of its wheels and pinions were cut out one by one. It was driven by a weight of five hundred pounds, the cord of which was wound round a drum, or barrel. This barrel carried, at one end, a pinion, meshing with the hour-wheel, which drove the hands; the flange at the other end of the barrel formed the great wheel, or first wheel of the train. This meshed with a pinion on the shaft of the second wheel, and this in turn with a lantern-pinion upon the shaft of the escape-wheel. All of this is, of course, essentially the modern train of gears, only with fewer wheels.

The escapement is the most important part of the whole mechanism, because it is the part which makes the clock keep time. It is an interrupter, checking the movement almost as soon as, under the urge of the mainspring, it starts forward. The frequency and duration of these interruptions determines the rate of running. Without this, the movement would run down swiftly; with it, the operation stretches over thirty hours, involving 432,000 interruptions.

A Time Piece of the Middle Ages

The huge and elaborate Clock of Strasbourg Cathedral, in Lorraine, was built in 1352 and is an example of the first clocks.

De Vick's escapement is shown in the illustration. The escape-wheel was bent into the shape of a shallow pan, so that its toothed edge was at a right angle to the flat part of the wheel. Near it was placed a verge, or rotating shaft, so called from a Latin word meaning "turning around." On this verge were fastened two flat projections called pallets, diverging from each other at about an angle of one hundred degrees. The width between the pallets, from center to center of each, was equal to the diameter of the wheel, so that one would mesh with the teeth at the top of the escape-wheel and the other with the teeth at the bottom.

de Vick's Clock

Now, if the upper pallet were between the teeth at the top of the wheel, the pressure of the wheel trying to turn would push it away until the teeth were set free. But, in so doing, it would cause the verge to turn and bring the lower pallet between the teeth at the bottom of the wheel. And since the bottom of the wheel was, of course, traveling in the opposite direction from the top, the action would be reversed, and the lower pallet would be pushed away, bringing the upper one back between the teeth of the wheel again; and so on, "tick-tock," the wheel moving a little way each time, and the pallets alternately catching and holding it from going too far.

The device was kept running slowly by means of a cross-bar called a "foliot," fastened across the top of the verge in the shape of a T, and having weights on its two ends. When this weighted bar was set turning in one direction, it would, of course, resist being suddenly stopped and started turning the other way, as it was constantly made to do. And this furnished the regulating action which retarded the motion of the works and kept them from running down.

This involves the principle of the modern balance-wheel in both watches and clocks, which is that of inertia; the rim of the balance-wheel represents the weights on the bar that resist the pull of the pallets. A vital improvement, however, is the interception of the hair spring which gives elasticity to the pull and thus supplies the elements of precision and refinement. The inertia of the balance-wheel is gauged by the weight of the rim and its distance from the center; and the last refinement of regulation of the mechanism is produced by moving the tiny screws on the periphery of this wheel outward or inward.

We shall see later how this old escapement was in principle much like the improved forms in use to-day. It was as quaint and clumsy an affair as the first automobile or the first steam-engine. But, like them, it was a great invention, destined to achieve great results. For it was the means of making a machine keep time. And every clock and watch in use to-day depends for its usefulness upon a similar device. The tick is the first thing we think of in connection with a clock; and it is the most essential thing also, because it is the escapement which does the ticking.

This old clock of de Vick's also struck the hours upon a bell and in very much the same way as modern clocks are made to do. But the mechanical means by which it did so are too complicated to be easily described here. And indeed it is unnecessary to do so, since the bell is far less important. A clock need not strike, but it must keep time.

On the fearsome eve of St. Bartholomew, therefore, and again within the past generation, the clanging of this old clock's bell was brought about by the whirling gears and ponderous weights of an early craftsman who wrought his work into the ages.

As already stated, de Vick's mechanism embodied mechanical principles which, although greatly developed and improved, are employed even at the present day. All the essentials of a clock are there; the motive power—the descent of a massive weight—is now replaced by a slender spring; the train of gears by which this motion is reduced and communicated, are cut to-day with the extreme accuracy of modern machine work; the hand moving around the dial is now accompanied by a longer, swifter hand to tell the minutes; the escapement which by checking the motive power while yet allowing it to move on step by step, retards and regulates—even the numbered striking of the unchanging hours.

De Vick's old clock may have been a crude machine—it certainly was a poor timekeeper—but it was the sturdy ancestor of all those myriad tribes of clocks and watches which warn us solemnly from our towers, chime to us from our mantels, or, nestling snugly in our pockets, or clinging to our wrists, help us to maintain our efficiency in the complexities of modern life. The mechanism employed by de Vick was retained without any improvement of importance in all the time-pieces of the next three hundred years. The foliot escapement, especially, remained in use much longer. Indeed, any modern watchmaker would recognize that it was practically a horizontal balance-wheel.

Long before it was improved upon, watches had been invented and clocks had everywhere become common. But we shall reserve the watch for the next chapter; for the moment, our concern is with clocks alone.

The disadvantage of the medieval clock was its inaccuracy. This was due first to crude workmanship and unnecessary friction; but that trouble was presently overcome, for the medieval mechanic could be as fine and accurate a workman as any modern. He had the artist's personal pride and pleasure in his skill, and also a great unhurried patience, somewhat hard for us to picture in this breathless age. At best, however, his work fell far short of the accuracy possible with modern machinery. Other important difficulties were found in the expansion and contraction of parts due to temperature variations, and the fact that the foliot balance was at its best only when running slowly. Altogether, then, these early clocks were easily surpassed in accuracy of timekeeping by a sun-dial or a good clepsydra.

The question arises, therefore, why this newcomer in the field of timekeeping, should have begun to displace the earlier devices. The clock was not yet a better timepiece than the sun-dial; why did it grow more common? Well, for one thing, people like novelties. For another, people loved their churches and lived by the chimes of distant bells; and the clock was by far the most practical striking device, whatever might be its faults in keeping time. But, what was most important of all, it was a machine, susceptible of infinite improvement and offering a field for endless ingenuity. It appealed to that inborn mechanical instinct by means of which mankind has wrought his mastery over the world.

We have seen how de Vick's clock contained, as it were, the germ of all our clocks. And, moreover, the medieval regarded machinery with profoundest awe. It is the unknown which awakes imagination. We wonder at the cathedrals of his day, but the medieval knew about cathedrals; he built them. Considering their comparatively cruder tools, lack of modern hoisting machinery, and so forth, their architectural and building abilities exceeded even those of to-day. On the other hand, a locomotive or a modern watch, such as we glance at without special notice, would have appeared to him the product of sheer sorcery, too wonderful to be the work of human hands.

The Middle Ages could not much improve their clock without some radical invention; and such a mechanical type of invention was yet the province of but few minds. The typical craftsman could merely make the clock more convenient, more decorative, and more wonderful. To this work, he and his fellows addressed themselves with all of their patient skill and their endless ingenuity for ornamentation.

They made clocks for their churches and public buildings, and elaborated them with intricate mechanical devices. The old "Jacks" that struck the bells were only a beginning. They made clocks for their kings and wealthy nobles, adorning them with all the richness that an artist could design and a skilful jeweler execute. They made clocks even for ordinary domestic use so quaint in design and so clever in workmanship that we exhibit them to-day in our museums. One difficulty in determining the date of the first invention is that long before the days of de Vick and Lightfoot, machines were made to show the day of the week and month and to imitate the movements of the stars; and the first horological records may refer to clock-works of this kind.

The famous clock of Strassburg Cathedral shows the extreme to which the medieval craftsman carried this kind of ingenuity. It was originally put up in 1352 and has been twice rebuilt, each time with greater elaboration. It is three stories high and stands against the wall somewhat in the shape of a great altar with three towers. Among its movements are a celestial globe showing the positions of the sun, moon, and stars, a perpetual calendar, a device for predicting eclipses and a procession of figures representing the pagan gods from whom the days of the week are named. There are devices for showing the age and phases of the moon and other astronomical events. The hours are struck by a succession of automatic figures, and at the stroke of noon a cock, perched upon one of the towers, flaps his wings, ruffles his neck, and crows three times. This clock still remains, having last been rebuilt in the four years 1838 to 1842. But its chief interest is that of a mechanical curiosity. It keeps no better time than a common alarm-clock, nor ever did. And in beauty as well as usefulness, it has been surpassed many times by later and simpler structures.

For the first really important improvement in clock making we must pass to the latter end of the sixteenth century. The Italian Renaissance with its great impulse to art and science has come and gone, and the march of events has brought us well into the modern world. America had been discovered a century and is beginning to be colonized. Spain is trying to found a world empire upon blood and gold and the tortures of the Inquisition. England is at the height of the great Elizabethan period. It is the time of Drake and Shakespeare and Sir Walter Raleigh.

At this period of intellectual awakening, a remarkable young man steps upon the scene. In 1564, the year in which the wonderful Englishman, Shakespeare, first saw the light of day, the scarcely less wonderful Italian, Galileo, was born in Pisa. He was gifted with keen eyes and a swift, logical mind, which left its impress upon so many subjects of human thought and speculation that we are tempted to stop as with Archimedes and trace his history. But, one single incident must suffice.

Ivory and Silver Folding Dial German, Seventeenth Century

Ring Dial in general use during Sixteenth and Seventeenth Century

Ivory Compass Dial Italy, 1628

Universal Cube Dial German, Eighteenth Century

Ancestors of the Watch

Portable and pocket sun dials in the collections of the Metropolitan Museum.

In 1581, this youth of seventeen stood in the cathedral of Pisa. Close at hand, a lamp suspended by a long chain swung lazily in the air currents. There was nothing unusual in such a sight. Millions of other eyes had seen other suspended objects going through exactly this motion and had not given the sight a second thought. At this moment, however, a great discovery of far-reaching application—one which was to revolutionize clock construction—hung waiting in the air. Young Galileo took notice.

The lamp swung to and fro, to and fro. Sometimes it moved but slightly. Again, as a stronger breeze blew through the great drafty structure, it swung in a considerable arc, but always—and this was the point which impressed itself upon the Italian lad—the swing was accomplished in exactly the same time. When it moved a short distance, it moved slowly; the farther it moved, the faster became the motion; in its arc it moved more swiftly, accomplishing the long swing in the same time as it did the short one. In order to make sure of this fact, Galileo is said to have timed the swinging lamp by counting the beating of his pulse.

Thus was discovered the principle of the pendulum and its "isochronism." By "isochronism" we mean inequal arcs in equal time. In other words, any swinging body, such as a pendulum, is said to be "isochronous" when it describes long or short arcs in equal lengths of time. This also applies to a balance-wheel, and hair-spring. And herein lies a remarkable fact—this epoch-making discovery was after all but a rediscovery. The isochronism of a swinging body was known in Babylon thousands of years before, although the Babylonians, of course, could not explain it. Lacking in application, it had passed from the minds of men, and it remained for Galileo to observe the long-forgotten fact and to work out its mechanical application. He did not himself apply this principle to clock-making, although some fifty years later, toward the end of his life, he did suggest such an application.

The first pendulum clocks were probably made about 1665, by Christian Huyghens, the celebrated Dutch astronomer and mathematician who discovered the rings of Saturn; and by the English inventor, Doctor Robert Hooke. The invention is claimed for several other men in England and abroad at about the same time; but hardly upon sufficient authority.

From that time on, the important improvements of clockwork were chiefly made in two directions—those of the mechanical perfection of the escapement and the compensation for changes of temperature.

There is a little world of invention and discovery behind the face of the clock which beats so steadily on your mantel. Look within if you will, and see the compact mechanism with its toothed gears, its coiled spring, or its swinging pendulum, in which the motion of the cathedral lamp is harnessed for your service,—nothing in that grouping has merely happened so. You may or may not understand all the action of its parts, or the technical names of them; but each feature in the structure has been the result of study and experiment, as when Huyghens hung the pendulum from a separate point and connected it with a forked crank astride the pendulum shaft. You can see that forked crank to this day, if you care to look; it was the product of good Dutch brains.

Next we come to one of the greatest single improvements in clock-work, and the chief difference between the mechanism made by de Vick and the better ones of our own time. When the pallets in a clock are forced by an increased swing of the pendulum or by the form of the pallet faces against the teeth of the escape-wheel in the direction opposite to that in which the wheel is moving, the wheel must be pushed backward a little way each time, and the whole clock action is made to back up a little. You can see that this would tend to interfere with good and regular timekeeping. George Graham, in London, in 1690 corrected this error by inventing the dead-beat escapement which rather contradicted its name by working very well and faithfully.

There are many forms of this escapement and there is no need to explain it in detail. But the main idea is this: At the end of each vibration or swing of the pendulum, the escape-teeth, instead of being made to recoil by the downward motion of the pallets, simply remains stationary or at rest until the commencement of the return swing of the pendulum. This was brought about by applying certain curves to the acting faces of the pallets. But the acting faces of both tooth and pallet are beveled, so that the tooth in slipping by gives the pallet a "kick" or impulse outward and keeps it in motion. Nowadays, even a common alarm-clock has an escapement working in this way.

Then came another remarkably interesting contribution. Have you ever wondered why the pendulums of fine clocks were weighted with a gridiron of alternate rods of brass and steel? For purpose of ornament? Not at all—it constitutes a scientific solution of an embarrasing problem, due to the inevitable variations in temperature. Metals expand with heat and contract with cold. Notched iron bars can be made to "crawl" along a flat surface by alternately heating and cooling them. Bridge-builders sometimes arrange sliding points, or rocking points to adjust the differences in the length of the steel. Contraction and expansion are important factors in all their calculations. But a pendulum would change its rate of motion if it changed its length and this would interfere with its accuracy as a measurer of time. Graham worked upon this problem, too, and attached a jar of mercury to the rod of his pendulum for a weight. When the heat lengthened the rod, it also caused the mercury to rise, just as in a thermometer, and this left the "working-length" the same.

Such mercury-weighted pendulums are not uncommon to this day, but the more familiar gridiron came from the brain of John Harrison, who, in 1726, fixed the alternate rods in such a way that the expanding brass rods raised the weight as much as the expanding steel rods lowered it. Thus they neutralized each other.

The clock as we know it was now virtually complete. There were structural refinements, but no more radical improvements to be made. In tracing its development from the fourteenth to the eighteenth century, we note one curious likeness to the ancient history of recorded time. In this case, as before in Babylon, the people first concerned with the science were the priests, and after them the astronomers, but we note a still more important difference.

As the medieval passed into the modern, the practise of horology passed more and more out of the hands of scientists into the keeping of commercial workmen. The custodian of time was at first a priest, and finally a manufacturer. And this change was attended by a vast increase in the general use of timepieces, and the correspondingly greater influence of time upon society and men's way of living. The Middle Ages made clocks and watches; and clocks and watches make the age in which we live.