The Technology of Machinery
The Technology of Machinery
Mechanical Marvels. While medieval Europeans professed the desire to emulate Rome (or rather their idealized vision of it), their worldview had changed to such a degree that in striving to achieve their goal, they inadvertently took another, more impressive, course and created a world that in many ways surpassed their model. Not only did they harness animals, wind, and water, and build monumental structures in entirely new forms, but they also created objects that surpassed those of the Romans in their intricacy and subtlety. It has been said that Rome marshaled great masses to provide great forces to create great constructions—for instance, the Coliseum or the Pantheon. Medieval Europeans took a different route: they marshaled mechanical ingenuity to do more with less labor. By the end of the Middle Ages, Europe was filled with mechanical marvels that ancient Romans had never thought possible.
Origins. The genesis of medieval mechanical innovation appears to be the inventions that improved medieval millers’ ability to exploit water and wind power. In particular, the shift from horizontal mills to vertical mills required a set of gears to transmit power from the horizontally rotating shaft of the waterwheel or the sails to the vertically rotating shaft of the millstone. These gears allowed rotary motion to be transmitted and used for many purposes, from grinding and polishing to boring and rolling. In addition, medieval engineers learned that a rotating shaft could produce more than just rotational motion. Medieval Europeans were apparently the first society to understand the concept of the—deceptively simple—crank, which is documented in the Utrecht Psalter (820), which includes an illustration of a sword-sharpening grindstone. They soon realized that, not only can a crank be used to turn a wheel, but so too will a rotating wheel turn a crank—and, with the appropriate linkages, that rotating crank can change a rotational motion into a reciprocating (back-and-forth) motion that can be used for such things as sawing wood.
Worm Gears, Cams, and Levers. They next discovered that they could use regular gears with what came to be known as worm gears (wheels whose teeth mesh with the threads of short screws) to magnify greatly the force, or torque, of gear assemblies. They found that, if a pair of gears—each of which had teeth around only one-half of its circumference—is connected to a central main gear (with
MEDIEVAL TIME TELLING
In his “Parson’s Tale,” written during the last quarter of the fourteenth century, Geoffrey Chaucer mentioned four of the many different ways to tell that it was about 4 P.M. when the “Manciple’s Tale” ended and his pilgrims entered a village for the evening: by the elevation of the setting sun, by the clock, by the length of his shadow, jind by the zodiacal position of the moon.
What time the manciple his tale had ended,
The sun down from the south line had descended
Solow that he was not, unto my sight,
Degrees full nine and twenty yet in height.
Four of the clock it was then, as I guess:
Four feet eleven, little moreor less,
My shadow was extended then and there,
A length as if the shadow parted were
In six-foot equal parts, as I have shown.
Therewith the moon’s high exaltation known,
I mean the sign of Libra, did ascend
As we were entering a village-end.
Source: Linne R. Mooncy, “The Cock and the Clock: Telling Time Chaucer’s Day,” Studies’in the Age ofChaucer, 15 (1993): 91–109.
all its teeth), axles can be made rotate one way and then the other, while the main axle maintains a constant rotation in one direction. They also learned that if a short projection, called a cam, is placed on a rotating shaft, each time the shaft comes around the projection will strike or trip some other machine part. Cams are remarkably powerful, and the combination of a cam and a lever allowed medieval technicians to turn the small motion of the cam into a large motion that could operate a tool such as a hammer head or a stamp, as well as the delicate motion needed to strike a bell. While the crank provided continuous reciprocal motion, the cam allowed intermittent motion. With this development, the door was opened for the invention of all sorts of machines.
Machinery at Work. Once medieval Europeans understood gears, levers, cranks, and cams, they could do much more than using mills to grind grain. Appropriately outfitted mills crushed ore for mining, pumped water for drainage and irrigation, cut wood and stone for construction, pumped bellows for smithies and foundries, hoisted construction materials at building sites, and raised actors through the floors of stages, and above, for dramatic effect. For the first time in human history, a civilization was built first and foremost by machinery, not primarily by human labor (though it still played a significant role).
Clocks . Medieval craftsmen also designed fine machinery to perform precise tasks. From the astrolabe to measure the positions of heavenly bodies as an aid to navigation, to the mechanical clock to mark time, medieval technologists learned and refined the art of precision engineering. Initially, nearly every society marked time in a different way, but today the standard measures of seconds, minutes, hours, and days are used worldwide. That uniformity is a legacy from medieval Europeans, the first society to develop a reliable mechanical timekeeper, which in turn established the equal hours, minutes, and seconds system.
Variable Time. Each day is, of course, divided into day and night, and from ancient times one way to subdivide day and night was into twelve units each: twelve hours of daylight and twelve hours of darkness. (This same base is the reason there are twelve signs of the zodiac.) The periods of daylight and darkness in a day, however, vary in length: as one travels farther and farther from the equator during summer, daylight lasts longer and longer, while the opposite is true in winter. If one uses a “variable hour” system, marking off twelve hours of light and twelve hours of darkness, a daylight hour in June in London is a great deal longer than a daylight hour in December in the same city. Thus, the amount of time in a variable “hour” changes with the seasons.
Keeping Variable Time. Before and during the Middle Ages the unequal-hour time system worked just fine for most purposes. Though sundials that measure equal hours summer or winter came into use late in the Middle Ages, for most of the period those in use since antiquity divided daylight hours, regardless of their length, into twelve parts. The most common form of timekeeper in antiquity and the early Middle Ages was a water clock, or clepsydra, which allows water to drip at a regular rate into a collection vessel. A given amount of water equals a specific amount of time. Water clocks could easily be adjusted to allow for variable hours as the seasons changed. For the majority of society there was no reason to know the time during the night. For agriculture or business, daily tasks were completed as natural light allowed; meetings were scheduled for whenever a certain sun time came around, and life went on as usual.
Telling Time at Night. Astronomers, however, liked to divide the day-night cycle into twenty-four equal parts because it made their calculations easier, and the monastic clergy needed a device that told time during the dark hours as well during daylight. Christian liturgy requires specific prayers to be said in a certain sequence at the “canonical hours”—Matins (midnight), Prime (6:00 A.M.), Terce (9:00 A.M.), Sext (noon), None (3:00 P.M.), Vespers (6:00 P.M.), and Compline, said at nightfall. In monasteries this routine cycles of prayers punctuated the entire twenty-four-hour day, and the first mechanical clocks seem to have been developed as alarms to awaken the brethren for prayers in the night. The name clock derives from the German word Glocke (bell), and, even before mechanical clocks were developed, there are records of water clocks with mechanisms designed to ring alarm bells. Few of these had dials; apparently they were meant only to sound an alarm.
Mechanical Clocks. The first clocks that dispensed with water or another dripping fluid and used a mechanism made of gears and levers to mark the passage of time
appeared in the early fourteenth century. Documents from about that time show clockwork mechanisms with intricate and complex configurations. These clocks divide the day into twenty-four hours, but that function was secondary; their main purpose was to display the motions of the stars and the known planets. Many, though not all, were connected to bell-ringing machinery that could strike bells the appropriate number of times to mark each passing hour. Because the clock was made partly as a sounding device and partly as an aid to astronomers, the counting of the hours was done according to the astronomers’ system of twenty-four equal hours per day-night, regardless of the season.
The Clock Mechanism. A simple mechanical clock consists of a weight on a cord that is wrapped around an axle. As the weight is pulled downward by gravity, it turns the axle. The heart of the clock is an ingenious device that slows and regulates the fall of the weight. This “escapement,” or timing mechanism, consists of a horizontal bar called a “foliot” turning a vertical shaft called a “verge” (staff or rod) with two “pallets,” which are much like the cams used to strike or trip other machine parts in mills. The pallets are pushed one way and then another by the top and bottom teeth of a large saw-toothed gear called the crown wheel. As each tooth catches a pallet, it pushes on it and forces the foliot to swing backward. But this means that the opposing pallet catches the next tooth on the opposite side, reversing the original impulse. The foliot oscillates back and forth, and because reversing direction takes force and therefore time, the verge allows the crown wheel to rotate only in small, even, methodical steps. The driving weight, connected through a series of gears to the crown wheel, “falls” in small increments as the verge and foliot escapement permits, so slowly one can scarcely see it move. Small weights could be added on the arms of the foliot to regulate the oscillation. The heavier these weights, or the farther out the arms they were placed, the longer it took for each oscillation. The clockwork mechanism was fairly easy to adjust so that it would keep time with the stars and the planets, but it was quite difficult to readjust the foliot on a daily basis to make the clock speed up or slow down as the days grew shorter or longer. The clock, in other words, failed to keep time the way most people had kept time for centuries, and instead made the astronomers’ method of telling time the standard for everyone.
Astronomical Clocks. Natural philosophers quickly realized the connection between this worldly signifier of time and the phenomena it was designed to signify: the movements of the heavens. Within a few decades of the first recorded mechanical clocks, two exceedingly complex clocks—one in England and another in Italy—were documented. Richard of Wallingford, an English abbot and philosopher, left a manuscript, dating from roughly 1333, that describes in great detail the construction of an astronomical clockwork mechanism for the monastery of St. Albans. Some thirty years later, Giovanni de’Dondi of Padua also built an astronomical clock and wrote a book describing this “astrarium.” Both these machines were amazingly complex: each traced the motions of the sun, the moon, the five known planets, and the so-called fixed stars, as well as displaying the dates of the fixed Church holy days (such as Christmas) and the movable feasts (such as Easter). These clocks were famous far and wide in their day.
Adapting to Clock Time. Equal hours might still have remained an astronomer’s special way of time telling, but for the exceptional popularity of the mechanical clock. In less than a century, weight-driven clocks spread to all the cities and most of the important towns of Europe. These new clocks spread because they were easier to build than water clocks and were readily adapted to spaces large and small, high in the church tower or in the houses of the wealthy. Sundials remained in use, but clocks, conspicuously mounted on church and urban towers (where public sundials had been mounted) as a sign of pride, more and more frequently chimed out the equal hours. In fact, sundial makers developed a complex way to make sundial time approximate the equal hours of mechanical clocks.
Hourglasses. Daily life was increasingly regulated by clocks as well. Although clock faces were still not altogether standard or common, and accurate telling of minutes did not come for more than a century, late medieval Europeans told time by the bell (the meaning of “o’clock” in English). One sign of this shift is found in the spread of the common sandglass or hourglass. Sandglasses could have been invented at any time, but none have been found that date before advent the mechanical clock in the fourteenth century. People turned their glasses when the bell sounded the start of an hour and then referred to the state of the sand to give them an approximate indication of the time until the next bell was struck. Sandglasses were made in sets—hour, half hour, and quarter hour—and many regulations limited activities according to the sandglass. Preachers, university lecturers, committees, lawyers arguing cases, and even torturers “examining” their victims were all subject to a new time discipline grounded in the sounding of the clock bell and the slipping of the sand in the hourglass.
Gehard Dohrn-van Rossum, History of the Hour: Clocks and Modern Temporal Orders (Chicago: University of Chicago Press, 1996).
Giovanni de’Dondi, Mechanical Universe: The Astrarium of Giovanni de’Dondi, edited and translated by Silvio Bedini and Francis Maddi-son, Transactions of the American Philosophical Society, new series 56, part 5 (Philadelphia: American Philosophical Society, 1966).
Richard of Wallingford, Richard of Wallingford: An Edition of His Writings, 3 volumes, edited and translated by John D. North (Oxford: Oxford University Press 1976).
Lynn Townsend White Jr., Medieval Religion and Technology: Collected Essays (Berkeley: University of California Press, 1978).