The Most Powerful Idea in the World

by William Rosen

  The screw is one of the canonical simple machines, along with the lever, wedge, and inclined plane, with a history dating back to the Fertile Crescent, and throughout antiquity wood screws were used as presses for oil, wine, and (by the time of the Inquisition) the occasional human thumb. Yet Maudslay sensed that the screw, despite its antiquity and simplicity, was also the tool of the future. For centuries, screws had been produced using the hand tools known as taps and dies: the former to cut interior threads—the “female” side—and the latter the exterior, or “male,” threads. But until the fifteenth century, almost all of them were cut out of wood, which didn’t do much for either their precision or their durability. Even when European metalworkers started to make metal screws, their dependence on hand tools required that the metal be relatively soft—and, more important, kept the screws rare. Until screws, and other sym-metrical metal objects, could be made by a machine, they were destined to stay that way.

  The machine that finally broke the logjam—the lathe—was nearly as old as the screw. It had evolved considerably during the preceding two millennia, from the Egyptian “rope bow” operated by a person pulling back and forth on a rope attached to the workpiece, to the Roman bow lathe, and finally to the spring-operated pole lathe, which represented the state of the art in wood turning from about the first century CE through the Middle Ages.

  Wood turning has its own satisfactions. As anyone who has ever taken what used to be called shop class will recall, there is a beauty in watching a lathe (or its close cousin, a potter’s wheel) at work. The transformation of an irregular shape into a symmetrical one seems to feed what may be a universal love of harmony, and even the simplest lathe work—turning a block of wood into a chair leg or a baseball bat—is satisfying to watch, and even more satisfying to do. But it is limiting. The lathe remained a tool for creating only beauty until the sixteenth century, when it finally became a tool for creating other tools—and, most particularly, a tool for creating metal screws.

  That was when the onetime wood turning machines acquired the mandrel—a spindle onto which the workpiece was attached, thereby transmitting rotation to the spindle rather than to the piece itself. Even more important, the sixteenth-century lathes finally started using the long leadscrew, which moved the workpiece horizontally as it was rotated. The leadscrew, combined with a steady platform for the cutting tool, was now the measure of precision in lathe work: Any piece turned on a lathe that used a leadscrew could be made as precisely as the leadscrew itself.

  Using a leadscrew made any lathe work more precise, but its really revolutionary application emerged when a number of innovators figured out how to angle the cutting head to incise a continuous helical groove onto a smooth cylinder: to machine a screw. And not just a screw fastener; the reason lathes are frequently called history’s “first self-replicating machines” is that, beginning in the sixteenth century, they were used to produce their own leadscrews. A dozen inventors from all over Europe, including the Huguenots Jacques Besson and Salomon de Caus, the Italian clockmaker Torriano de Cremona, the German military engineer Konrad Keyser, and the Swede Christopher Polhem, mastered the iterative process by which a lathe could use one leadscrew to cut another, over and over again, each time achieving a higher order of accuracy. By connecting the lathe spindle and carriage to the leadscrew, the workpiece could be moved a set distance for every revolution of the spindle; if the workpiece revolved eight times while the cutting tool was moved a single inch, then eight spiral grooves would be cut on the metal for every inch: eight turns per inch.

  Thus a leadscrew that was accurate to within ½″ could operate a lathe that could cut a new screw accurate to within 7⁄16″, and the new leadscrew could in turn produce one accurate to within ⅜″, eventually achieving a very high degree of precision.

  Not, however, high enough for Bramah’s locks. For while the leadscrews on those lathes were made of iron, most of the lathe’s other components were made of wood. And wood, even very hard wood, shakes. It shakes enough, in fact, that even the sharpest steel blade couldn’t make a cut accurate to within 1⁄16″—an enormous error margin in a three-inch lock.

  Henry Maudslay’s first, and probably greatest, contribution to the Bramah Lock Co., and to the Industrial Revolution, was his realization of the huge advantages of a lathe made entirely of iron. Not just the leadscrew and the slide rest—a platform that holds the tool post and moves the tool laterally as precisely as the leadscrew moved the workpiece horizontally—but all the platforms, bits, and supports of the lathe. Maudslay’s design integrated all of them in a manner that achieved a degree of precision greater than any could offer individually. The advantage of iron over wood turned out to be critical.

  Maudslay’s perception about the superiority of iron may have come to him in the form of a Glasgow Green sort of insight, but he left no diary that would confirm its origin, or even precisely when he produced the first all-iron lathe for Bramah, though it was certainly in operation by 1791. During the 1790s, Maudslay’s key insight—that stability equaled precision, and iron was stable—was incorporated into a number of other tools he built for Bramah’s lock business, including drills, planing machines, and possibly even a rotary file: essentially one of the first mechanical milling machines, used to shape metal into nonsymmetrical shapes, just as lathes formed them into symmetrical ones. In addition, he is credited with inventing a self-tightening leather collar that made Bramah’s hydraulic press a working proposition.

  However, Bramah was in the business of selling locks, not lathes, and he determined that the best business decision was to patent the things made by his new machine tools, not the tools themselves, which he kept secret as long as possible; as a result, it is rather difficult to document when, precisely, Maudslay and Bramah put them on the company’s production line. No such problem exists in documenting Maudslay’s devotion to his employer, which was far greater than his employer had for him. Even when Bramah promoted Maudslay3 to shop superintendent in 1798, he was still paying him a fairly modest thirty shillings a week, which was not enough for Maudslay’s growing family. Unable to persuade Bramah4 to part with a living wage, Maudslay left and set up shop on Oxford Street in London, where he was employing eighty men by 1800, and nearly two hundred by 1810.

  And still he remained obsessed with screws and screw-making machinery.* Maudslay rightly realized that the match of screw lands to bolts or receivers was key to fastening metal pieces in large machines as well as small, and that the large machines represented a far more profitable market. He spent the decade after leaving Bramah building lathes that could produce screws of any desired pitch using the same leadscrew, and that were both large enough to make the linkage for a 48-inch cylinder steam engine and precise enough to make the quarter-inch valves that controlled their operation.

  The key was the leadscrew, which reproduced its exact pitch on the material to be threaded—and introduced exactly the same inaccuracies. If the leadscrew was accurate to (for example) ¼″, then the screw, or screw fitting, it cut might make eight turns in anything from ⅞″ to 1⅛″; if it was accurate to 1⁄16″, then its fittings would make the same eight turns somewhere between 31⁄32″ and 11⁄32″. Ten years of experimentation with different combinations of gears and cutting tools eventually resulted in a seven-foot-long brass leadscrew that was accurate to within less than 1⁄16″.

  By then, however, 1⁄16″ might as well have been a foot; in another example of one problem’s solution creating a new set of problems, the more accuracy Maudslay had, the more he needed. This was because, while he was iterating his way to his prize leadscrew, he had also built himself a tool that was to eighteenth-century metalworking what Galileo’s telescope was to fifteenth-century astronomy. Perhaps unsurprisingly, the tool was used not to make things, but to measure them.

  Micrometers, devices for measuring very small increments, were then only about thirty years old; James Watt himself had produced what was probably the world’s first in
1776, a horizontal scale marked with fine gradations and topped with two jaws, one fixed and the other moved horizontally by turning a screw. With a pointer on the movable jaw, objects could be measured extremely accurately, up to 1⁄100″. But Maudslay’s micrometer, which he nicknamed “the Lord Chancellor,” was capable of measuring differences of less than 1⁄1000″ (some say 1⁄10,000″). When he measured the seven-foot-long brass screw, inch by inch, with the Lord Chancellor, he found that his “perfect” screw was actually inconsistent along its entire length: one inch might have fifty threads, another fifty-one, a third forty-nine, and the only reason it seemed accurate was that the irregularities had canceled one another out. This was clearly unsatisfactory to a perfectionist of Maudslay’s degree, and the screw was recut, again and again, until even the Lord Chancellor could find no error.

  There is a mythic quality to the Lord Chancellor—an Excalibur of measurement, slaying the dragon of imprecision—that explains its ubiquity in stories about Maudslay and his entire era. But that very quality tends to hide its real importance. The Industrial Revolution, however it is defined, depended on Maudslay’s micrometer, and instruments like it, just as much as it did on laws protecting intellectual property or the birth of scientific experimentation. This is because sustained innovation is incremental innovation, and those increments are usually very small: a valve that weighs a fraction of an ounce less, a linkage that reduces coal consumption by a few pounds a day. Without instruments that could measure such small improvements in performance, invention was doomed to be rare and erratic; the mania for precision that was Maudslay’s defining characteristic made it commonplace.

  Maudslay’s own inventions are impressive enough. In 1805, he patented a machine that could print designs on cotton; in 1806, he invented a new method for lifting weights with a differential motion; and in 1807, he devised a new and compact framework for supporting the cylinder of a steam engine, which permitted the use of so-called “table engines” in far smaller factory areas.

  His influence is, however, larger than that, beginning with the astonishing number of other equally obsessive engineer-inventors to whom he was teacher and mentor. The best known may be the almost embarrassingly prolific Richard Roberts, who acquired patents the way Balzac wrote novels.* Another of Maudslay’s assistants, Joseph Whitworth, developed a measuring system accurate to one-millionth of an inch. This is not a misprint; until the United Kingdom joined the metric system, the standard unit for screw threads was the BSW, which stands for British Standard Whitworth.

  Whitworth worked for Maudslay at the same time as Joseph Clement, who would later build, on the instructions of Charles Babbage, the prototype for the original “difference engine”—the world’s first mechanical computer. Maudslay’s son, Joseph, later became a brilliant marine engineer, patenting the double-cylinder marine engine that was widely used during the nineteenth century. Yet another Maudslay graduate, James Nasmyth, the inventor of a steam hammer that made him the wealthiest of them all, wrote floridly of his mentor, “the indefatigable care which he took5 in inculcating and diffusing among his workmen, and mechanical men generally, sound ideas of practical knowledge, and refined views of construction, has rendered, and ever will continue to render, his name identified with all that is noble in the ambition of a lover of mechanical perfection.” More prosaically, though probably just as accurately, one of Maudslay’s workmen remembered that “it was a pleasure to see him handle a tool6 of any kind, but he was quite splendid with an 18 inch file.”

  However, even if Maudslay had never built an iron lathe to make Bramah his locks, never become the era’s icon of precision, or never turned his Oxford Street workshop into the place where, as one modern historian put it, “a ‘critical mass’ of inventive activity”7 was achieved, he would still have earned a large place in industrial history. And he would have earned it by building blocks.

  A PILGRIMAGE TO BRITAIN’S sacred sites of industrialism would certainly include Boulton & Watt’s Soho Foundry and the Ironbridge Gorge Museums; probably the four-hundred-foot-deep mine at the National Coal Mining Museum in Yorkshire; and possibly the pumping station at Crofton. It would certainly be incomplete without a visit to the eastern shore of Portsmouth Harbor, where the Royal Navy’s largest dockyard houses museums, historically important ships, and the Portsmouth Block Mills,* the place where Henry Maudslay’s machines would make up the world’s first true steam-powered factory.

  The quadrupling of the Royal Navy during the eighteenth century, like the Apollo space program of the 1960s, created a massive customer for technological innovation. This was, after all, the Age of Sail, and while guns and ammunition might be metal, getting those guns to where they could be useful required the pressure of wind on canvas. Wind was a useful source of power for mills, but its directional variability made it a capricious sort of transportation “fuel,” and a staggering amount of human ingenuity was required to make the wind blowing this way drive a three-thousand-ton ship that way. Each sail—a three-masted ship had at least nine—was raised, lowered, reefed, and turned by some portion of more than twenty miles of rope, every foot of which ran through up to a dozen different pulleys, contained within blocks of wood. The blocks consisted of shells, usually of elm, cut with several oblong slots, or mortises, each containing a hardwood pulley fitted with metal bushings spinning around a pin, usually made of iron. A single ship of the line8 required as many as fifteen hundred such blocks, ranging in length from three inches to three feet, and with nearly a thousand ships at sea by the beginning of the nineteenth century, wearing out their blocks at a rapid rate, anyone who could produce them in quantity was going to make an indecent amount of money doing so; in 1800, the navy was paying more than 8 guineas—two months of a skilled laborer’s salary—for a single 38-incher.

  For centuries, blocks—shell, pulley, and pin—had been made by hand, with all the cost in time and error that implied. The first block makers to mechanize were the Walter Taylors (father and son) in 1754; eight years later, they patented their “Set of engines, tools, instruments,9 and other apparatus for the Making of Blocks, Sheavers, and Pins.” In 1786 they received another, for lubricating the apparatus. More significant was Samuel Bentham,10 whose 1793 patent for woodworking machinery included a rotary planer; a circular saw; a primitive router for dovetail grooving; bevel saws, crown saws, and radial saws; radial and reciprocating mortise machines; guides, grinders, gauges, and tables; and his own version of the slide rest lathe. The Bentham application was so frighteningly comprehensive, covering all conceivable aspects of mechanized woodworking, that the Patent Office regarded it as “a perfect treatise on the subject.”11

  An innovative naval officer determined to reform his tradition-minded service, Bentham had become fascinated by the potential for machine production of naval components largely by accident. In 1786, while in Russia,12 where he had gone to take a job as a naval engineer, he was so short of skilled craftsmen that the only way to produce blocks, tackles, belaying pins, and all the other wooden impedimenta of the Age of Sail was to make the process simple enough that they could be manufactured by even illiterate and untrained serfs. Or, even better, by machines.

  Bentham’s older brother, the political philosopher Jeremy, had independently developed an interest in woodworking by unskilled laborers. While he is best remembered for his utilitarian philosophy—“the greatest good for the greatest number”—Jeremy Bentham probably spent as much time thinking about prison reform as anything else,* and his fascination with prisons extended to the idea that woodworking was the perfect way to occupy the idle but untrained hands of prisoners.

  In 1795, the Bentham brothers put their ideas together and drafted a contract proposing that the Admiralty use prison labor to operate the woodworking machines used to produce naval stores. Jeremy, evidently ambitious to find an even larger market for Samuel’s inventions, wrote a letter to his friend, the Duc de la Rochefoucauld, a French nobleman then in exile in North America, asking wh
ether “a Propos of my brother’s inventions,13 do you know of anybody where you are … who would like to be taught how to stock all North America with all sorts of woodwork … on the terms of allowing the inventor [i.e. Samuel] a share of the profits as they arise?” The Frenchman evidently had no immediate help on offer, but a few years later, the letter was apparently the chief subject of discussion at a dinner party in New York City, whose guests included the recently resigned secretary of the Treasury, Alexander Hamilton, and another French émigré, a former sailor and engineer named Marc Isambard Brunel.

  BRUNEL HAD BY THEN crowded a fair bit into his first twenty-seven years. When he was eleven, he traveled from his birthplace at Haqueville in Normandy to attend the seminary of St. Nazaire in Rouen, where soon enough the priests realized that the boy’s vocation was more mechanical than pastoral. They sent him to live with the American consul in Rouen, a retired sea captain, to be educated in hydrography and drafting as preparation for a naval career. He was commissioned into the French Navy in 1786 and served on a dozen voyages, but when he returned from the West Indies in 1792, France’s three-year-old revolution was taking a violent turn. In the fall, Parisians had imprisoned the king and queen, and the era of mass executions known as the Reign of Terror was looming. Brunel decided to emigrate. His education seems to have nurtured interests in navigation and the United States of America equally; a year later, in September 1793, he landed in New York.