Longitude

by Dava Sobel

  The Frenchman, the sieur de St. Pierre, frowned on the moons of Jupiter as a means of determining longitude, though they were all the rage in Paris. He put his personal faith in the guiding powers of Earth’s moon, he said. He proposed to find longitude by the position of the moon and some select stars—much as Johannes Werner had suggested one hundred sixty years previously. The king found the idea intriguing, so he redirected the efforts of his royal commissioners, who included Robert Hooke, a polymath equally at home behind a telescope or a microscope, and Christopher Wren, architect of St. Paul’s Cathedral.

  For the appraisal of St. Pierre’s theory, the commissioners called in the expert testimony of John Flamsteed, a twenty-seven-year-old astronomer. Flamsteed’s report judged the method to be sound in theory but impractical in the extreme. Although some passing fair observing instruments had been developed over the years, thanks to Galileo’s influence, there was still no good map of the stars and no known route for the moon.

  Flamsteed, with youth and pluck on his side, suggested that the king might remedy this situation by establishing an observatory with a staff to carry out the necessary work. The king complied. He also appointed Flamsteed his first personal “astronomical observator”— a title later changed to astronomer royal. In his warrant establishing the Observatory at Greenwich, the king charged Flamsteed to apply “the most exact Care and Diligence to rectifying the Tables of the Motions of the Heavens, and the Places of the fixed Stars, so as to find out the so-much desired Longitude at Sea, for perfecting the art of Navigation.”

  In Flamsteed’s own later account of the turn of these events, he wrote that King Charles “certainly did not want his ship-owners and sailors to be deprived of any help the Heavens could supply, whereby navigation could be made safer.”

  Thus the founding philosophy of the Royal Observatory, like that of the Paris Observatory before it, viewed astronomy as a means to an end. All the far-flung stars must be cataloged, so as to chart a course for sailors over the oceans of the Earth.

  Commissioner Wren executed the design of the Royal Observatory. He set it, as the king’s charter decreed, on the highest ground in Greenwich Park, complete with lodging rooms for Flamsteed and one assistant. Commissioner Hooke directed the actual building work, which got under way in July of 1675 and consumed the better part of one year.

  Flamsteed took up residence the following May (in a building still called Flamsteed House today) and collected enough instruments to get to work in earnest by October. He toiled at his task for more than four decades. The excellent star catalog he compiled was published posthumously in 1725. By then, Sir Isaac Newton had begun to subdue the confusion over the moon’s motion with his theory of gravitation. This progress bolstered the dream that the heavens would one day reveal longitude.

  Meanwhile, far from the hilltop haunts of astronomers, craftsmen and clockmakers pursued an alternate path to a longitude solution. According to one hopeful dream of ideal navigation, the ship’s captain learned his longitude in the comfort of his cabin, by comparing his pocket watch to a constant clock that told him the correct time at home port.

  4.

  Time in a Bottle

  There being no mystic communion of clocks

  it hardly matters when this autumn breeze

  wheeled down from the sun

  to make leaves skirt pavement like a

  million lemmings.

  An event is such a little piece of time-and-space

  you can mail it through the slotted eye of the cat.

  —DIANE ACKERMAN, “Mystic Communion of Clocks”

  Time is to clock as mind is to brain. The clock or watch somehow contains the time. And yet time refuses to be bottled up like a genie stuffed in a lamp. Whether it flows as sand or turns on wheels within wheels, time escapes irretrievably, while we watch. Even when the bulbs of the hourglass shatter, when darkness withholds the shadow from the sundial, when the mainspring winds down so far that the clock hands hold still as death, time itself keeps on. The most we can hope a watch to do is mark that progress. And since time sets its own tempo, like a heartbeat or an ebb tide, timepieces don’t really keep time. They just keep up with it, if they’re able.

  Some clock enthusiasts suspected that good timekeepers might suffice to solve the longitude problem, by enabling mariners to carry the home-port time aboard ship with them, like a barrel of water or a side of beef. Starting in 1530, Flemish astronomer Gemma Frisius hailed the mechanical clock as a contender in the effort to find longitude at sea.

  “In our times we have seen the appearance of various small clocks, capably constructed, which, for their modest dimensions, provide no problem to those who travel,” Frisius wrote. He must have meant they provided no problem of heft or high price to rich travelers; certainly they did not keep time very well. “And it is with their help that the longitude can be found.” The two conditions that Frisius spelled out, however— namely, that the clock be set to the hour of departure with “the greatest exactness” and that it not be allowed to run down during the voyage—virtually ruled out any chance of applying the method at that time. The clocks of the early sixteenth century weren’t equal to the task. They were neither accurate nor able to run true against the assault of changing temperature on the high seas.

  Although it is not clear whether he knew of Gemma Frisius’s suggestion, William Cunningham of England revived the timekeeper idea in 1559, recommending watches “such as are brought from Flanders” or found “without Temple barre,” right in London, for the purpose. But these watches typically gained or lost as many as fifteen minutes a day, and thus fell far short of the accuracy required to determine one’s whereabouts. (Multiplying a difference in hours by fifteen degrees gives only an approximation of location; one also needs to divide the number of minutes and seconds by four, to convert the time readings to degrees and minutes of arc.) Nor had timepieces enjoyed any significant advances by 1622, when English navigator Thomas Blundeville proposed using “some true Horologie or Watch” to determine longitude on transoceanic voyages.

  The shortcomings of the watch, however, failed to squelch the dream of what it might do once perfected.

  Galileo, who, as a young medical student, successfully applied a pendulum to the problem of taking pulses, late in life hatched plans for the first pendulum clock. In June of 1637, according to Galileo’s protégé and biographer, Vincenzo Viviani, the great man described his idea for adapting the pendulum “to clocks with wheelwork for assisting the navigator to determine his longitude.”

  Legends of Galileo recount an early mystical experience in church that fostered his profound insights about the pendulum as timekeeper: Mesmerized by the to-and-fro of an oil lamp suspended from the nave ceiling and pushed by drafts, he watched as the sexton stopped the pan to light the wick. Rekindled and released with a shove, the chandelier began to swing again, describing a larger arc this time. Timing the motion of the lamp by his own pulse, Galileo saw that the length of a pendulum determines its rate.

  Galileo always intended to put this remarkable observation to work in a pendulum clock, but he never got around to building one. His son, Vincenzio, constructed a model from Galileo’s drawings, and the city fathers of Florence later built a tower clock predicated on that design. However, the distinction for completing the first working pendulum clock fell to Galileo’s intellectual heir, Christiaan Huygens, the landed son of a Dutch diplomat who made science his life.

  Huygens, also a gifted astronomer, had divined that the “moons” Galileo observed at Saturn were really a ring, impossible as that seemed at the time. Huygens also discovered Saturn’s largest moon, which he named Titan, and was the first to notice markings on Mars. But Huygens couldn’t be tied to the telescope all the time. He had too many other things on his mind. It is even said that he chided Cassini, his boss at the Paris Observatory, for the director’s slavish devotion to daily observing.

  Huygens, best known as the first great horologist, swore he
arrived at the idea for the pendulum clock independently of Galileo. And indeed he evinced a deeper understanding of the physics of pendulum swings—and the problem of keeping them going at a constant rate—when he built his first pendulum-regulated clock in 1656. Two years later Huygens published a treatise on its principles, called the Horologium, in which he declared his clock a fit instrument for establishing longitude at sea.

  By 1660, Huygens had completed not one but two marine timekeepers based on his principles. He tested them carefully over the next several years, sending them off with cooperative sea captains. On the third such trial, in 1664, Huygens’s clocks sailed to the Cape Verde Islands, in the North Atlantic off the west coast of Africa, and kept good track of the ship’s longitude all the way there and back.

  Now a recognized authority on the subject, Huygens published another book in 1665, the Kort Onderwys, his directions for the use of marine timekeepers. Subsequent voyages, however, exposed a certain finickiness in these machines. They seemed to require favorable weather to perform faithfully. The swaying of the ship on a storm’s waves confounded the normal swinging of the pendulum.

  To circumvent this problem, Huygens invented the spiral balance spring as an alternative to the pendulum for setting a clock’s rate, and had it patented in France in 1675. Once again, Huygens found himself under pressure to prove himself the inventor of a new advance in timekeeping, when he met a hot-blooded and headstrong competitor in the person of Robert Hooke.

  Hooke had already made several memorable names for himself in science. As a biologist studying the microscopic structure of insect parts, bird feathers, and fish scales, he applied the word cell to describe the tiny chambers he discerned in living forms. Hooke was also a surveyor and builder who helped reconstruct the city of London after the great fire of 1666. As a physicist, Hooke had his hand in fathoming the behavior of light, the theory of gravity, the feasibility of steam engines, the cause of earthquakes, and the action of springs. Here, in the coiled contrivance of the balance spring, Hooke clashed with Huygens, claiming the Dutchman had stolen his concept.

  The Hooke-Huygens conflict over the right to an English patent for the spiral balance spring disrupted several meetings of the Royal Society, and eventually the matter was dropped from the minutes, without being decided to either contestant’s satisfaction.

  In the end, there was no end to the strife, though neither Hooke nor Huygens produced a true marine timekeeper. The separate failures of these two giants seemed to dampen the prospects for ever solving the longitude problem with a clock. Disdainful astronomers, still struggling to amass the necessary data required to employ their lunar distance technique, leaped at the chance to renounce the timekeeper approach. As far as they could see, the answer would come from the heavens—from the clockwork universe and not from any ordinary clock.

  5.

  Powder of Sympathy

  The College will the whole world measure;

  Which most impossible conclude,

  And Navigation make a pleasure

  By finding out the Longtitude.

  Every Tarpaulin shall then with ease

  Sayle any ship to the Antipodes.

  —ANONYMOUS (ABOUT 1660) “Ballad of Gresham College”

  At the end of the seventeenth century, even as members of learned societies debated the means to a longitude solution, countless cranks and opportunists published pamphlets to promulgate their own harebrained schemes for finding longitude at sea.

  Surely the most colorful of the offbeat approaches was the wounded dog theory, put forth in 1687. It was predicated on a quack cure called powder of sympathy. This miraculous powder, discovered in southern France by the dashing Sir Kenelm Digby, could purportedly heal at a distance. All one had to do to unleash its magic was to apply it to an article from the ailing person. A bit of bandage from a wound, for example, when sprinkled with powder of sympathy, would hasten the closing of that wound. Unfortunately, the cure was not painless, and Sir Kenelm was rumored to have made his patients jump by powdering—for medicinal purposes—the knives that had cut them, or by dipping their dressings into a solution of the powder.

  The daft idea to apply Digby’s powder to the longitude problem follows naturally enough to the prepared mind: Send aboard a wounded dog as a ship sets sail. Leave ashore a trusted individual to dip the dog’s bandage into the sympathy solution every day at noon. The dog would perforce yelp in reaction, and thereby provide the captain a time cue. The dog’s cry would mean, “the Sun is upon the Meridian in London.” The captain could then compare that hour to the local time on ship and figure the longitude accordingly. One had to hope, of course, that the powder really held the power to be felt many thousand leagues over the sea, and yet—and this is very important—fail to heal the telltale wound over the course of several months. (Some historians suggest that the dog might have had to be injured more than once on a major voyage.)

  Whether this longitude solution was intended as science or satire, the author points out that submitting “a Dog to the misery of having always a Wound about him” is no more macabre or mercenary than expecting a seaman to put out his own eye for the purposes of navigation. “[B]efore the Back-Quadrants were Invented,” the pamphlet states, “when the Forestaff was most in use, there was not one Old Master of a Ship amongst Twenty, but what a Blind in one Eye by daily staring in the Sun to find his Way.” This was true enough. When English navigator and explorer John Davis introduced the backstaff in 1595, sailors immediately hailed it as a great improvement over the old cross-staff, or Jacob’s staff. The original sighting sticks had required them to measure the height of the sun above the horizon by looking directly into its glare, with only scant eye protection afforded by the darkened bits of glass on the instruments’ sighting holes. A few years of such observations were enough to destroy anyone’s eyesight. Yet the observations had to be made. And after all those early navigators lost at least half their vision finding the latitude, who would wince at wounding a few wretched dogs in the quest for longitude?

  A much more humane solution lay in the magnetic compass, which had been invented in the twelfth century and become standard equipment on all ships by this time. Mounted on gimbals, so that it remained upright regardless of the ship’s position, and kept inside a binnacle, a stand that supported it and protected it from the elements, the compass helped sailors find direction when overcast skies obscured the sun by day or the North Star at night. But the combination of a clear night sky and a good compass together, many seamen believed, could also tell a ship’s longitude. For if a navigator could read the compass and see the stars, he could get his longitude by splitting the distance between the two north poles—the magnetic and the true.

  The compass needle points to the magnetic north pole. The North Star, however, hovers above the actual pole—or close to it. As a ship sails east or west along any given parallel in the northern hemisphere, the navigator can note how the distance between the magnetic and the true pole changes: At certain meridians in the mid-Atlantic the intervening distance looks large, while from certain Pacific vantage points the two poles seem to overlap. (To make a model of this phenomenon, stick a whole clove into a navel orange, about an inch from the navel, and then rotate the orange slowly at eye level.) A chart could be drawn—and many were—linking longitude to the observable distance between magnetic north and true north.

  This so-called magnetic variation method had one distinct advantage over all the astronomical approaches: It did not depend on knowing the time at two places at once or knowing when a predicted event would occur. No time differences had to be established or subtracted from one another or multiplied by any number of degrees. The relative positions of the magnetic pole and the Pole Star sufficed to give a longitude reading in degrees east or west. The method seemingly answered the dream of laying legible longitude lines on the surface of the globe, except that it was incomplete and inaccurate. Rare was the compass needle that pointed precisely north at all ti
mes; most displayed some degree of variation, and even the variation varied from one voyage to the next, making it tough to get precise measurements. What’s more, the results were further contaminated by the vagaries of terrestrial magnetism, the strength of which waxed or waned with time in different regions of the seas, as Edmond Halley found during a two-year voyage of observation.

  In 1699, Samuel Fyler, the seventy-year-old rector of Stockton, in Wiltshire, England, came up with a way to draw longitude meridians on the night sky. He figured that he—or someone else more versed in astronomy—could identify discrete rows of stars, rising from the horizon to the apex of the heavens. There should be twenty-four of these star-spangled meridians, or one for each hour of the day. Then it would be a simple matter, Fyler supposed, to prepare a map and timetable stating when each line would be visible over the Canary Islands, where the prime meridian lay by convention in those days. The sailor could observe the row of stars above his head at local midnight. If it were the fourth, for argument’s sake, and his tables told him the first row should be over the Canaries just then, assuming he had some knowledge of the time, he could figure his longitude as three hours—or forty-five degrees—west of those islands. Even on a clear night, however, Fyler’s approach invoked more astronomical data than existed in all the world’s observatories, and its reasoning was as circular as the celestial sphere.