by Dava Sobel
Admiral Shovell’s disastrous multishipwreck on the Scilly Isles after the turn of the eighteenth century intensified the pressure to solve the longitude problem.
Two infamous entrants into the fray in the aftermath of this accident were William Whiston and Humphrey Ditton, mathematicians and friends, who often engaged each other in wide-ranging discussions. Whiston had already succeeded his mentor, Isaac Newton, as Lucasian professor of mathematics at Cambridge—and then lost the post on account of his unorthodox religious views, such as his natural explanation for Noah’s flood. Ditton served as master of the mathematics school at Christ’s Hospital, London. In a long afternoon of pleasant conversation, this pair hit on a scheme for solving the longitude problem.
As they later reconstructed the train of their thought in print, Mr. Ditton reasoned that sounds might serve as a signal to seamen. Cannon reports or other very loud noises, intentionally sounded at certain times from known reference points, could fill the oceans with audible landmarks. Mr. Whiston, concurring heartily, recalled that the blasts of the great guns fired in the engagement with the French fleet off Beachy Head, in Sussex, had reached his own ears in Cambridge, some ninety miles away. And he had also learned, on good authority, that explosions from the artillery of the Dutch Wars carried to “the very middle of England, at a much greater distance.”
If enough signal boats, therefore, were stationed at strategic points from sea to sea, sailors could gauge their distance from these stationary gun ships by comparing the known time of the expected signal to the actual shipboard time when the signal was heard. In so doing, providing they factored in the speed of propagation of sound, they would discover their longitude.
Unfortunately, when the men offered their brainchild to seafarers, they were told that sounds would not carry at sea reliably enough for accurate location finding. The plan might well have died then, had not Whiston hit on the idea of combining sound and light. If the proposed signal guns were loaded with cannon shells that shot more than a mile high into the air, and exploded there, sailors could time the delay between seeing the fireball and hearing its big bang—much the way the weather wise gauge the distance of electrical storms by counting the seconds elapsed between a flash of lightning and a clap of thunder.
Whiston worried, of course, that bright lights might also falter when trying to deliver a time signal at sea. Thus he took special delight in watching the fireworks display commemorating the Thanksgiving Day for the Peace, on July 7, 1713. It convinced him that a well-timed bomb, exploding 6,440 feet in the air, which he figured was the limit of available technology, could certainly be seen from a distance of 100 miles. Thus assured, he worked with Ditton on an article that appeared the following week in The Guardian, laying out the necessary steps.
First a new breed of fleet must be dispatched and anchored at 600-mile intervals in the oceans. Whiston and Ditton didn’t see any problem here, as they misjudged the length requirements for anchor chains. They stated the depth of the North Atlantic as 300 fathoms at its deepest point, when in fact the average depth is more like 2,000 fathoms, and the sea bottom occasionally dips down to more than 3,450.
Where waters were too deep for anchors to hold, the authors said, weights could be dropped through the currents to calmer realms, and would serve to immobilize the ships. In any case, they were confident these minor bugs could be worked out through trial and error.
A meatier matter was the determination of each hull’s position. The time signals must originate from places of known latitude and longitude. Eclipses of the moons of Jupiter could be used for this operation—or even solar or lunar eclipses, since the determinations need not be made with any great frequency. The lunar distance method, too, might serve to locate these hulls, and spare passing ships the difficult astronomical observations and tedious calculations.
All the navigator had to do was watch for the signal flare at local midnight, listen for the cannon’s roar, and sail on, confident of the ship’s position between fixed points at sea. If clouds got in the way, obscuring the flash, then the sound would have to suffice. And besides, another fix on location would come soon from another hull.
The hulls, the authors hoped, would be naturally exempt from all acts of piracy or attack by warring states. Indeed, they should receive legal protection from all trading nations: “And it ought to be a great Crime with every one of them, if any other Ships either injure them, or endeavor to imitate their Explosions, for the Amusement and Deception of any.”
Critics were quick to point out that even if all the obvious obstacles could be overcome, not the least of which was the expense of such an undertaking, many more problems would still stand in the way. A cast of thousands would be required to man the hulls. And these men would be worse off than lighthouse keepers—lonely, at the mercy of the elements, possibly threatened by starvation, and hard pressed to stay sober.
On December 10, 1713, the Whiston-Ditton proposal was published a second time, in The Englishman. In 1714 it came out in book form, under the title A New Method for Discovering the Longitude both at Sea and Land. Despite their scheme’s insurmountable shortcomings, Whiston and Ditton succeeded in pushing the longitude crisis to its resolution. By dint of their dogged determination and desire for public recognition, they united the shipping interests in London. In the spring of 1714, they got up a petition signed by “Captains of Her Majesty’s Ships, Merchants of London, and Commanders of Merchant-Men.” This document, like a gauntlet thrown down on the floor of Parliament, demanded that the government pay attention to the longitude problem—and hasten the day when longitude should cease to be a problem—by offering rich rewards to anyone who could find longitude at sea accurately and practicably.
The merchants and seamen called for a committee to consider the current state of affairs. They requested a fund to support research and development of promising ideas. And they demanded a king’s ransom for the author of the true solution.
6.
The Prize
Her cutty sark, o’ Paisley harn,
That while a lassie she had worn,
In longitude tho’ sorely scanty,
It was her best, and she was vauntine.
—ROBERT BURNS, “Tam o’ Shanter”
The merchants’ and seamen’s petition pressing for action on the matter of longitude arrived at Westminster Palace in May of 1714. In June, a Parliamentary committee assembled to respond to its challenge.
Under orders to act quickly, the committee members sought expert advice from Sir Isaac Newton, by then a grand old man of seventy-two, and his friend Edmond Halley. Halley had gone to the island of St. Helena some years earlier to map the stars of the southern hemisphere—virtually virgin territory on the landscape of the night. Halley’s published catalog of more than three hundred southern stars had won him election to the Royal Society. He had also traveled far and wide to measure magnetic variation, so he was well versed in longitude lore—and personally immersed in the quest.
Newton prepared written remarks for the committee members, which he read aloud to them, and also answered their questions, despite his “mental fatigue” that day. He summarized the existing means for determining longitude, saying that all of them were true in theory but “difficult to execute.” This was of course a gross understatement. Here, for example, is Newton’s description of the timekeeper approach:
“One [method] is by a Watch to keep time exactly. But, by reason of the motion of the Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes, such a watch hath not yet been made.” And not likely to be, either, he implied.
Perhaps Newton mentioned the watch first so as to set it up as a straw man, before proceeding to the somewhat more promising though still problematic field of astronomical solutions. He mentioned the eclipses of Jupiter’s satellites, which worked on land, at any rate, though they left mariners in the lurch. Other astronomical methods, he said, counted on the predicted disappe
arances of known stars behind our own moon, or on the timed observations of lunar and solar eclipses. He also cited the grandiose “lunar distance” plan for divining longitude by measuring the distance between the moon and sun by day, between the moon and stars at night. (Even as Newton spoke, Flamsteed was giving himself a migraine at the Royal Observatory, trying to ascertain stellar positions as the basis for this much-vaunted method.)
The longitude committee incorporated Newton’s testimony in its official report. The document did not favor one approach over another, or even British genius over foreign ingenuity. It simply urged Parliament to welcome potential solutions from any field of science or art, put forth by individuals or groups of any nationality, and to reward success handsomely.
The actual Longitude Act, issued in the reign of Queen Anne on July 8, 1714, did all these things. On the subject of prize money, it named first-, second-, and third-prize amounts, as follows:
£20,000 (the equivalent of millions of dollars today) for a method to determine longitude to an accuracy of half a degree of a great circle;
£15,000 for a method accurate to within two-thirds of a degree;
£10,000 for a method accurate to within one degree.
Since one degree of longitude spans sixty nautical miles (the equivalent of sixty-eight geographical miles) over the surface of the globe at the Equator, even a fraction of a degree translates into a large distance—and consequently a great margin of error when trying to determine the whereabouts of a ship vis-à-vis its destination. The fact that the government was willing to award such huge sums for “Practicable and Useful” methods that could miss the mark by many miles eloquently expresses the nation’s desperation over navigation’s sorry state.
The Longitude Act established a blue ribbon panel of judges that became known as the Board of Longitude. This board, which consisted of scientists, naval officers, and government officials, exercised discretion over the distribution of the prize money. The astronomer royal served as an ex-officio member, as did the president of the Royal Society, the first lord of the Admiralty, the speaker of the House of Commons, the first commissioner of the Navy, and the Savilian, Lucasian, and Plumian professors of mathematics at Oxford and Cambridge Universities. (Newton, a Cambridge man, had held the Lucasian professorship for thirty years; in 1714 he was president of the Royal Society.)
The board, according to the Longitude Act, could give incentive awards to help impoverished inventors bring promising ideas to fruition. This power over purse strings made the Board of Longitude perhaps the world’s first official research-and-development agency. (Though none could have foreseen it at the outset, the Board of Longitude was to remain in existence for more than one hundred years. By the time it finally disbanded in 1828, it had disbursed funds in excess of £100,000.)
In order for the commissioners of longitude to judge the actual accuracy of any proposal, the technique had to be tested on one of Her Majesty’s ships, as it sailed “over the ocean, from Great Britain to any such Port in the West Indies as those Commissioners Choose . . . without losing their Longitude beyond the limits before mentioned.”
So-called solutions to the longitude problem had been a dime a dozen even before the act went into effect. After 1714, with their potential value exponentially raised, such schemes proliferated. In time, the board was literally besieged by any number of conniving and well-meaning persons who had heard word of the prize and wanted to win it. Some of these hopeful contenders were so galvanized by greed that they never stopped to consider the conditions of the contest. Thus the board received ideas for improving ships’ rudders, for purifying drinking water at sea, and for perfecting special sails to be used in storms. Over the course of its long history, the board received all too many blueprints for perpetual motion machines and proposals that purported to square the circle or make sense of the value of pi.
In the wake of the Longitude Act, the concept of “discovering the longitude” became a synonym for attempting the impossible. Longitude came up so commonly as a topic of conversation—and the butt of jokes—that it rooted itself in the literature of the age. In Gulliver’s Travels, for example, the good Captain Lemuel Gulliver, when asked to imagine himself as an immortal Struldbrugg, anticipates the enjoyment of witnessing the return of various comets, the lessening of mighty rivers into shallow brooks, and “the discovery of the longitude, the perpetual motion, the universal medicine, and many other great inventions brought to the utmost perfection.”
Part of the sport of tackling the longitude problem entailed ridiculing others in the competition. A pamphleteer who signed himself “R.B.” said of Mr. Whiston, the fireball proponent, “[I]f he has any such Thing as Brains, they are really crackt.”
Surely one of the most astute, succinct dismissals of fellow hopefuls came from the pen of Jeremy Thacker of Beverly, England. Having heard the half-baked bids to find longitude in the sound of cannon blasts, in compass needles heated by fire, in the moon’s motion, in the sun’s elevation, and what-else-have-you, Thacker developed a new clock ensconced in a vacuum chamber and declared it the best method of all: “In a word, I am satisfied that my Reader begins to think that the Phonometers, Pyrometers, Selenometers, Heliometers, and all the Meters are not worthy to be compared with my Chronometer.”
Thacker’s witty neologism is apparently the first coinage of the word chronometer. What he said in 1714, perhaps in jest, later gained acceptance as the perfect moniker for the marine timekeeper. We still call such a device a chronometer today. Thacker’s chronometer, however, was not quite as good as its name. To its credit, the clock boasted two important new advances. One was its glass house—the vacuum chamber that shielded the chronometer from troubling changes of atmospheric pressure and humidity. The other was a set of cleverly paired winding rods, configured so as to keep the machine going while being wound up. Until Thacker’s introduction of this “maintaining power,” spring-driven watches had simply stopped and lost track of time during winding. Thacker had also taken the precaution of suspending the whole machine in gimbals, like a ship’s compass, to keep it from thumping about on a storm-tossed deck.
What Thacker’s watch could not do was adjust to changes in temperature. Although the vacuum chamber provided some insulation against the effects of heat and cold, it fell short of perfection, and Thacker knew it.
Room temperature exerted a powerful influence on the going rate of any timekeeper. Metal pendulum rods expanded with heat, contracted when cooled, and beat out seconds at different tempos, depending on the temperature. Similarly, balance springs grew soft and weak when heated, stiffer and stronger when cooled. Thacker had considered this problem at great length when testing his chronometer. In fact, the proposal he submitted to the longitude board contained his careful records of the chronometer’s rate at various temperature readings, along with a sliding scale showing the range of error that could be expected at different temperatures. A mariner using the chronometer would simply have to weigh the time shown on the clock’s dial against the height of the mercury in the thermometer tube, and make the necessary calculations. This is where the plan falls apart: Someone would have to keep constant watch over the chronometer, noting all changes in ambient temperature and figuring them into the longitude reading. Then, too, even under ideal circumstances, Thacker owned that his chronometer occasionally erred by as many as six seconds a day.
Six seconds sound like nothing compared to the fifteen minutes routinely lost by earlier clocks. Why split hairs?
Because of the consequences—and the money— involved.
To prove worthy of the £20,000 prize, a clock had to find longitude within half a degree. This meant that it could not lose or gain more than three seconds in twenty-four hours. Arithmetic makes the point: Half a degree of longitude equals two minutes of time—the maximum allowable mistake over the course of a six-week voyage from England to the Caribbean. An error of only three seconds a day, compounded every day at sea for forty days, adds up to
two minutes by journey’s end.
Thacker’s pamphlet, the best of the lot reviewed by members of the Board of Longitude during their first year, didn’t raise anyone’s hopes very high. So much remained to be done. And so little had actually been accomplished.
Newton grew impatient. It was clear to him now that any hope of settling the longitude matter lay in the stars. The lunar distance method that had been proposed several times over preceding centuries gained credence and adherents as the science of astronomy improved. Thanks to Newton’s own efforts in formulating the Universal Law of Gravitation, the moon’s motion was better understood and to some extent predictable. Yet the world was still waiting on Flamsteed to finish surveying the stars.
Flamsteed, meticulous to a fault, had spent forty years mapping the heavens—and had still not released his data. He kept it all under seal at Greenwich. Newton and Halley managed to get hold of most of Flamsteed’s records from the Royal Observatory, and published their own pirated edition of his star catalog in 1712. Flamsteed retaliated by collecting three hundred of the four hundred printed copies, and burning them.
“I committed them to the fire about a fortnight ago,” Flamsteed wrote to his former observing assistant Abraham Sharp. “If Sir I. N. would be sensible of it, I have done both him and Dr. Halley a very great kindness.” In other words, the published positions, insufficiently verified as they were, could only discredit a respectable astronomer’s reputation.
Despite the flap over the premature star catalog, Newton continued to believe that the regular motions of the clockwork universe would prevail in guiding ships at sea. A man-made clock would certainly prove a useful accessory to astronomical reckoning but could never stand in its stead. After seven years of service on the Board of Longitude, in 1721, Newton wrote these impressions in a letter to Josiah Burchett, the secretary of the Admiralty:
“A good watch may serve to keep a recconing at Sea for some days and to know the time of a celestial Observ[at]ion: and for this end a good Jewel watch may suffice till a better sort of Watch can be found out. But when the Longitude at sea is once lost, it cannot be found again by any watch.”