Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time - Dava Sobel (2005)
Chapter 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 times; 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.
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.