Einstein's Clocks and Poincare's Maps

by Peter Galison

  In tiny, far-flung observatories, the American, British, and French sentries of time took their readings from the skies and matched them against the pulses from their cables. Stars told each station its local time, cables whispered to them of time somewhere else. It was devilishly hard work, demanding precision results, strong cables, and orchestrated teamwork. One of de Bernardières’ French collaborators perched his station near the ruins of the city of Chorillos, just south of Lima. Another waited by his telegraph in the observatory of the naval school in Buenos Aires. Linking up the various wires, de Bernadières began signaling electrically from Valparaiso to Panama. All along the route, relay men struggled to keep the signal moving without a break: the tiny current tickling the mirror; reflected light flickering. As soon as he saw the light spot move, the operator would relaunch the signal. Starting on 18 January 1883, while the Americans were still readying crates in Washington for their expedition along the coast of Peru and Argentina, the French team seized three excellent astronomical and electrical evenings. Just after their last measurement, the submarine cable into Panama snapped, severing communication between their minuscule observatory and Paris. But they had results: the longitude of the flagpole over the stock market of Valparaiso stood 4 hours, 55 minutes, and 54.11 seconds earlier than the Montsouris time room thousands of miles to the east.

  It was just after this intense round of competition and collaboration with the Americans that, on 7 April 1884, de Bernardières issued his plea to his academician colleagues in Paris. His report told the scientists that there were new possibilities for French surveying: two great oceans had just been linked across South America by telegraph, with cables snaking their way at 12,000 feet across the formidable Andes. As de Bernardières put it, the Paris Bureau of Longitude should now imagine creating an “immense geodesic network that would encompass the entire globe, fixing precisely its form and dimensions.”90

  The French Navy backed the plan, lending officers, sailors, and matériel. De Bernardières would install himself at Santiago or nearby Valparaiso, and others would tell time to the north in Lima and Panama and across the continent in Buenos Aires. Just a few months earlier, the American company Central and South American Cable had laid their undersea line from Lima to Panama. Adding to an already established line stretching from Panama through the Greater Antilles, North America to Europe, de Bernardières and his colleagues had a filamentary link all the way back to Paris. Since other lines also went from Valparaiso through Buenos Aires, the Cape Verde Islands and eventually to Europe, the whole constituted a vast circuit of some 20,000 miles of gutta-percha-covered copper, allowing the two routes to check one another.

  Out of Green’s American mission and de Bernardières’s French one came an enormous, world-clasping polygon of simultaneity with vertices in Paris, Greenwich, Washington, Panama, Valparaiso, Buenos Aires, Rio de Janeiro, and Lisbon. Amazingly enough, reckoned in two different directions, this irregular octogon came within 150 yards of closing. From the polygon, spokes jutted out to Asia where the Americans were electrically grasping the contours of India, while the French, from a fragile bamboo hut, a few pieces of electrical equipment, some astronomical gear, and a cable-end, began their electrical pinpointing of Haiphong.91

  This French world net of cables and time signals shot east, west, north, and south from Paris. Astronomers shaped much of its character, and in turn, the longitude machine transformed their observatories. Take, for example, the fourth volume of the Annales du Bureau des Longitudes, which in 1890 opened with an account of the Bordeaux Observatory. Whatever research might yield, the report made plain, the observatory was built neither to scout new phenomena nor to place the human form in a cosmic context. No, the city of Bordeaux, like so many others, had built an observatory to set ship’s chronometers so they could determine their longitude at sea.92 This meant that the Observatory’s very first task was to establish its own longitude, which it completed by using telegraphic time signals with Paris on 19 November 1881, locating itself 11 minutes and 26.444 seconds west of the capital—plus or minus eight-thousandths of a second.

  Figure 3.10 Cabled Time in South America. One of the major French longitude explorers, de Bernardières raced against the Americans to complete an electric-time-based cartographic net tied back to the Paris Observatory. To his colleagues back at the Academy of Sciences, the Frenchman urged the creation of the polygon sketched here: “an immense geodesic network that would encompass the entire globe.” SOURCE: MAP MODIFIED FROM THE TIMES ATLAS, LONDON, OFFICE OF THE TIMES, 1986.

  City by city, country by country, the French Bureau of Longitude extended its network of longitudinal fixed points, first nationally, running telegraph wires from Paris to the distant cities of France, and then, through an array of undersea cables, to the distant colonies. By 1880, ninety thousand miles of mostly British cable lay on the ocean floor, a ninety-million-pound machine binding every inhabited continent, cutting across to Japan, New Zealand, India, through the West Indies, the East Indies, and the Aegean. Competing for colonies, for news, for shipping, for prestige, inevitably the major powers clashed over telegraphic networks. For through copper circuits flowed time, and through time the partition of the worldmap in an age of empires.

  As maps merged, a consensus emerged that a universally acknowledged first meridian was needed. That origin arc would set one nation’s capital at the symbolic center of every global map. Every clock and every longitude measurement in the world would refer back to the dead center of one country’s transit instrument. Though the immediate struggle was over a symbolic centrality rather than control of land, no one mistook its importance. High noon for the diplomats and scientists was to be 1 October 1884 in Washington, D.C., in the Diplomatic Hall of the American State Department.

  Battle over Neutrality

  Two years prior to the meeting, in August 1882, President Chester A. Arthur and the American Congress had approved a resolution calling for an international conference to be assembled in Washington for the purpose of setting a unique and universal prime meridian.93 While American politicians came to consensus, a group of scientific delegates gathered for an international geodesic conference convened in Rome in October 1883. Swiss astronomer Adolphe Hirsch reported on their deliberations, starting with their celebration of the network of telegraphic longitude fixes that had finally specified reference points across the European continent. With many countries producing maps with their own capitals as the zero longitude point, a new question had arisen: Could all these reference points be referred back to one single and unique prime meridian line? Now, Hirsch recorded, it was time to set aside ideals of a science isolated from the world and instead to make a contribution that, in a far deeper way, joined science and the wider practical domain. Great nations had an opportunity to help navigation, cartography, geography, meteorology, rail transport, and telegraphic communication. It was time, once and for all, to choose a universal prime meridian. Just because the earth was a sphere, Hirsch insisted, there was no natural prime meridian. That is, a prime latitude—the equator—was picked out naturally by the spin of the earth. But “nature” had selected no prime meridian of longitude. Even the magnetic north pole could not be used to single out any particular longitude as prime, as the magnetic north wandered about over time. No, the choice of a prime meridian was necessarily arbitrary and therefore subject to reasons “purely practical and conventional [conventionelle].”

  Here was a theme the experts repeated over and over again: the exchange of ideas, products, and peoples demanded new international institutions even while respecting the individuality of nations. Global conventions must prevail over local ones. Unions of post and telegraphs now embraced the entire world. The Convention of the Meter already united the majority of civilized countries, there were conventions of electrical standards; conventions to protect intellectual, artistic, and industrial property; conventions to protect combatants in conflict. Even their own geodesic association testified that a p
urely scientific goal—the establishment of the exact shape of the earth—could propel such coordination among nations. Hirsch insisted that it was time to find a practical solution to the unification of longitude, and the conference therefore recommended that Greenwich become that prime meridian, with a date change at the antimeridian on the opposite side of the earth.94

  A year after Rome, the delegates to the Washington Conference joined U.S. Secretary of State Frederick T. Frelinghuysen at the State Department. With a rigorous record of the conference prepared and approved as it progressed, the statesmen and scientists joined the battle over the longitudinal zero point. Poincaré of course read these proceedings; he even cited them verbatim in his later articles. He, along with many others who studied the proceedings, witnessed the inextricable mix of politics, philosophy, astronomy, and surveying.

  After a formal welcome by the secretary of state in which he pointedly renounced establishing the prime meridian in the United States, Lewis M. Rutherfurd of the American delegation shot the starting gun by proposing, as had the Rome Conference, that the standard meridian pass through the center of the transit instrument at Greenwich Observatory. French Minister Plenipotentiary and Consul-General to Canada Albert Lefaivre immediately cautioned against hasty action, belittling the Rome decisions as the product of mere “experts.” Here in Washington, the loftier vantage point of politicians ought to prevail: “It is, moreover, our privilege to be philosophers and cosmopolitans, and to contemplate the interests of mankind not only for the present, but for the most distant future.”95 Only such a distanced view would allow consideration of principles. Backing down, the Americans proposed that the conference merely accept the idea of a single prime meridian.

  Such backtracking offended the British. Captain Sir F.J.O. Evans of the Royal Navy protested that Rome had already narrowed the question: the prime meridian should bisect a great observatory, not a mountain, a strait, or a monumental building. Science, after all, demands precision, not some vague gesture toward a natural feature of the earth. And the list of such great observatories was short: Paris, Berlin, Greenwich, and Washington.96 Commander Sampson of the United States Navy concurred, saying that the chosen observatory must have the requisite telegraphic time links to the whole world: “We may then say that, from a purely scientific point of view, any meridian may be taken as the prime meridian.” If one demanded convenience and economy there were fewer options, and that choice narrowed considerably if the prime meridian had to pass through a thoroughly wired, governmentally backed observatory. If one recognized that any prime meridian other than the British one would require altering maps for the 70 percent of world shipping that used the Greenwich meridian, there was only one real choice: Greenwich.97 No doubt encouraged by the twin salvoes of the British and American navies, Rutherfurd rejoined the siege of Paris: “The observatory of Paris stands within the heart of a large and populous city,” a city subject to movement of air, tremors of the earth. The Paris Observatory had to be moved. “The only thing which keeps it there is the remembrance of the honorable career of that observatory in times past.”98

  Not so, the French astronomer and delegate Jules Janssen retorted. The Paris Observatory remained vital because it was linked electrically with all the other major observatories, its abilities well documented by a use of telegraphic mapping altogether comparable to Greenwich. What mattered historically was this: Following Ptolemy, Cardinal Richelieu had set the prime meridian on the island of Ferro in the Canary Islands. Since the easternmost point of Ferro rose from the sea some 19°55'3" degrees west of Paris, reckonings became hard to calculate. Eighteenth-century French astronomers simplified longitude calculations by decreeing that Ferro’s prime meridian would be, statutorily, exactly 20 degrees west of Paris. Since even French astronomers could not physically move the island of Ferro 4'57" east, Janssen admitted that this convention made the prime meridian Paris, disguised.

  No doubt Janssen could read the politics as well as anyone else: the likelihood of replacing Greenwich by Paris (disguised as Ferro) as the prime meridian was nil. But Janssen was not about to fold his tent. (This was an astronomer who, during the siege of Paris in 1870, had taken off in violent winds in a balloon for Algeria to observe an eclipse.) It was time to seize loftier ground than Ptolemaic (and now French) Ferro, for the conference was beginning to skid toward the crassest of decisions. “Instead of laying down the great principle that the meridian to be offered to the world as the starting-point for all terrestrial longitudes should have, above all things, an essentially geographical and impersonal character, the question was simply asked, which one of the meridians in use among the different observatories has (if I may be allowed to use the expression) the largest number of clients?”99

  Clients. The very thought offended a rational (French) sensibility. Janssen hoped that customs and customers would not throw industrial (British) smoke before philosophical (French) principles. There was, he reminded the assembled, the long tradition of French hydrographic engineers; there was the universally respected almanac, the Connaissance des Temps. And not least his colleagues ought to remember that it was the French who, in revolutionary times, had stepped past the pied de Roi as a unit of length in favor of the rational meter. Rational science should trump royal trade.100 Janssen opined: “Without doubt, on account of our long and glorious past, of our great publications, of our important hydrographic works, a change of meridian would cause us heavy sacrifices. Nevertheless, if we are approached with offers of self-sacrifice, and thus receive proofs of a sincere desire for the general good, France has given sufficient proofs of her love of progress to make her cooperation certain.” A reasonable agreement, Janssen concluded, cannot protect only one contracting party.101 In other words, put the longitudinal center of the world anyplace neutral. Anyplace but Greenwich.

  Come, come, the British astronomer John Couch Adams harrumphed. It was Adams whose work had already been twice mobilized in skirmishes with the French, once over the question of who had discovered Neptune and again when he contradicted the results of the great Laplace on the motion of the moon. We are not belligerents, he now insisted, we are all neutral, as in all matters scientific. We are not dividing territory as after a war but in a friendly way representing friendly nations. What will provide the greatest convenience to the world? And we should provide that convenience without the legal fictions of a displacement from some other observatory (Paris disguised as Ferro), but rather calling things “by their right names.” Practical, hard-headed decision making ought to be the order of the day: “It was quite clear that if all the Delegates here present were guided by merely sentimental considerations, or by considerations of amour propre, the Conference would never arrive at any conclusion.” To the charge of French vanity, Janssen answered by accusing the British of vulgar self-indulgence:

  We consider that a reform which consists in giving to a geographical question one of the worst solutions possible, simply on the ground of practical convenience, that is to say, the advantage to yourselves and those you represent, of having nothing to change, either in your maps, customs, or traditions—such a solution, I say, can have no future before it, and we refuse to take part in it.102

  Loyal to the practical and commercial, the Americans sided with the British. What is neutral? demanded Cleveland Abbe. Historical, geographical, scientific, or arithmetical neutrality? True, France gave us neutral weights and measures, but those measures have an arbitrariness to them by virtue of the standard weights and measures on which they rest. “Neutral” system of longitude is “a myth, a fancy, a piece of poetry,” unless you can tell precisely how to do it.103

  Janssen retorted: A neutral point would have two advantages, geographical and moral. Choosing the Bering Strait would remove the prime meridian from all centers of population for the statutory change of date, it would neatly slice the globe into the Old World and the New. Or, if not the Bering Strait, then another remarkable physical point; laying the zero point of time and
longitude through the Azores would cost less than the Bering Strait because telegraphic cables already ran near. In either the Azores or the Bering Strait, one would define the zero of longitude from existing telegraph-connected observatories, not the center of the strait itself. (Janssen had just noted the excellent electrical connectivity of the Paris Observatory.) No doubt looking pointedly to Adams, Janssen urged his colleagues to bear in mind the “lively discussion” raised by the English and French press over the discovery of Neptune (both sides had claimed astronomical priority). Delving deeper into the past, Janssen saw those same Continental-British tensions in seventeenth-century battles over the calculus between defenders of Newton and those of Leibniz: “The love of glory is one of the noblest motives of men; we must bow before it, but we must also be careful not to permit it to produce bad fruits.”104

  Outnumbered, Janssen soldiered on: economic reasons might favor Greenwich, Washington, Paris, Berlin, Pulkovo, Vienna, or Rome, but such choices would necessarily be artificial. “Whatever we may do, the common prime meridian will always be a crown to which there will be a hundred pretenders. Let us place the crown on the brow of science, and all will bow before it.” Yes, one Anglo-Saxon responded, but any chosen place belongs to a country. Not at all, shot back Janssen; the equator is neutral, yet it traverses nations. England’s General Strachey protested against the distinction between longitude for geography and for astronomy—“longitude is longitude.” It most certainly is not, Janssen seethed. Longitude depends like any measure on context. “Is not a weighing necessary to determine a chemical equivalent of an entirely different kind from that of a commercial weighing? Yet it is still a weight.”105