The Day the World Discovered the Sun (31 page)

One can find Hornsby's stunning paper today in the
Philosophical Transactions of the Royal Society
for 1771, sandwiched between accounts of “fossil alkaline salts” in Egypt and “basalt hills” in Germany. The many sciences the Royal Society explored—like its continental peers in Paris and St. Petersburg—were all slowly maturing, each with its own moments of clumsy beauty and scholarly derring-do.

But Hornsby's concluding observation, wrapped in the terse understatement that characterizes many of the greatest scientific papers, is almost
like a dispatch from another age. At a time when eighty-four feet—the altitude of the first balloon flight, still a decade away—was a practically unimaginable distance from the ground, astronomy could nevertheless still slip the bonds of earth and measure hundreds of thousands of interplanetary miles with uncanny precision. Courtesy of characters such as Chappe, Hell, Sajnovics, Green, and Cook, inching a plumb line into outer space and discovering the layout of the entire near universe was now a simple commonplace.

“As the relative distances of the planets are well known, their absolute distances and consequently the dimensions of the Solar System will be as follows,” Hornsby wrote. Here is his chart.

All of Hornsby's calculated (absolute) planetary distances are accurate to between 99.2 percent and 99.6 percent of the correct values.

And somewhere, along the dimly demarcated road between Mars and Jupiter or Venus and Earth, one might imagine marker stones commemorating the lives sacrificed along this pathway to the stars. Here too passed frigates and carriages carrying men no greater than their unparalleled times—yet still measuring up to the greatest standards any space-voyaging civilization might hope to lay down.

When he calculated the dimensions of the solar system in 1771, Thomas Hornsby didn't know how close to spot-on he was. Nevertheless, Hornsby still claimed confidence with gusto. “The uncertainty as to the quantity of the sun's [distance],” Hornsby wrote, “deduced from the observations of the transit of Venus in 1761 . . . seems now to be entirely removed.”
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Hornsby was technically right—at least about the transit data he found most trustworthy. Would that the story of the 1769 Venus transit simply ended here.

In fact, nearly 150 other observers also reported Venus transit data to London and Paris in 1769, 1770, and 1771. Some observers, such as Charles Green's brother-in-law William Wales who observed the transit in Hudson's Bay in present-day Canada, also performed superb observations in extremely challenging conditions. Others, however, were more gentleman dabbler than cutting-edge astronomer, adding their less-than-superior data to the swelling pool of Venus transit studies. Modern statistical analysis of the results would weight the amateur results less than those of the top expeditions and scientists. Statistical analysis was not so sophisticated at the time, however. (Hornsby gives a hint of such methods, albeit incompletely applied, when in his solar parallax calculation he averaged Cook and Green's transit times rather than considering them as independent observations.
²
Hornsby probably did so
because Green's papers at the time of his death were in such disarray that Cook reported having to make “alterations” to Green's Venus transit data just to make it self-consistent.
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) Journals and even newspapers of the time in Paris, London, Vienna, Philadelphia, St. Petersburg, and other cities across Europe and the New World published an estimated six hundred separate calculations based on different combinations of various transit data.
⁴

Naturally, in the aftermath of the 1769 transit, the answer to the question, How far is the sun? depended on whom one asked. The French astronomer, Alexandre Guy Pingré, for instance, calculated a solar parallax of 8.88 arc seconds—99.0 percent of the correct value. Other prominent Swedish and Russian scientists calculated 8.43 and 8.63 arc seconds (95.8 percent and 98.1 percent accurate).
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Before long, delicate egos also entered into the calculations. Father Hell knew that his data from Vardø constituted the most reliable arctic Venus transit observations of any in the world. However, Hell had also withheld his results—indeed any formal announcement about the voyage itself—until he and Sajnovics could prepare a full report for the king of Denmark in February 1770. The
de facto
chairman of the world-wide 1769 Venus transit effort, Jérôme Lalande in Paris, on the other hand, may not have even
known
about Hell and Sajnovics's voyage before Hell's Feb. 1770 publication. In any event, Lalande had also grown all too accustomed to refining his calculations of the solar parallax without any access to the Vardø data. So when Hell's numbers finally arrived in Paris, Lalande viewed them with more suspicion than may have been warranted.
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It didn't help that both Lalande and Hell were prickly personalities whose sensibilities evidently bruised easily. Lalande wrote a lengthy review of Hell's data in the leading French scholarly journal of the time,
Journal des Sçavans.
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Lalande praised some of Hell's astronomical methods but harshly attacked others. Lalande found it laughable, for instance,
that Hell didn't pay proper attention to the atmospheric density in the high arctic and—in Lalande's opinion—damaged his data as a result.

Nevertheless, once armed with Hell and Chappe's data, Lalande calculated a solar parallax very close to Hell's calculated parallax. Lalande found between 8.75 and 8.80 arc seconds. Hell found 8.70 arc seconds. All three solar parallaxes fall close to or within Edmund Halley's 99.2 percent projected accuracy of the Venus transit calculations. Again, posterity pleads the actors in the present melodrama to leave well enough alone.

They did not. Hell wrote a personal letter to Lalande imploring the Frenchman to exclude other arctic Venus transit measurements and use Hell's results instead. Naturally, Lalande took offense at Hell's overreach. But Lalande went too far in his response, turning around and publicly rejecting Hell's data entirely. In an April 1772 monograph, Lalande said a competing Swedish arctic Venus transit observation “has become the most important in all of Europe, serving as a comparison for all remote observations—with which it agrees completely.” As if to poison the porridge for everyone, Lalande then arrived at a new solar parallax value of 8.5 arc seconds (reducing his accuracy of the solar parallax to 96.7 percent).

Lalande's ink-stained fit sent Hell into a fury, causing the snubbed Hungarian
pater
to launch a blistering attack at Lalande in a 116-page memoir of the entire Vardø transit observation. Rightly but for the wrong reasons, Hell urged scientists to ignore Lalande's fusillade and adopt a more reasonable solar parallax value of 8.70 arc seconds—based only on his data and the observations from Cook's voyage.
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“Tahiti and Vardø will be the two columns upon which the true solar parallax of 8.70 [arc seconds] will rest firmly and be preserved,” Hell wrote.
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Lalande and Hell's titanic clashes were only the most conspicuous example of the unintended, but inevitable, result of undertaking such a
vast international science project with so many diverse collaborators. Different teams naturally had different opinions about every aspect of the international effort. And sorting it all out meant political as well as scientific gamesmanship. But no one had come up with a better political solution beyond the prevailing state political model of the day: absolute monarchy. Jérôme Lalande was, in effect, the king of Venus transits. And authority flowed down from him.

So Lalande's sniffy decision to declare the solar parallax 8.5 arc seconds carried more weight than it should have.

Some scientists dared venture their own estimates as low as 8.43 and as high as 8.80 arc seconds.
¹⁰
But it's no great surprise that as late as 1814, a popular account of the 1769 Venus transit voyages stated plainly that “some of the ablest astronomers in Europe . . . [determined] that the horizontal parallax of the sun is, at a mean, about 8 seconds and a half, and his distance from the earth, in round numbers, 95 millions of miles.”

The American lecturer who made this statement, a popular Boston preacher named John Lathorp, sought to translate the heady transit data into an analogy comprehensible to his early-nineteenth-century audience. Lathorp said 95 million miles is a distance “so prodigious that a cannon ball going at the rate of 8 miles in a minute would be more than 22 years in traveling from our globe to the central and solar luminary of its orbit.”
¹¹

The Venus transit voyages of 1761 and 1769 represent mankind's first international “big science” project—a familiar notion in an age of human genome projects, the Hubble space telescope, and the Large Hadron Collider. The transit projects' closest latter-day cousin, though, was another set of voyages that married advanced science and technology with extreme adventure: NASA's Apollo program to land men on the moon the 1960s and 1970s.

Some in the Apollo project considered themselves kindred spirits with explorer-scientists like Captain Cook. In fact the Apollo 15 mission—one with a strong scientific focus—so identified with Venus transit voyagers that the command module was named Endeavour and the astronauts actually brought with them into space a block of wood from the sternpost of the original HMS
Endeavour.
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Equally significant, though, is the analogy between the mission and its consequences for technology and society. The worldwide race to build ever faster computers was already under way when President John F. Kennedy effectively launched the Apollo program on May 25, 1961. But Apollo would give the computer industry one of its most important early economic and technological boosts.

The integrated circuit, and with it industry titans like Intel, came of age when NASA provided vast pools of money and incentive to build the smallest, fastest, and lightest computer components imaginable.
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It is no small coincidence that the same country that won the race to land men on the moon has in the decades since fostered a national industry—from UNIVAC and IBM to Apple, Microsoft, Google, and beyond—that remains the world's greatest designer, builder, and developer of computers and computer software.

So too with the Venus transit voyages of the 1760s and the military and geopolitical problem of finding navigation at sea. The technical battles pitting lunars against the nautical chronometer would have happened regardless of Venus's motions in the sky. But once the 1761 and 1769 transit voyages had overtaken the European imagination, summoning with it considerable royally sanctioned piles of money, projects like Nevil Maskelyne's world-changing
Nautical Almanac
became not only feasible but inevitable.

Although recent books and television coverage of the longitude race have put clockmaker John Harrison's genius rightfully in the spotlight, the pendulum of history now must swing back toward a slightly more
complex reality. Harrison's chronometers will forever constitute an important piece of the longitude puzzle, especially in the nineteenth century, when the chronometers' greatest innovations could be cheaply and reliably mass manufactured. But from the 1760s through at least the 1820s, the lunar longitude methods that Maskelyne and his fellow Venus transit pioneers mastered remained a staple of British sea power and her vast and rapidly growing global empire—even assisting her former colonial possessions.

In 1822, for instance, a navigational handbook,
The American Practical Lunarian and Seaman's Guide
, quoted Pastor Lathorp's above enthusiastic description of the 1769 Venus transit—cannonball analogy and all. The
Guide
informed its readership that, more than two generations after Harrison had won the Longitude Prize, the pragmatic reality of navigation at sea still belonged to Maskelyne. “Every commander navigating a vessel to foreign ports should furnish himself with a good brass sextant, a
Nautical Almanac
and the requisite tables given in the epitomes of navigation,” the
Guide
stated. “These are all that are required for the purpose of finding longitude.”
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As reliable as Newton's laws, the law of unintended consequences holds true for the Venus transit voyages too.

Charles Mason and Jeremiah Dixon, first paired together to observe the 1761 Venus transit, had executed their job with such skill under such trying circumstances that the Royal Society employed the astronomers during the years 1763 through 1767 surveying disputed borders between the colonies of Maryland, Pennsylvania, Delaware, and Virginia. Neither Venus transit voyager would live to see the abbreviation of one of their names—Dixie—that would become synonymous with an entire region of America and, ultimately, emblematize the civil war of which Mason and Dixon's line marked the epicenter.

Captain Cook's Venus transit voyage had returned to such fanfare and acclaim that the British Admiralty soon commissioned a second
(1772–1775) and later third voyage (1776–1779) to follow swiftly on the heels of one another. Cook's three voyages, the last of which ended with his death in a battle on the beaches of Hawaii, changed the world like precious few nautical adventures since the days of Columbus. In addition to effectively opening the Pacific for broad and extended explorations, Cook had so mastered the battle against scurvy that it would never again pose an insurmountable problem for globe-spanning mariners.
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