The Planets (8 page)

In the heat of this age of exploration, in 1543, a Polish cleric publishes a book that moves the entire world to a new locale.
De Revolutionibus,
by Nicolaus Copernicus, plucks the earth from its stationary post at the hub of the celestial spheres, and sets it spinning around the Sun, between the orbits of Venus and Mars. The strangeness and unpopularity of Copernicus’s opinion nearly silence it, but within one hundred years, against all expectation, the Sun takes over the center of the universe, and our world voyages as a wandering star.

Doesn’t this new planet deserve a name? If Champlain can christen his lake and Hudson his bay, why must the newly mobile globe labor under an old, inaccurate term? “Earth” recalls the ancient division of all ordinary matter into four elements—earth, water, air, fire—and the designation of earth as the heaviest, least heavenly among them. In that scheme, water flowed over earth, air floated above both, and fire rose through air to the threshold of the celestial spheres, where planets and stars embodied a fifth element—quintessence. With world order shifting on maps of the heavens, might not “the earth” take a proper name from mythology? But already it is too late to dislodge the old name, too late even to change it from “earth” to “water,” now that seas can be seen to yawn and stretch in all directions.

Mapmakers decorate the blank expanses of ocean with ships, with whales and sea monsters, with puff-cheeked cherubs exhaling gales, and also with map titles and legends framed in elaborate cartouches as large as some countries.

At least one compass rose, a flower-like emblem often rendered in gold leaf, indigo, and cochineal, now orients each map, with thirty-two painted petals pointing in every possible direction of wind and headway. The rose realizes all the logbook shorthand of exploration’s zigzag course—ENE, SSW, NW by N—and mirrors the face of the magnetic compass that dictates those notations.

The magnetic compass, indispensable to mariners since at least the thirteenth century, helps them find the North Star even when clouds obscure it—even when their ship has sailed so far south as to plunge that guiding light below the horizon. Many think the compass needle must be attracted to the Pole Star, if not to some invisible celestial point close by it.

But no, the earth itself is the magnet that draws all compass needles to its iron heart. William Gilbert, an English doctor, discovers this truth through experimentation in 1600, and demonstrates the effect for Queen Elizabeth by using a small spherical magnet to model the earth. Furthermore, Gilbert scorns the universal prohibition against garlic on shipboard, by showing that neither garlic fumes nor garlic smeared on a compass needle can diminish its magnetic power.

The magnetic nature of the earth leads Gilbert and others to suspect magnetism as the force that keeps the planets in their orbits. Newton’s universal gravity trumps Gilbert’s interplanetary magnetism in 1687, but still the magnetic earth holds promise for navigation. Although compass needles generally tend north, a magnetic compass points slightly east of north in one part of the world, and slightly west of north in another. Columbus had noticed this shift on his outward voyage, and feared his instrument was failing him. By the seventeenth century, however, cumulative experience suggests the phenomenon may be exploitable. Perhaps the degree of “variation” of the compass can be measured from place to place, and the featureless oceans resolved into magnetic zones to help sailors establish their whereabouts during weeks or months at sea. This possibility launches the first purely scientific voyage, under the command of Edmond Halley, the only Astronomer Royal ever to win a commission as captain in the Royal Navy.

Between 1698 and 1700, Halley leads two expeditions across the Atlantic Ocean, and also to the Atlantic’s northern and southern limits until stopped by icebergs in fog. Off the coast of Africa
and again near Newfoundland, Halley’s specially designed flat-bottomed vessel, the
Paramore,
draws friendly fire from English merchantmen and colonial fishermen who mistake her for a pirate ship.

The map Halley publishes in color in 1701 fills the ocean with curving lines of varying lengths and widths describing degrees of magnetic variation east and west. The continents bordering the Atlantic serve merely to anchor the all-important lines, and to bear the cartouches, whose palm trees, muses, and naked natives have been bumped from the busy waters to the empty lands.

Halley concludes with honesty that magnetic variation will be of no real use to sailors as a means of determining longitude. What’s more, he predicts his carefully drawn lines will shift over time as a result of motions deep within the earth. Halley (presciently) envisions the interior of the planet in alternating shells of solid and molten material that control its magnetic behavior.

Meanwhile Halley’s map of magnetic variation, though a disappointment to him and to his fellow seamen, foments a revolution in cartography. Its curved lines connecting points of equal values (to be hailed as Halleyan lines for a hundred years) add a third dimension to printed maps. Other maps
of Halley’s—of the stars of the southern hemisphere, the Trade Winds, the predicted path of the 1715 solar eclipse—also gain notoriety for their innovations. For his part, he would chart the whole Solar System if only he could gauge the mileage from the earth to the Sun.
*

Halley discerns a way to make this key measurement on the special occasion of a transit of Venus: By watching and timing the event from widely separated points on the globe, scientists could triangulate the sky to calculate the distance from the earth to Venus, then deduce the earth’s distance from the Sun. Halley predicts two transits, for 1761 and 1769, but he will have to live to the age of 105 to see even the first of the pair. For although Venus passes between the Sun and the earth five times every eight years, her tilted orbit usually carries her above or below the Sun, from our perspective. In order for Venus to be seen crossing the Sun’s face, she must intersect the plane of the earth’s orbit—within two days of the earth’s intersecting Venus’s orbital plane. These stringent requirements permit two transits to follow within
eight years of one another, but only a single such pair per century.

“I strongly urge diligent searchers of the heavens (for whom, when I shall have ended my days, these sights are being kept in store) to bear in mind this injunction of mine,” writes Halley in 1716 of the coming Venus transits, “and to apply themselves actively and with all their might to making the necessary observations.”

When the time of the first transit comes, in June of 1761, Halley’s followers face all manner of disasters—hostile armies, monsoons, dysentery, floods, severe cold—to cover prime observing sites in Africa, India, Russia, and Canada, as well as several European cities. Clouds foil most of the expeditions, however, and astronomers’ indeterminate results focus even greater attention on the next opportunity, in 1769, which dispatches 151 official observers to 77 locations around the world.

Each group must time the four crucial moments of the transit, called “contacts,” when Venus and the Sun touch rim to rim. The first occurs as Venus appears to attach herself to the outside of the Sun’s circle. Second contact soon follows, as Venus enters fully inside the Sun’s embrace, but it takes hours for her to achieve third contact on the
far side of the solar disk. By fourth contact she has already exited the Sun, and stands on the brink of separation.

Responsibility for the Royal Society’s all-important observations at King George III Island (Tahiti) falls to Lieutenant James Cook. He sets out from England the year before, in August of 1768, so as to arrive in time to make preparations that include the building of a secure observatory, Fort Venus.

“Saturday 3
^rd
June [1769]. This day prov’d as favourable to our purpose as we could wish, not a Clowd was to be seen the whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk: we very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the Contacts particularly the two internal ones. D
^r
Solander observed as well as M
^r
Green and my self, and we differ’d from one another in observing the times of the Contacts much more than could be expected. M
^r
Greens Telescope and mine were of the same Mag[n]ifying power but that of the D
^r
was greater then ours.”

Through no one’s fault, astronomers everywhere
encounter the same difficulties as Cook’s men in judging the exact moments of Venus’s entry into and exit from the Sun’s disk. The limitations of even the best available optics undermine everyone’s results, and the international astronomical community must be content with merely narrowing the earth-Sun distance to something between 92 and 96 million miles.

Cook turns his attention from Venus to the second, secret part of his instructions—a sortie through the icy sea in search of the great southern Terra Incognita. Failing to find it on this quest, he returns home, but mounts a second discovery attempt in 1772. Through three cold years of effort Cook, now made Captain, becomes adept at turning his ship frequently into the wind to shake the snow from her sails.

“Monday 6
^th
February [1775]. We continued to steer to the South and SE till noon at which time we were in the Latitude of 58° 15′ S Longitude 21′ 34′ West and seeing neither land nor signs of any, I concluded that what we had seen which I named Sandwich Land was either a group of Isles &c
^a
or else a point of the Continent, for I firmly believe that there is a tract of land near the Pole, which is the source of most of the ice which is spread over
this vast Southern Ocean….I mean a land of some considerable extent….It is however true that the greatest part of this Southern Continent (supposing there is one) must lay within the Polar Circle where the Sea is so pestered with ice that the land is thereby inaccessible.”

Cook’s reckoning of latitude and longitude surpasses the accuracy of all who preceded him in such pursuits. By tracking the motion of the Moon against the stars—a method Halley helped to develop—and with the aid of a new timekeeper that keeps up with the master clock back home at the Greenwich Observatory, Cook knows exactly where he is. His maps show others the way from Success Bay in Tierra del Fuego, his source of wood and water, to Botany Bay in Australia, which he named for its abundance of new plant species, and Poverty Bay, New Zealand, where Cook found “no one thing we wanted.”

Ships laden with surveying instruments—ships that not only cross oceans but can course close to the land all along coastlines and into the mouths of rivers—now start to reexamine the New World with new precision. This is the mission of H.M.S.
Beagle
in 1831, whose captain carries twenty-two of the best available chronometers—timekeepers
of the type Cook praised on his second voyage. Bound for a detailed survey of South America and then home the long way around via the East Indies, Captain Robert FitzRoy seeks a gentleman companion who shares his interests in geology and natural history, and who will pay his own way. Charles Darwin, a twenty-two-year-old recent college graduate unsure of his life’s vocation, signs on.

The
Beagle
tortures Darwin with seasickness. Although he may freely, legally abandon ship at any port, he stays the full tour of duty, which lasts five years. He copes by spending as much time as possible engaged ashore while FitzRoy coasts the whole of Argentina, Chile, and the Falkland and Galápagos Islands to make maps.

“I stayed ten weeks at Maldonado, in which time a nearly perfect collection of the animals, birds, and reptiles, was procured,” Darwin reports of the summer of 1832. “I will give an account of a little excursion I made as far as the river Polanco, which is about 70 miles distant, in a northerly direction. I may mention, as proof of how cheap everything is in this country, that I paid only two dollars a day, or eight shillings, for two men, together with a troop of about a dozen riding-horses. My companions were well armed with pistols and sabres; a precaution
which I thought rather unnecessary; but the first piece of news we heard was, that, the day before, a traveler from Monte Video had been found dead on the road, with his throat cut. This happened close to a cross, the record of a former murder.”

Despite the dangers of the local wars, Darwin still prefers the land to the sea:

“August 11
^th
[1833]—Mr Harris, an Englishman residing at Patagones, a guide, and five Gauchos, who were proceeding to the army on business, were my companions on the journey…. Shortly after passing the first spring we came in sight of a famous tree, which the Indians reverence as the altar of Walleechu…. About two leagues beyond this curious tree we halted for the night: at this instant an unfortunate cow was spied by the lynx-eyed Gauchos. Off they set in chase, and in a few minutes she was dragged in by the lazo, and slaughtered. We here had the four necessaries of life ‘en el campo,’—pasture for the horses, water (only a muddy puddle), meat, and firewood. The Gauchos were in high spirits at finding all these luxuries; and we soon set to work at the poor cow. This was the first night which I had ever passed under the open sky, with the gear of the
recado
[saddle] for my bed.
There is high enjoyment in the independence of the Gaucho life—to be able at any moment to pull up your horse, and say, ‘Here we will pass the night.’ The deathlike stillness of the plain, the dogs keeping watch, the gypsy-group of Gauchos making their beds round the fire, have left in my mind a strongly marked picture of this first night, which will not soon be forgotten.”