on a Wednesday excursion when I was a little girl, my father
bought me a beaded wire ball that I loved. At a touch, I could
collapse the toy into a flat coil between my palms, or pop
it open to make a hollow sphere. Rounded out, it resembled
a tiny Earth, because its hinged wires traced the same pattern
of intersecting circles that I had seen on the globe in my
schoolroom-the thin black lines of latitude and longitude.
The few colored beads slid along the wire paths haphazardly,
like ships on the high seas.
My father strode up Fifth Avenue
to Rockefeller Center with me on his shoulders, and we stopped
to stare at the statue of Atlas, carrying Heaven and Earth
on his. The brone orb that Atlas held aloft, like the wire
toy in my hands, was a see-through world, defined by imaginary
lines. The Equator. The Ecliptic. The Tropic of Cancer. The
Tropic of Capricorn. The Arctic Circle. The prime meridian.
Even then I could recognize, in the graph-paper grid imposed
on the globe, a powerful symbol of all the real lands and
waters on the planet.
Today, the latitude and longitude
lines govern with more authority than I could have imagined
forty-odd years ago, for they stay fixed as the world changes
its configuration underneath them with continents adrift across
a widening sea, and national boundaries repeatedly redrawn
by war or peace.
As a child, I learned the trick
for remembering the difference between latitude and longitude.
The latitude lines, the parallels, really do stay parallel
to each other as they girdle the globe from the Equator to
the poles in a series of shrinking concentric rings. The meridians
of longitude go the other way: They loop from the North Pole
to the South and back again in great circles of the same size,
so they all converge at the ends of the Earth.
Lines of latitude and longitude
began crisscrossing our worldview in ancient times, at least
three centuries before the birth of Christ. By A.D. 150, the
cartographer and astronomer Ptolemy had plotted them on the
twenty-seven maps of his first world atlas. Also for this
landmark volume, Ptolemy listed all the place names in an
index, in alphabetical order, with the latitude and longitude
of each- as well as he could gauge them from travelers' reports.
Ptolemy himself had only an armchair appreciation of the wider
world. A common misconception of his day held that anyone
living below the Equator would melt into deformity from the
The Equator marked the zero-degree
parallel of latitude for Ptolemy. He did not choose it arbitrarily
but took it on higher authority from his predecessors, who
had derived it from nature while observing the motions of
the heavenly bodies. The sun, moon, and planets pass almost
directly overhead at the Equator. Likewise the Tropic of Cancer
and the Tropic of Capricorn, two other famous parallels, assume
their positions at the sun's command. They mark the northern
and southern boundaries of the sun's apparent motion over
the course of the year.
Ptolemy was free, however, to
lay his prime meridian, the zero-degree longitude line, wherever
he liked. He chose to run it through the Fortunate Islands
(now called the Canary & Madeira Islands) off the northwest
coast of Africa. Later mapmakers moved the prime meridian
to the Azores and to the Cape Verde Islands, as well as to
Rome, Copenhagen, Jerusalem, St. Petersburg, Pisa, Paris,
and Philadelphia, among other places, before it settled down
at last in London. As the world turns, any line drawn from
pole to pole may serve as well as any other for a starting
line of reference. The placement of the prime meridian is
a purely political decision.
Here lies the real, hard-core
difference between latitude and longitude beyond the superficial
difference in line direction that any child can see: The zero-degree
parallel of latitude is fixed by the laws of nature, while
the zero-degree meridian of longitude shifts like the sands
of time. This difference makes finding latitude child's play,
and turns the determination of longitude, especially at sea,
into an adult dilemma; one that stumped the wisest minds of
the world for the better part of human history.
Any sailor worth his salt can
gauge his latitude well enough by the length of the day, or
by the height of the sun or known guide stars above the horizon.
Christopher Columbus followed a straight path across the Atlantic
when he "sailed the parallel" on his 1492 journey, and the
technique would doubtless have carried him to the Indies had
not the Americas intervened.
The measurement of longitude meridians,
in comparison, is tempered by time. To learn one's longitude
at sea, one needs to know what time it is aboard ship and
also the time at the home port or another place of known longitude
at that very same moment. The two clock times enable the navigator
to convert the hour difference into a geographical separation.
Since the Earth takes twenty-four hours to complete one full
revolution of three hundred sixty degrees, one hour marks
one twenty-fourth of a spin, or fifteen degrees. And so each
hour's time difference between the ship and the starting point
marks a progress of fifteen degrees of longitude to the east
or west. Every day at sea, when the navigator resets his ship's
clock to local noon when the sun reaches its highest point
in the sky, and then consults the home-port clock, every hour's
discrepancy between them translates into another fifteen degrees
Those same fifteen degrees of
longitude also correspond to a distance traveled. At the Equator,
where the girth of the Earth is greatest, fifteen degrees
stretch fully one thousand miles. North or south of that line,
however, the mileage value of each degree decreases. One degree
of longitude equals four minutes of time the world over, but
in terms of distance, one degree shrinks from sixty-eight
miles at the Equator to virtually nothing at the poles.
Precise knowledge of the hour
in two different places at once, a longitude prerequisite
so easily accessible today from any pair of cheap wristwatches,
was utterly unattainable up to and including the era of pendulum
clocks. On the deck of a rolling ship, such clocks would slow
down, or speed up, or stop running altogether. Normal changes
in temperature encountered en route from a cold country of
origin to a tropical trade zone thinned or thickened a clock's
lubricating oil and made its metal parts expand or contract
with equally disastrous results. A rise or fall in barometric
pressure, or the subtle variations in the Earth's gravity
from one latitude to another, could also cause a clock to
gain or lose time.
For lack of a practical method
of determining longitude, every great captain in the Age of
Exploration became lost at sea despite the best available
charts and compasses. From Vasco da Gama to Vasco Nunez de
Balboa, from Ferdinand Magellan to Sir Francis Drake- they
all got where they were going willy-nilly, by forces attributed
to good luck or the grace of God.
As more and more sailing vessels
set out to conquer or explore new territories, to wage war,
or to ferry gold and commodities between foreign lands, the
wealth of nations floated upon the oceans. And still no ship
owned a reliable means for establishing her whereabouts. In
consequence, untold numbers of sailors died when their destinations
suddenly loomed out of the sea and took them by surprise.
In a single such accident, on October 22, 1707, at the Scilly
Isles near the southwestern tip of England, four homebound
British warships ran aground and nearly two thousand men lost
The active quest for a solution
to the problem of longitude persisted over four centuries
and across the whole
continent of Europe. Most crowned heads of state eventually
played a part in the longitude story, notably King George
III of England and King Louis XIV of France. Seafaring men
such as Captain William Bligh of the Bounty and the great
circumnavigator Captain James Cook, who made three long voyages
of exploration and experimentation before his violent death
in Hawaii, took the more promising methods to sea to test
their accuracy and practicability.
Renowned astronomers approached
the longitude challenge by appealing to the clockwork universe:
Galileo Galilei, Jean Dominique Cassini, Christiaan Huygens,
Sir Isaac Newton, and Edmond Halley,of comet fame, all entreated
the moon and stars for help. Palatial observatories were founded
at Paris, London, and Berlin for the express purpose of determining
longitude by the heavens. Meanwhile, lesser minds devised
schemes that depended on the yelpsof wounded dogs, or the
cannon blasts of signal ships strategically anchored, somehow,
on the open ocean.
In the course of their struggle
to find longitude, scientists struck upon other discoveries
that changed their view of the universe. These include the
first accurate determinations of the weight of the Earth,
the distance to the stars, and the speed of light.
As time passed and no method proved
successful, the search for a solution to the longitude problem
assumed legendary proportions, on a par with discovering the
Fountain of Youth, the secret of perpetual motion, or the
formula for transforming lead into gold. The governments of
the great maritime nations- including Spain, the Netherlands,
and certain city-states of Italy- periodically roiled the
fervor by offering jackpot purses for a workable method. The
British Parliament, in its famed Longitude Act of 1714, set
the highest bounty of all, naming a prize equal to a king's
ransom (several million dollars in today's currency) for a
"Practicable and Useful" means of determining longitude.
English clockmaker John Harrison,
a mechanical genius who pioneered the science of portable
precision timekeeping, devoted his life to this quest. He
accomplished what Newton had feared was impossible: He invented
a clock that would carry the true time from the home port,
like an eternal flame, to any remote corner of the world.
Harrison, a man of simple birth
and high intelligence, crossed swords with the leading lights
of his day. He made a special enemy of the Reverend Nevil
Maskelyne, the fifth astronomer royal, who contested his claim
to the coveted prize money, and whose tactics at certain junctures
can only be described as foul play.
With no formal education or apprenticeship
to any watchmaker, Harrison nevertheless constructed a series
of virtually friction-free clocks that required no lubrication
and no cleaning, that were made from materials impervious
to rust, and that kept their moving parts perfectly balanced
in relation to one another, regardless of how the world pitched
or tossed about them. He did away with the pendulum, and he
combined different metals inside his works in such a way that
when one component expanded or contracted with changes in
temperature, the other counteracted the change and kept the
clock's rate constant.
His every success, however, was
parried by members of the scientific elite, who distrusted
Harrison's magic box. The commissioners charged with awarding
the longitude prize- Nevil Maskelyne among them- changed the
contest rules whenever they saw fit, so as to favor the chances
of astronomers over the likes of Harrison and his fellow "mechanics."
But the utility and accuracy of Harrison's approach triumphed
in the end. His followers shepherded Harrison's intricate,
exquisite invention through the design modifications that
enabled it to be mass produced and enjoy wide use.
An aged, exhausted Harrison,
taken under the wing of King George III, ultimately claimed
his rightful monetary reward in 1773- after forty struggling
years of political intrigue, international warfare, academic
backbiting, scientific revolution, and economic upheaval.
All these threads, and more,
entwine in the lines of longitude. To unravel them now- to
retrace their story in an age when a network of orbiting satellites
can nail down a ship's position within a few feet in just
a moment or two- is to see the globe anew.