Shape of the World
The first High-Tech Superpower
Rivalries

The Impulse Toward Exploration
• Tantalizingly brief gap between several medieval events and the European Age of
Exploration
• China closed itself to outsiders in 1368
• China's great voyages to Asia and Africa ended in 1431
• Last ship to Norse colony in Greenland sailed in
1406
• Columbus sailed in 1492.

Circumnavigating the Globe
• Ferdinand Magellan (Spain) 1519-22
• Sir Francis Drake (England) 1577-80
• Sir Thomas Cavendish (England) 1586-88
• Simon de Cordes (Holland) 1598-1600
• Oliver Van Noort (Holland) 1598-1601
• George Spilberg (Holland) 1614-17
• James LeMaire and William Cornelius
Schouten (Holland) 1615-17

Some Observations
• Most of these voyages were for military purposes (harassing the Spanish) rather than discovery
• This pattern is very similar to the early days of space exploration
• Not until the mid-1700’s were there circumnavigations largely aimed at exploration
• Drake and his fellow pirates would now be called state-sponsored terrorists

A Geographical Oddity
• The easiest way to sail around the world is from west to east, with the wind
• Almost all early voyages were from east to
west around South America
• Objective: secrecy in entering the Pacific
• Spanish tried and failed to establish settlements at the Straits of Magellan
(weather poor, can’t raise crops, etc.)

A Geographical Oddity

The First Two (Three) -Time
Circumnavigator
• William Dampier (between 1679 and 1711) seems to have been the first to circumnavigate more than once (three times)
• Odds of surviving a circumnavigation were very poor in early voyages
• The prevention of scurvy was not discovered until around 1800

The First Two -Time
Circumnavigating Ship
• The Dolphin (1764-66 and 1766-68) was the first ship to circumnavigate the globe twice
• It took almost 250 years after Magellan for shipbuilding technology to be able to build a ship capable of surviving two voyages

The First Commercial Round-the-
World Traveler
• By the 1600’s a globe-girdling network of
European trade routes was in place
• It was rarely necessary to circle the globe
• There were only about 25 circumnavigations to 1800
• Giovanni Carreri (1693-98) sailed to Mexico, crossed overland, then booked passage across the Pacific and back to Europe

Why Did They Do It?
• Why did people risk their lives in tiny boats to trade halfway around the world?
• Nowadays: bulk cargo. Ship more valuable than cargo, but cost recovered by many voyages (Exxon Valdez: 10 million gallons =
$10 million)
• 1600’s: cargo far more valuable than ship
• “My ship came in” - one good voyage could set you up for life.

The Compass Crisis
• Compasses often pointed quite far from true north
• Queen Elizabeth offered a prize to anyone who could solve the problem
• The court physician, William Gilbert, in
1600 published De Magnete

De Magnete, 1600
• Considered the first great work on magnetism
• Gilbert deduced the overall form of magnetic fields and concluded that the
Earth had two magnetic poles
• Earth's magnetic field varies in space and time. It changes measurably in a human lifetime

Why Compasses Don’t Point True
North
• North Magnetic Pole is not at the geographic pole
• Declination in Wisconsin is nearly zero
• Declination in Maine is 20 degrees West
• Declination in Seattle is
20 degrees East

The Search For Longitude
• The distance north or south of the equator, your latitude, is easy to find in principle.
The elevation of the celestial pole above your horizon is your latitude
• Distance east and west, or longitude, is another matter altogether. Everybody on earth at a given latitude sees the same sky during a 24-hour day

Longitude = Time
• The key to longitude turns out to be time.
When it's:
– noon in New Orleans (90 degrees west)
– it's midnight in Calcutta (90 degrees east).
– It's 6 P.M. in London (0 degrees)
– and 6 A.M. in Fiji (180 degrees)
• If you have a clock that keeps accurate time and reads the time of your home port, you can determine local time from the sun and stars and calculate your longitude.

Longitude = Accurate Time
• Circumference of Earth =25,000 miles, so:
• One hour = 1040 miles at the equator
• One minute = 17 miles at the equator
• One second = 0.3 miles at the equator
• Clock has to be accurate to seconds over a span of months, on a rolling ship, in all weather and climate.

Astronomical Methods
• Eclipses of Moon: Everyone who sees the
Moon sees the same thing
• Too rare for most purposes
• Eclipses of Jupiter’s moons: frequent but hard to observe
• Method never panned out

An Unexpected Spinoff
• The Dutch astronomer Roemer found eclipses ran early or late
• Discrepancy = time for light to cross Earth’s orbit
• First evidence that light had a measurable speed

The Final Solution - A Good Clock
• One of the great technological stimuli of all time
• John Harrison, 1761
• Need high-quality steel for springs
• Need accurate tools to make gears and other parts
• With good steel and accurate machine tools, what else can you make?

The Earth is not Round
• The Earth is not a sphere - it bulges at the equator
• Newton predicted the amount of the bulge
• The exact amount provides clues about the makeup of the Earth’s interior
• The distortion is about 1/298 of the Earth’s diameter - 29 miles out of a diameter of
7927 miles.

How do you Measure Latitude on an Elliptical Earth?

The Race to Find the Shape of the Earth
• On an elliptical Earth, a degree is slightly longer near the poles
• Accurate measurements can determine the shape of the Earth

So Who Cares?
• This sort of accuracy is useful for steering
ICBM’s or using GPS systems
• What good was it in the 1700’s?

The First High-Tech Superpower
Rivalry
• Determining the shape of the Earth required the resources of a superpower (for the time)
• Effort mostly for political prestige rather than science (sound familiar?)
• The French would love to have improved on, better yet, disproven Newton
• Unfortunately, the French calculated the
wrong shape for the Earth (Mon Dieu!)