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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

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shape of the world

Shape of the World

The first High-Tech Superpower Rivalries

the impulse toward exploration
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
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
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
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.)
the first two three time circumnavigator
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 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
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 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
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
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
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 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
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
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

Astronomical Methods
an unexpected spinoff
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
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 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.
the race to find the shape of the 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
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
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!)