Shape of the World

1
Shape of the World

• The first High-Tech Superpower Rivalries

2
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.

3
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

4
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-1700s were there
  circumnavigations largely aimed at exploration
• Drake and his fellow pirates would now be called
  state-sponsored terrorists

5
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, cant
  raise crops, etc.)

6
A Geographical Oddity
7
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

8
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

9
The First Commercial Round-the-World Traveler

• By the 1600s 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

10
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)
• 1600s cargo far more valuable than ship
• My ship came in - one good voyage could set you
  up for life.

11
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

12
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

13
Why Compasses Dont 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

14
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

15
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.

16
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.

17
Astronomical Methods

• Eclipses of Moon Everyone who sees the Moon sees
  the same thing
• Too rare for most purposes
• Eclipses of Jupiters moons frequent but hard to
  observe
• Method never panned out

18
An Unexpected Spinoff

• The Dutch astronomer Roemer found eclipses ran
  early or late
• Discrepancy time for light to cross Earths
  orbit
• First evidence that light had a measurable speed

19
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?

20
Anything at All
21
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 Earths interior
• The distortion is about 1/298 of the Earths
  diameter - 29 miles out of a diameter of 7927
  miles.

22
How do you Measure Latitude on an Elliptical
Earth?
23
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

24
So Who Cares?

• This sort of accuracy is useful for steering
  ICBMs or using GPS systems
• What good was it in the 1700s?

25
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!)