The Longitude Question

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The Longitude Question
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1490-1945

• European exploration and colonial expansion is at
  its height
• British maintain worldwide dominance
• British Royal Navy dominates the seas

Lands at any time part of the Brittish
Empire shown in red. http//www.regiments.org/nati
ons/
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• Latitude is easily determined by looking at the
  suns angle at noon.

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• Using a sextant, navigators could precisely
  measure the angle of the sun above the horizon at
  local high noon. This angle could be used to
  determine ones latitude.
• The sextant could also be used to take lunar
  measurements to find longitude but the
  calculations were too difficult for most to
  perform.

http//en.wikipedia.org/wiki/Sextant
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• During cloudy days and nights, looking to the
  heavens for guidance was fruitless.
• Sailing for a few days in cloudy weather
  degraded information about the ships position.
• Land sightings, current, and weather changes
  were used to guide ships.
• Galileos method of using the location of
  Jupiters moons was impossible if the ship
  pitched and rolled.

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In 1707, five British ships sink within minutes
after running onto the rocks of the Scilly Isles

• 1647 sailors die
• Multiple treasure chests of great monetary value
  lost.

Scilly Isles
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Wreck was due to the difficulty of determining
longitude at sea

• A sailor and unofficial navigator on board warned
  Admiral Shovell of the ships proximity to the
  Scilly Isles.
• For questioning the Admiral the sailor was
  hanged, according to some reports.

Sir Clowdisley Shovell Admiral of the
Association http//www.geocities.com
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In 1714 the British government passes the
Longitude Act which

• Offers a prize of 20,000 to anyone who can come
  up with a solution to find longitude at sea
  within ½ degree (35 miles at the equator).
• Creates a Longitude Board to evaluate solutions.
• The Longitude Board is comprised primarily of
  astronomers and mathematicians.

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John Harrison - Clock Maker Extraordinaire

• Son of a Carpenter
• No formal education
• Carpenter and Mechanic by trade
• Keen understanding of materials, i.e. metals and
  woods
• Interested in creating a chronometer to solve the
  longitude problem.

https//eee.uci.edu
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Early Achievements of Harrison

• Built a clock entirely out of wood at the age of
  20. A self lubricating clock, where lubricants
  bleed out of the woods.
• Invented the Gridiron Pendulum. This was a
  pendulum constructed of alternating dissimilar
  metals. The thermal expansions of the two metals
  cancelled out, thus maintaining a constant
  pendulum length.

Brass and Iron Rods
http//physics.kenyon.edu/
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What is a chronometer?

• A precision time piece that keeps the time at a
  fixed location. This time acts as a reference
  point for determining longitude.
• Knowing local noon at sea and the time at
  Greenwich England, navigators could determine how
  many minutes or miles they were from Greenwich,
  England.

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Chronometers had to keep time even when the ship
tipped, pitched and yawed.
1810 Chronometer mounted on Gimbels http//www.ste
dmundsbury.gov.uk
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Precision Pendulum Clocks failed at Sea

• Accurate time is kept by the oscillations of the
  pendulum.
• Frequency (cycles/sec) are determined by the
  length of the pendulum and force of gravity
• f (1/2p) v(g/L)
• Pendulum clocks require a constant gravitational
  force, in other words- stable ground

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John Harrisons H1Completed when he was 42
Two independent Pendulums
This took seven years for Harrison to
build. (Courtesy National Maritime Museum,
London)
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The Board doubts a mechanical instrument can
solve the longitude problem

• Board demands a sea trial of H1
• Board grants Harrison 500 to improve H1
• Eventually Harrison develops a small timepiece,
  the H4 at the age of 68

The H4
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Multiple trials

• H4 goes to Jamaica and measures longitude to
  within 2 miles.
• Board claims result was luck
• H4 goes for a second trial, and measures location
  of Barbados within 10 miles.
• Board awards Harrison 10,000 but demands more
  testing and detailed plans so that device can be
  reproduced by other clockmakers.

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Foul Play

• Nevil Maskelyne was appointed Astronomer Royal
  and sits on the Board of Longitude
• Maskelyne develops a less accurate solution
  (barely within the Longitude Acts limits) based
  on the lunar distance method, which requires many
  calculations from viewing the moon against the
  stars.
• Conflict of Interest
• Maskelyne claims Harrisons H4 is inaccurate and
  results are just luck.

Wikipedia
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Royal Intervention

• King George III finally intervenes on Harrisons
  behalf and has him righted.
• In 1773, when he was 80 years old, Harrison
  received 20,000 from Parliament for his
  achievements, but he never received the official
  award (which was never awarded to anyone).
• Harrison struggled with the Board for over 38
  years.

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Timepieces Today

• Quartz clocks use an electronic oscillator that
  is made from a quartz crystal. Accurate to 10
  seconds/year.
• Atomic clocks uses the resonant frequency of
  atoms. Accurate to 1ms/year

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Some sources
TV Movie - Longitude
http//www.youtube.com/watch?vROz0-4ymuXQ You
Tube John Harrison His Clock and the Longitude
Problem