The Longitude Question
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/nations/
Latitude is easily determined by looking at
the sun’s angle at noon.
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.
http://en.wikipedia.org/wiki/Sextant
The sextant could also be used to
take lunar measurements to find
longitude but the calculations were
too difficult for most to perform.
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 ship’s position.
Land sightings, current, and weather changes
were used to guide ships.
Galileo’s method of using the location of Jupiter’s
moons was impossible if the ship pitched and
rolled.
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
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
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.
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
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/
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.
Chronometers had to keep time even
when the ship tipped, pitched and
yawed.
1810 Chronometer mounted on Gimbels
http://www.stedmundsbury.gov.uk
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) * √(g/L)
► Pendulum clocks require
a constant gravitational
force, in other wordsstable ground
John Harrison’s H1
Completed when he was 42
Two independent
Pendulums
This took seven years for Harrison to build.
(Courtesy National Maritime Museum, London)
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
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.
Foul Play
► Nevil
Maskelyne was appointed
Astronomer Royal and sits on the Board Wikipedia
of Longitude
► Maskelyne develops a less accurate
solution (barely within the Longitude Act’s
limits) based on the lunar distance
method, which requires many calculations
from viewing the moon against the stars.
 Conflict of Interest
► Maskelyne
claims Harrison’s H4 is
inaccurate and results are just luck.
Royal Intervention
► King
George III finally intervenes on
Harrison’s 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.
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
Some sources:
TV Movie - Longitude
http://www.youtube.com/watch?v=ROz0-4ymuXQ
You Tube – John Harrison His Clock and the
Longitude Problem