1. Longitude
A story of life and
death, politics, mathematics, academi
c snobbery and one very talented

2. Scilly naval disaster of 1707
The biggest maritime disaster in British history
Four naval ships lost
Why?
2000 sailors died

3. Sir Cloudesley
Shovell, the
commander of this
naval fleet,
was lost!

4. Longitude error

5. Why is latitude easy …
… and longitude difficult?

6. Also known as the
“Board of
Longitude Act 1714
Longitude”
Establish: Commissioners for the Discovery
of the Longitude at Sea
Define Longitude prizes:
£10,000 for a method that could Equivalent to
determine
longitude within 60 nautical miles₤2,9 million
(111 km)
£15,000 for a method that could determine
today!
longitude within 40 nautical miles (74 km)
£20,000 for a method that could determine
longitude within 30 nautical miles (56 km)

7. Longitude problem: two
schools of thought
Measurements
and calculations
based on
catalogue of
heavenly bodies

8. Longitude problem: two
schools of thought
Post of Astronomer
Royal, seated at
Greenwich, was established

9. Longitude problem: two
schools of thought
Every hour time
difference = 15°
longitude difference … and if the local
time is determined
If the time at a specific
longitude is known

10. John
Harrison, clockmake
r
No formal training
His first clock was made
of wood!

11. Built clock with bi-metal
pendulum to retain accuracy
irrespective of temperature
variations
Inventor of the
“grasshopper escapement”

12. Problem: a pendulum
based clock cannot
work on board a
pitching ship
Harrison solved this problem
through the use of a new oscillating
movement

15. Harrison’s first
maritime clock, H1
Built between
1730 and 1735
The Board of Longitude were
impressed – the only negative
comments came from Harrison!

16. Harrison’s second
maritime clock, H2
Built between
1737Made 1740
and
for His Majesty
George The IInd
By order of a Committee
Held on 30th of June
1737
H2 was praised by the
Board of Longitude, but
Harrison was not satisfied

17. This is H3, built
with circular
balances.
Built between
1740 and 1759,
19 years!
Again, Harrison was
not satisfied!

18. Before H3 was completed, in
1755 he started to work on H4
– a revolutionary design!

19. H4 was completed in 1761.
Harrison’s son, took
the watch on a ship
that departed on
18 November 1761
and arrived in
Jamaica on
19 January 1762
The watch was only 5,1 seconds slow!

20. A second test of H4 was done in 1764
on a voyage to Barbados.
After a voyage of 47 days, H4 was
found to have an error of only
39,2 seconds!
An error less than 1000th %!
This was 3x the accuracy required to
conform to the requirements set by
the Board of Longitude.

21. The Board of Longitude decided this
result was a fluke.
Harrison was instructed to build
another clock for testing.
Harrison was told to reveal all his
secrets and hand over all his
mechanisms and design documents to
the Board.

22. Why?

23. In 1765 Rev. Dr. Nevil
Maskelyne was appointed
as the Astronomer Royal
based at Greenwich

24. Rev. Dr. Nevil Maskelyne despised
Harrison’s approach to the Longitude
problem
“The Longitude problem is a
mathematical problem, not a
mechanic’s problem”

25. Rev. Dr. Nevil Maskelyne was also a
member of the Board of Longitude
He was a proponent of the
Lunar Distance Method, a
complex process requiring
complex measurements of
the moon, three calculation
steps and extensive lookup
tables

26. He accompanied the H4 on the test
voyage – but to take measurements to
calibrate lookup tables for the Lunar
Distance Method

27. Harrison then
built H5 from
1769 till 1772
But Harrison (aged 79) had enough

28. On 31 January 1772 he had an
audience with King George III
The King’s response:
“... these people have been cruelly
wronged...”
“By God, Harrison, I will see
you righted!”
H5 was put on trial by the King himself
in 1772, and performed superbly.

29. The Board of
Longitude, however, refused to
recognise the results of this trial, so
John and William petitioned
Parliament.
They were finally awarded £8750 by
Act of Parliament in June 1773.
Perhaps more importantly, John
Harrison was finally recognised as
having solved the longitude problem.

31. The Board of Longitude
was abolished by Act of
Parliament in 1828

32. H1, H2, H3 and H4 are on display at
the Royal Observatory, Greenwich
H1, H2, and H3 are still running!