Longitude by Dava Sobel
Longitude, by Dava Sobel is a short but no less fascinating read. The
history revealed and timeline constructed, outline the trials and
tribulations of mariners, scientists and astronomers alike in their
quest to accurately measure longitude.
The concept of using a grid like system of coordinates to plot and chart
any spot on the earth’s surface is owed in part to Ptolemy in his work
Geographica of the 2nd century. These lines, latitude and longitude
respectively, thereby can be used to not only chart but also navigate
the open ocean with no landfall in sight. Latitude, the lines circling
the girth of the earth, is calculated simply with skyward indicators in
the positioning of the stars or sun. Longitude however began to be
calculated utilising time comparison, given the angular nature of the
lines as they circle the earth pole to pole. The mariners must have two
’times’ for their calculations, that of their current location (native
time) and that of the pre-determined port of known longitudinal
location. They needed a watch that they could carry on the boat and
accurately and consistently tell the time of their destination port. Cue
one of the greatest problems that persisted over almost 16 centuries to
stump even the greatest minds, and the man who triumphed in creating a
solution to which there was no contest and the ramifications that we
still use today.
The catalyst that formed the tipping point for the longitude problem was
the 1707 tragedy. Admiral Sir Clowdesley Shovel was the head of a
British fleet that, due to miscalculations that were prevalent at the
time, dashed and sunk four warships against the rock of Scilly Isles and
lost more than 1600 lives to the mistake. In response a parliamentary
committee was formed and the parliament in 1714 passed the 'Longitude
Act' offering £20,000 for a viable solution. The wining solution was one
that had accuracy within a singular half degree, approximately 30miles,
on a journey from England to the West Indies.
The great many ideas for solutions across the centuries were either
mechanical (clock) or astronomical. Ranging from celestial patterns,
tracking the moon's path across the sky in relation to stars, or the
four known moons of Jupiter. The mechanical clock method relied on the
time difference equation with a clock bearing the destination port time
and the local time noted at noon, thereby calculating for every hour
apart, there is 15 degrees of longitude between the ship and
destination.
Newton himself noted a small watch would be ideal however he saw the
possibility of an astronomical solution as more giving. It wasn't until
1727 when a self-educated village man of carpentry and watchmaking
skills caught wind of the prize potential. By 1730 this man, named John
Harrison, already had substance enough plans to share them with Edmund
Halley, a board member who encouraged Harrison and connected him with
another Society member who specialised in clockmaking. Five years later
Harrison had a clock (H1) that tested well on its maiden voyage of
Lisbon. Harrison, taken by the possibilities of his own idea built
another chronometer, namely H2, in just 5 years. His second clock was
given more accolades than the first however Harrison being a man of not
science but watchmaking and carpentry, was self-driven to achieve not
the best but his best, and this he took twenty years to build another
chronometer, H3.
As Harrison's instruments became more accurate and reliably more
suitable, so did the contending astronomical solutions, just as the
intrigue did for with more scientific minds wanted their idea not
Harrison's to succeed. Chiefly against Harrison was Nevil Maskelyne,
Astronomer Royal, and he pursued testing on Harrison's clocks and at
each point attempted to thwart his efforts in the name of having a more
scientific solution despite the brilliance of Harrison's chronometers.
Despite this after completion of the third watch and receiving of the
Copley Gold Medal (1749), a fourth pocket version was completed, tested
and proven on the West Indies trip that was requirement. Despite this
board did not immediately award the prize as they had in Harrison's
absence of making, become focused on other methods that proved not as
accurate but still viable. 1765 was when they finally awarded only half
the total prize and moved the goal posts again for Harrison, and
demanded he create duplicates to prove the replicability of his watches,
as well as ordering a secondary watchmaker to produce a duplicate.
Harrison would not receive the final prize amount until 1773. The true
prize More than 5,000 ship chronometers would be used by 1815.
Marine chronometers are now regarded and appreciated worldwide as
priceless collectors items. After reading Longitude, I got to see a
marine chronometer from 1841. The craftsmanship behind the chronometer
really made me want to develop the skills so that I can one day sit in
front of a historical timepiece not just in admiration, but know how to
disassemble, adjust, reassemble, and if needed make a replacement part.
This is a watchmaker's dream.
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