Travel Reference
In-Depth Information
man who could solve the problem to within thirty nautical miles of
accuracy. They then set up the Board of Longitude to examine the
'solutions' which came flooding in. Despite the hundreds of ingeni-
ous ideas and mechanisms which were submitted, half a century
passed without anyone winning the reward.
The key to the calculation of longitude is time. If you know what
hour it is at the place where you are now and also at your origin-
al point of departure; if you subtract one figure from the other and
multiply the result by fifteen, you know how far east or west of your
starting point you are, measured in degrees of longitude. It only then
remains for you to add or subtract the difference between the lon-
gitude of your embarkation point and the Greenwich meridian to fix
your absolute longitude. That is the easy way. Unfortunately, it was
not available to sailors in the 1760s. Or, rather, it was only just begin-
ning to be available. To make the necessary calculations an accurate
chronometer is essential: one that is impervious to the erratic move-
ments of a ship and to variations in heat and humidity. Such sophist-
icated instruments were just on the point of being perfected.
In 1728 a thirty-five-year-old horologist by the name of John
Harrison arrived in London with a design for a new clock. He de-
voted the rest of his long life to perfecting it. During that time he
made a succession of instruments. The first was cumbersome and
expensive but its successors were progressively more manageable -
and accurate - and a pocket chronometer tested on a trip to Barba-
dos in 1764 enabled longitude to be calculated to within ten miles.
The terms of the government's offer had obviously been met but it
took the now aged Harrison another nine months to induce them
to pay up. Meanwhile similar work had been done in Paris, where
Pierre Le Roy produced another type of chronometer in 1765. The
principles had been established but it was still a further twenty
years before ships could be issued with inexpensive, standard chro-
nometers.
