John Harrison exhibition in Leeds Museum
I was approached in early 2012 by the Leeds Museums and Galleries to make a 1 metre diameter compass tablet to sit in the floor of the Leeds Museum as part of the John Harrison exhibition.
Who was John Harrison?
For many centuries the dilemma of not being able to accurately determine longitude at sea had cost nations a fortune in lives, ships and cargoes. In 1714 the Longitude Act was launched by the British Government, offering £20,000 for a practical solution. John Harrison, a Yorkshireman and carpenter by trade, built a number of timepieces, which provided the practical solution the government were looking for. His early long case clocks and later sea chronometers were made of wood, essentially using two species. Oak for the moving wheels, and lignum vitae for the bushes that the wheels revolved around. Lignum vitae has natural wax within its core structure, thus providing the all-important lubrication to naturally maintain constant operation of the moving parts. Today, some 300 years later, his clocks and early chronometers are still accurate to less than 5 seconds a month! He also invented the ‘grid iron’ (Harrison’s name for a bi-metalic strip) a way of using two contrasting metals of brass and steel to counteract expansion and contraction between summer and winter. Today we find these in every household where thermostats control temperature in appliances such as electric kettles, boilers etc. Eventually, Harrison built his final timepiece, a watch, which after many trials and tribulations with the longitude board, was eventually awarded the longitude prize.
Harrison showed the world how to use the fourth dimension – ‘time’, in a three dimensional world. By always knowing what time it was at the home port, Harrison’s sea clock could always calculate the time difference. Every four minutes of time was equal to 1° east or west of longitude. Therefore every 15° that one travels eastward, the local time moves one hour ahead. Similarly, travelling West, the local time moves back one hour for every 15° of longitude.
Therefore, if we know the local times at two points on Earth, we can use the difference between them to calculate how far apart those places are in longitude, east or west.
Seamen always knew the latitude position (north to south) by using a sextant on board ship to measure the angle of the sun. At noon, for instance, the sun is measured at 90°, therefore seamen could plot their position with consummate accuracy to the degree, minute and second. Today, GPS (Global Positioning System) work on exactly the same principle. John Harrison was light years ahead of his time, and its remarkable, yet inspirational, that with such a humble background he was able to build practical solutions that involved advanced scientific and engineering technology.
I decided to make full use of my craft and use the same two woods used by Harrison, namely oak and lignum vitae. The oak was not a problem, but to obtain lignum in the veneer form was problematic. Eventually a sale of a set of bowls (used in bowling) going cheap on eBay, solved the dilemma. One bowl ended up as veneers, after passing it through a band saw. As a point of interest Lignum vitae is the densest timber on the planet. It is totally waterproof, and as such, if placed in water – it sinks.
The 16 segments of oak radially placed around the clock, show the grain pointing into the centre. I was asked to use a 18th century font for the letters and numbers depicting longitude and latitude. The border veneer is Madrona burr, used purely for decorative reasons. The black dots placed between the four quadrants NSEW are the intermediary bearings. I used a large home-made trammel to create the compass and map the bearings to achieve accuracy.
I decided to use fish glue for this project. Its a protein glue, and today made from the swim bladders of cod fish. Like animal glue it is completely reversible, but has the added benefit of being able to be used cold. The curing (setting) time is 12 hours. We left the panel in the platen press overnight. It was good to be back at the college, where I taught marquetry some twenty years earlier. Picture shows cabinet making course lecturer, Richard Jones, spreading the fish glue while I have the easier task of applying it. The backing veneer of mahogany can be seen to the right.