The Sinclair Harding Navigation Clock

 

Longitude  

Today when we look at a globe of our planet, we may notice the artificial lines that trace its surface, the lines of latitude running parallel to the equator and the lines of longitude that arc between the poles. For those of us that travel by armchair or commercial airlines, these lines will have no meaning and limited value. They neither inspire us nor enhance our journey in any way.

For the pilots of our planes and the computer navigation systems, these lines are the key to getting from A to B, from London to New York, from Sydney to Nairobi.

For the great explorers of the last millennium, who effectively left their countries behind to literally travel to uncharted waters, these directional lines were crucial to either finding a new land or losing track of one’s place on the planet. In some cases, navigational error cost numerous lives as ships ran aground, sources of food and water were missed, cargoes were lost and opportunities to claim new territories were wasted.

A catastrophic event occurred when two thousand men lost their lives as four British warships sank upon the rocks of the Scilly Isles in fog one night in 1707. Their failure to accurately chart their longitude and therefore know their precise location was the cause of their demise.

Loss of life was one thing - economic loss was another. The loss of ships, merchants, cargo and treasures unsettled empires to such an extent, the British Parliament in 1714 established the Longitude Act and a healthy prize to prompt a solution. Other countries and regions such as Spain, France, the Netherlands and Tuscany also offered prizes. Calculating Longitude was considered to be a key competitive advantage in owning the seas and the treasures it could provide. The Longitude problem had existed for centuries and now the race was hotting up to find a solution.

Calculating latitude was a relatively easy task. This could be accomplished through measuring the length of the day, the height of the sun or in reference to known stars seen in the night sky. Columbus’ famous voyage to America was simply plotted as ‘sailing the parallel’ directly west.

The measurement of longitude meridians was a different matter and was totally reliant on the measurement of time. The key to knowing your longitude was to know the exact time in known places of known longitude. The time difference was then calculated into a geographical location. Errors in the measurement of time were multiplied into errors in the measure of your location.

At the time, clocks were not suited to the task because they simply weren’t accurate enough or stable enough to counter the swaying decks on a ship in the ocean. More importantly, clocks had not been designed to counter variations in temperature that affected the components and the accuracy of the timepiece.

Today, we have the luxury of being able to buy a wristwatch for less than $10 that loses less than a second each month. In contrast, in the mid 1500’s, the best available timepieces were only accurate to within 15 minutes per day. This would be considered completely unacceptable today and it was hardly suitable either for a long ocean voyage that required days of extrapolation of minutes and seconds to determine the longitudinal location.

Furthermore, the design of these clocks was based upon the pendulum which was made them even less suited to the rolling deck of a sailing ship.

To put it in context, solving the ‘Longitude’ problem had been such a concern for such a significant period of time that it was considered to be a holy grail, akin to developing a perpetual motion machine. For many, a solution was considered impossible. This was the great technological question of the time, comparable in today’s terms to finding a cure for cancer.

This sea clock was inspired by John Harrison, who won the Board of Longitude Prize established by the British Government in the 18th century for a clock, which could accurately tell the time at sea, and hence establish a ship's longitude at any moment.

As a pendulum is useless on a boat, and as a result, John Harrison invented the unique twin balance arms and grasshopper escapement. 

In 1714, the British Government passed an act offering an award of 20,000 pounds for any useful method of finding longitude at sea.  The act also established a permanent body of commissioners charged with supervising all competition for the award, which became known as the Board of Longitude. 

Whereas latitude at sea had always been established by simple observation of the sun and other heavenly bodies, the method of arriving at one's destination had been to sail until the latitude of the destination had been reached, then to run along it's parallel.  Computing longitude by dead reckoning necessarily involved considerable and growing uncertainty of a ships position.   

A watch with which to tell the time accurately affords a simple and complete solution to the problem.  A ship's longitude is the difference between the meridian she happens to be on and the standard meridian - say Greenwich.  She could establish her local time - the time of her meridian - by comparatively simple observations, and if she knows Greenwich time, the difference gives her longitude.   (National Maritime Museum, Greenwich)

John Harrison

John Harrison spent six years from 1729 until 1735 in building his first marine timekeeper.  This historic machine is preserved in full working order in the Maritime Museum at Greenwich and is considered one of the greatest horological achievements.  Harrison went on to build four further timekeepers, ending with his pocket sized marine chronometer.  His efforts were finally rewarded by receiving the Copley Medal in 1749, in recognition of his most important work.  It is the highest scientific distinction that the Royal Society can bestow. 

The Meccano replica of John Harrison's clock embodies two of the most important features of his first sea clock.   The linked balance arms, which give the clock a visually fascinating, restful and attractive quality and the unique frictionless 'grasshopper' escapement with the subtle lock and release action of the pallets.  

Although the clock is not an exact replica of the Harrison Number 1, it does follow quite closely the design of Sinclair Harding, a leading firm of clockmakers who originally had premises in Cheltenham and the clock is still being made elsewhere.  A similar design has also been produced by Asprey of New Bond Street, London.

This Meccano Navigation clock was first shown at Skegness in 1988.  It won first prize the Issigonis Shield and was subsequently written up in the North Midlands Meccano Guild magazine.    While the present design uses the same escape wheel and pallets, the new clock differs markedly from its predecessor.   The main change in the simplification of the complicated springs and levers which control the pallets.  These have been reduced to a single spring which performs three functions - that of placement of the pallet against an escape tooth, recoil and escape wheel reverse rotation.

The whole movement is supported in pivot bearings and on roller bearings, all of which are made from Meccano.   The entire clock frame has been re-designed to give a more elegant appearance.

The power supply is from an electric motor whose weight is the driving force as described by John Wilding in CQ magazine.  The motor is activated by a mercury tilt switch and the motor is arranged in a planetary fashion to rotate around the drive gear.   The motor is triggered every 40 seconds and AA batteries provide enough power to drive the mechanism for months.  The clock is easy to time and is a reliable timekeeper. 

Full plans to build this clock (MP 139) can be obtained from MW Models, Henley-on-Thames