About Time!

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During our recent short break in London, we checked in our hotel around midday on the Saturday , left our bags and headed down to the pier by the Tower of London where we caught a boat which took us along the Thames to Greenwich. Our main objective was the Royal Observatory, on top of the hill in Greenwich Park.

It seemed that for most visitors the main reason for paying the entrance fee was so they could have their photograph taken while standing astride the Prime Meridian and were quite happy to queue up for 40 minutes or so to do this. I couldn’t see the attraction myself. After all the meridian goes right round the globe and there are plenty of places where you can stand with the right leg on one side and the left leg on the other.

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As for us, we were more interested in looking round the original Observatory building – Flamsteed House which was designed by Sir Christopher Wren in 1675 -  and the Time Galleries exhibition.

Flamsteed House is quite small and as it was a working building has been altered many times over the years. The most interesting, and best preserved, part was the Octagon Room, which seems to very much as designed by Wren.

Unfortunately it was difficult to take photographs due to the number of people milling around

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According to the Museum website, the Octagon Room

was designed to observe celestial events including eclipses, comets and planetary movements. However, the positioning of Flamsteed House meant that the original purpose of the Observatory could not be fulfilled from the Octagon Room. With big windows, the room was perfect for watching the sky, but not ideal for positional observations, because none of the walls were aligned with a meridian. Most important positional observations were actually made in a small ‘shed’ in the Observatory gardens

Another case of “men in sheds”!

The Time Galleries contain an exhibition about the need for accurate timekeeping and the role it plays in our everyday lives. The highlight were the three timepieces made by John Harrison.

Quite a few years ago I read “Longitude” by Dava Sobel. A best seller, it told the story of how Harrison, set out to solve the problem of how to determine longitude when out at sea. Failure to do this accurately had cost many lives and in 1714, the British Government offered a prize of £20,000 for a solution which could provide longitude to within half-a-degree. That’s a lot of money now and an absolute fortune at the beginning of the 18th Century.

John Harrison, an ordinary carpenter from Lincolnshire with little formal education and an interest in clockmaking set out to solve the problem by constructing an accurate timepiece. Not so easy when iit would be located on a ship out at sea tossed by stormy seas and in an aggressive salt laden atmosphere. Sobel’s book tells the story of how, after several attempts, he finally succeeded in constructing a practical, accurate timepiece, the first marine chronometer. Being an ordinary bloke, the Establishment made things difficult for him, but finally, grudgingly, the “Board of Longitude” awarded him the prize.

The Observatory has all of Harrison’s original prototypes on display.

This is “H1”, his first attempt. The moving parts are controlled and counterbalanced by springs so that, unlike a pendulum clock, they work independent of orientation.

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Amazingly precise for it’s time, but Harrison knew it could be improved. He managed to get some money from the Board of Longitude to refine the design which resulted in H2

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However, he realised the design was flawed as the bar balances did not always counter the motion of a ship. So he convinced the Board to let him have some more money and came up with H3.

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It incorporated two developments – a bimetallic strip, to compensate the balance spring for the effects of changes in temperature and a caged roller bearing. However, it didn’t probe accurate enough in tests. He realised he’d reached a bit of a dead end with this approach and so went back to the drawing board.

He finally came up with H4, a completely different design. Essentially a large pocket watch, 13 cm in diameter and weighing 1.45 kg. A much more practical design for taking to sea and it worked.

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The story isn’t over yet. It took another 9 years before Harrison got his prize. the whole venture had taken 43 years from start to finish.

There’s a good summary of the saga on the Museum’s website, here.

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