Sunday, 13 January 2008

The Great Theodolite

Whilst I was in Cape Town over Christmas I had the honour to visit Richard Wonnacott at the South African Surveys and Mapping Directorate, based in Cape Town.

I was last there in 1995 and found they had one of the Great Theodolites. I couldn't resist a revisit.

Richard kindly showed me round their exhibition which contains far more than just the 36" theodolite. It's a treasure trove of historical survey instrumentation varying from a very early theodolite, to a Gunter's chain, a Millionar (I'd never heard of one of those before), an MRA1, Wild T3 and T4 (which funnily enough had the labels round the wrong way but no-one had noticed for years!) and some Maclear artifacts.

There was also an interesting exhibition on the Struve Arc, put together by the one and only Jim Smith.

More on the history of geodetic surveying in South Africa can be found here.

The piece de resistance for me was seeing the Great Theodolite.

In my piece for Geomatics World recently I called it the 'Everest Theodolite' and was politely e-mailed by Jim Smith who corrected my terminology. It's one of 6 Great Theodolites ever built. The first was built for Great Triangulation of Great Britain in 1787. After this 5 further theodolites were made. The second for the Board of Ordnance (cf Ordnance Survey) (1791), the third (c1797) for Swiss Surveying, the fourth (c1802) and fifth (1830) for the East India Company for the Trigonometrical Survey of India and the final one (1867) for India but relocated to the Cape in the late 19th century. I have my dates slightly adrift but I'm grateful to both Jim and Richard for sending me papers by Jane Insley (Science Museum) which I read with interest.

The only problem with revisiting this theodolite is that I now want to see the rest! They haven't all survived. The first was melted in a fire when the Ordnance Survey HQ, Southampton, was bombed in 1940. The second is in the Science Museum, London. Scraps of the third are in private hands. The fourth is in Dehra Dun courtesy of the Survey of India and the fifth in Calcutta. And the sixth is obviously in Cape Town. Looks like I need a trip to India. wink

1 comment:

Dad said...

Thank you for the new picture