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Re: The repeating reflecting circle.
From: George Huxtable
Date: 2005 Jan 19, 12:13 +0000
From: George Huxtable
Date: 2005 Jan 19, 12:13 +0000
Thanks to Alex for countering my speculation, that Simms' book might have been referring to a different sort of dip. Clearly, it wasn't. He sais- >I site the history of the dipmeter from Simms book: > >"When the late professor Vince was engaged in making >observations upon extraordinary refraction in Ramsgate, >Mr Throughton contrived and constructed for his >use an instrument which he >called a Refraction-Sector. > >About five years afterwards, when preparations were making for >the first of the late North Polar Expeditions, >Mr Troughton was applied to by the late Dr Wollaston, >to make him an instrument on the principle of back observation >with the quadrant, to send with the expedition, to measure >the dip of the horizon; but upon Mr Troughton's producing his >Refraction-Sector, which was as well adapted to Dr. Wollaston's >purpose as that for which it was devised, >the Doctor immediately ordered >one to be made for him, and named it a Dip-Sector..... ============= That's interesting. Barrow, at the Admiralty, in the mid-19th century, was sending expeditions (especially naval ones) off around the World, particularly to Polar areas. Wollaston was a physicist specialising in optics. I remember the name, but not the purpose, unfortunately (birefraction?) of the "Wollaston prism", from my schooldays. Barrow put the provision of instruments into Wollaston's hands. As a result there are many natural geographic features, particularly Arctic / Antarctic ones, named after Wollaston. Perhaps the explorers were particularly grateful for well-chosen instruments. More likely, on such voyages of discovery, they simply ran out of names, after using up their wives' names, and the Admiralty Commisioners' names, and perhaps a sponsor or two, Yes, even then, sponsorship paid off: for example, Boothia peninsula, in the Arctic, was closely related to Booth's Dry Gin. But I digress. As I understand it, temperature gradients above the horizon can be particularly strong and stable in the Arctic / Antarctic. I have read an account of a sledge expedition, trudging over what turned out to be a perfectly flat plain, in which it appeared that they were forever in the bottom of a shallow bowl, with the horizon appearing to slope upwards in all directions; very apparent to the naked eye, and rather disheartening. So a dipmeter could well have been an important item to Arctic travellers, and perhaps to the Soviet Arctic fleet. It will be interesting to learn about the Troughton refraction-sector. Rather then measure front and back horizons, as is done with a quadrant fitted for back-observation, and capable of looking over the observer's head, I wonder if instead it measured the vertical angle between two views of the horizon, to the observer's left and right. George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================