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John Rimmer Scientific Instruments
Transcript for Jim Smith - sextent
This is the sort of instrument that they made. This is the sextant which is absolutely marvellous and used by ships across the world. Until you’ve actually sailed somewhere you don’t realise how big the world is or the seas. That, as I say, that was from number 27 Wapping and here’s the old original company logo etc, Marine Opticians. They must have been magnificent men; all this was spun on old treadle lathes and they’d swap the treadles over, put another wheel on and it’d go faster. It was fantastic. A sextant, you can only take readings on one sixth of the earth, so at any one time you can only get to the horizon which works out at one sixth which is 60 degrees and that’s all this can navigate, but that in navigation terms means a lot of miles. If you put all the instruments together, you could actually see then to the horizon (Jim demonstrates with the sextant), and you’d take it up to the sun and at the same time move your quadrant which again is locked down so you can just move your quadrant to take your reading from the sun. So you start off with altitude, then you’ve got your longitude and bring it straight in as soon as it cuts, but this is from the lowest part of the ship by the way, you’d lock it there, take a reading from the quadrant and you can put it down on your chart. It’s as simple as that really but it’s very scientific as well.