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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Pendulous gyroscopes
From: Peter Fogg
Date: 2002 Sep 16, 10:13 +1000
From: Peter Fogg
Date: 2002 Sep 16, 10:13 +1000
'Peter. I did my PhD on pendulous gyroscopes. Part of my field wok was made at a station in latitude S80 degrees. I found the latitude of this station from my gyroscope observations to within two minutes of arc. Of course nothing works at the pole. George.' This was in response to a query from Walter about whether polar explorers used pendulums (please excuse any inaccuracy here but I can't find this posting). Was interested enough to seek more information (over the phone) and this is my summary of what I found out: A pendulous gyroscope spins at about 20,000 rpm at the end of a fine thread. As it is lowered it oscillates in a plane parallel to the direction of (true) north. It is accurate at low and medium latitudes, but at high latitudes the period of oscillation increases and it becomes progressively less accurate (which explains why it was a feat to find 'the latitude of this station (S80 degrees) from my gyroscope observations to within two minutes of arc'. At the pole it doesn't work at all, 'just flops about'. It has practical uses in surveying, and my George has used it in surveying in underground mines where below ground workings can be correlated to above ground ones without any direct link between them. He also mentioned that while on the Antarctic mainland he developed tables for the observing of daylight stars through the telescope of a theodolite, which is feasible for the most bright stars. I asked whether in this case binoculars could be used for observing daylight stars, the problem is firstly 'you need to know where to look' and secondly, such observations are difficult because of the instability of the hand-held binoculars. This is why his instrument of choice for land based observations is the theodolite, rather than a hand-held sextant. Obviously these observations in Antartica were made in fine weather with full support, I don't mean to compare them with those of polar explorers. Any mistakes here are most likely to be mine.