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Subject: Pendulous gyroscopes
From: Peter Fogg (ffive@XXX.XXX)
Date: Sun Sep 15 2002 - 20:13:29 EDT
'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.
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