NavList:

   

Reply

I did not completely recognize the setup that George referred to,
when reading Peter's description.

I wonder if the method is similar to the principle of Sperry's North
seeking gyro-compass?
Here, if a gyro spins in the local vertical direction, it will tilt off
vertical,
until its erecting method reduces the corrections need by orienting it
to the geographic north axis.   So this device needs to sense the
steady rotation of the Earth. Which can be defeated in polar latitudes,
  by motion contra the Earth's spin.

Brian


At 07:13 PM 9/15/02, Peter Fogg, you wrote:
>'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.

Brian Whatcott
   Altus OK                      Eureka!

   

Reply