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Douglas Denny wrote, in ]9852]-

"In the 1950s (or was it 60s - can't remember)  the Antartic expeditions
using caterpillar tracked vehicles to get to the Sotuh Pole used a mirror
set-up in the driver's vision of the front vehicle, to enable him to look
backwards so the driver could look back along his track made in the snow,
and thus keep a straight line ahead.  It was very effective apparently as he
was making a continuous back-bearing on his own tracks with which he could
see immediately if he veered off track."

========================

I presume Douglas Denny refers to 1958, when the trans-Antarctic expedition
were trying to get from, not to, the South Pole, in the last stages of their
crossing. This took the party near the South Magnetic Pole, when their
magnetic compasses (at least, those aboard their tracked vehicles) became
useless, and with sky overcast, the Sun position was of no help..

My reading of the technique, as described by Fuchs and Hillary in their book
"The crossing of Antarctica", bears little relation to that description
given by Douglas Denny above. I can find no mention of using alignment, in a
mirror, with the vehicle's own tracks, as he described. If it's there, or
perhaps in an account of another expedition altogether, a reference would be
helpful.

Having somehow established an intended direction and marked it with a pair
of flags, they continued it indefinitely by having a collection of marker
flags carried in the leading vehicle. Before the flags behind them had
disappeared from sight, one of the team would get out and place a new marker
precisely aligned with those that had gone before. In this way, they kept a
chain of four flags constantly in view. As I see it, three flags would have
sufficed, but no doubt four provided belt and braces.

The flags, when no longer needed, were collected by the trailing vehicle,
and eventually recycled.

In this way the straight path could be extended on and on, and a large
radius of curvature could be maintained. The angle-of-bend, at each new
flag, was kept small, being limited (in radians) to the error in aligning
each new flag with its predecessors, divided by the spacing between the
flags. Hopefully, that error would not always be in the same direction, but
inevitably, an error in direction would accumulate. However, the sky cleared
after about 100 miles of travel had been accomplished by this technique.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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