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Fred Hebard wrote in relation to the Australian explorer Augustus Gregory

"Also, perhaps Thompson was not the best of lunarians.  Kieran Kelly
last year or so posted a series of lunar observations taken by an
Australian explorer that were exquisite.  I can't imagine that the
distance cleared from those would have been in error by more than 0.1
or 0.2' of arc, given an accurate sextant."
And
"Augustus Gregory. This was about 50-60 years after Thompson. I don't think
sextants improved much in the intervening period but the quality of lunar
predictions probably did. It could be that Gregory was just that much
better than Thompson. Thompson was blind in one eye but I don't know if
the vision in his other eye was impaired in any way."
I agree with Fred's comments and have been following this topic with
interest. If any other list members would like to examine the paper he
mentioned it can be found at:
http://www.ld-DEADLINK-com/
As I have pointed out many times before on this list, land navigators were
sometimes expert lunarians and developed their own methodologies and
techniques. I have led four expeditions in outback Australia relying on maps
produced by Gregory 150 years ago using longitudes derived from lunars. He
shot both the lunar distance and the altitudes of the bodies in the same
process. Unlike L & C he sat down and worked lunars out in the field.
To anyone interested in 19c technique I urge you to read the Gregory paper.
Also on this topic Frank  Reed wrote: "But something that might not be so
obvious is that dead reckoning is simpler at sea since it consisted of long
legs on constant headings. At least there aren't any currents on land!"
I have used both horses and camels in desert conditions without landmarks
following a compass bearing. Dead reckoning is easy under these conditions
because:
1) There is no set or drift - it is easy to steer the animals in a straight
line.
2) All pack and riding animals when organised in a "string" walk single file
in a straight line behind each other
3) All walk at a remarkably constant speed. Camels 4km/5km per hour
depending on ground, heat and scrub ditto for horses except they walk about
6km per hour. Well handled the animals will maintain these paces/speeds day
in and day out.
After a 30 km march in desert country using a compass, I am very
disappointed if I am out by more than 1km (6/10 mile) at the evening camp
(checked using GPS).
Kieran Kelly
Sydney
Australia

   

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