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I have just finished an excellent book that those members interested in
astronomy/surveying/terrestrial navigation/antique instruments/history or
all of the above will enjoy.

It is "Drawing the Line - How Mason and Dixon surveyed the most famous
border in America"
Edwin Danson - author.

Anyone who ever doubted the English domination of instrument manufacture,
surveying technique and astronomical excellence in the 18th century should
read this book. Specifically surveying the Pennsylvania Maryland border had
defeated a slew of pre revolutionary Americans and they turned in
desperation to the Poms.

How it was done I think would interest many of the minds on this list. Not
content with the border survey for which they are remembered they also
undertook to measure a degree of latitude for the first time in America and
also undertook the first gravity observations on the continent.

I have a couple of questions:
1) In one part of the book they refer to the use of a zenith sector for
determining the time when a star crosses the prime meridian. This is done by
allowing a star to "rise" above the horizontal wire in the telescope and
timing the interval until the star "sets" below the wire. The mean is the
time of meridian passage.

All very good but how did they see the wires in the telescopes in the days
before illumination? The book admits that scholars don't know as M and D
left no record of this mundane procedure. However Danson speculates that
they held a candle obliquely up to the object lens of the scope allowing
just enough light in to see the wires. Sounds dodgy to me. Wouldn't this
have obliterated the light from the star especially the dimmer stars.

An old surveyor friend of mine said that he remembers observations using a
zenith sector whereby the time of passage above the horizontal was measured
by the point where the star disappeared behind the wire. i.e. the star would
be visible, then it would disappear momentarily as the light from the star
was blocked by the wire, then it would appear again as it rose above the
wire. When it disappeared again the observer knew it had gone behind the
wire on the other side of the zenith. The only problem with this theory is
that some of the early instruments used spider web for the cross hairs and I
imagine you could see the light from the star through  this type of
filament. Any comments from Anyone?

2) Given the scientific achievements of these two -"A Geordie and a baker's
boy in the forests of the Iroquois" as Mark Knoffler says in his song
"Sailing to Philadelphia" - why aren't their  achievements more celebrated
in the USA. There is a vast following in America and overseas for Lewis and
Clark, who came along a considerable time after Mason and Dixon. After
reading Dansons book it would appear that these blokes would have put the
Captains in the shade.

It appears some very capable people have been overlooked in history -
Thompson in Canada, Mason & Dixon in America, Everest in India and Gregory
in Australia.

Regards

Kieran Kelly
Sydney
Australia

Kieran Kelly
Director
Australian Pastoral Holdings

6 David Place
Seaforth 2092
Sydney


ph     612 99079610
fax    612 99078232
mob  0411 261607


e mail kkelly@bigpond.net.au 


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