Dear All,
Here is a cautionary tale. In summary:
NEVER believe ANYTHING without checking!
A little while ago, Doug Bateman mentioned
that there were some lines of longitude
marked in the paving of Peninsula Square
by the O2 Arena in London. You can see
these as follows...
Enter Google Maps and, into the search box,
key in:
51 30 4.75 00 00 15.91
Google allows this syntax for latitude and
longitude.
You will find yourself on the Greenwich
Peninsula just south of the O2 Arena.
Now zoom in as far as you can and you will
see a white line running roughly north-south
flanked by two black lines. Let's call this
a line-triplet. The pointer should pick out
a dark stone which punctuates the line-triplet.
This stone carries an inscription which you
can't read but I have a photograph of it at
www.cl.cam.ac.uk/~fhk1/Sundials/Misc/Stone.jpg
You will see that the inscription says:
These paving lines are
one tenth of a second
of longitude or
18.1 m apart
51°30'03"N 0°00'23"E
This is intriguing because almost everything
it says is untrue, or at best, misleading!!
Zoom out a little and you will certainly see
neighbouring line-triplets.
To get to the neighbour on the right, key in:
51 30 4.75 00 00 16.85
We are at the same latitude but 0.94" further
to the east. How does this square with "one
tenth of a second of longitude"?
Also, where on Earth does the 18.1m come from?
At the latitude of Greenwich I make it that
one arc-second of longitude is about 19.4m
so one tenth of a second would be 1.94m.
Are they lines of longitude?
Of course that is only an implication but
it is pretty strongly implied...
If you slide one of these line-triplets to one
of the vertical edges of your window you will
see that it fails to align by about 1 degree.
If they are lines of longitude they have been
pretty poorly surveyed.
Where does the 51 30 03 00 00 23 on the
stone come from?
Without knowing which coordinate system they
are using it is hard to say. If you naively
key this into the search box you will find you
land on the roof of a building.
OK, this may simply mean they are not using
the same longitude reference as Google.
Fortunately we have the roof of the Airy
transit instrument nearby for calibration
purposes and this obligingly DOES run true
north-south!! Key in:
51 28 39.96 -00 00 5.3
Yes, a minus is allowed by the syntax too.
The pointer indicates the rough centre of
the roof above Airy's transit instrument.
If you are the right kind of enthusiast,
this is the "Prime Meridian of Longitude".
The longitude quoted suggests we might try
subtracting 5.3" from the 23" on the stone.
Key in:
51 30 03 00 00 17.7
Bingo! We seem to have hit an inscription
stone. Shame it is the wrong one! I suspect
it has been moved!
I haven't been able to find documentation
about these lines from a simple search.
Maybe another reader knows about them?
All this hard-landscaping must have cost
shed-loads of money. What a pity they
didn't get it right.
Happy surfing
Frank
Frank H. King
Cambridge, U.K.
---------------------------------------------------
https://lists.uni-koeln.de/mailman/listinfo/sundial
