Dear Trevor,
Most amusing. This appears to be a classic example of old builders'
inability to understand geometry when setting out a building or other
structure. They understood about measuring the sides of a square or
rectangle, but not about the importance of measuring the diagonals to ensure
right angles. I commonly find this sort of thing when measuring up old
houses and agricultural buildings in Devon (though the problem seems to have
been endemic). Basically they did not understand, or probably even know,
about Pythagoras! Archaeologists are taught about this when setting out
site grids (the 3-4-5 triangle, where 5 is the dimension of the angled
line).
There is another possible explanation: that the site had space constrictions
- a common problem in towns. This however only produces a parallelogram
where both boundaries are parallel, such as between a pair of burgage plots.
If only one side was squiffy, surely you would get a rhombus shape?
Hope this helps.
Robert Waterhouse
-----Original Message-----
From: mining-history [mailto:[log in to unmask]] On Behalf Of
Trevor Dunkerley
Sent: 18 September 2008 20:07
To: [log in to unmask]
Subject: Re: Parallelogram v Oblong
Dear List,
We have now excavated out the 4 corners of the 12/13rh century hemp pool at
Mine Tenement and in the north western corner the remaining pool wall is
over 5m in height. This clearly shows the need for the internal buttresses
to stop the walls falling inwards when the retting pool was emptied of
water.
However, we are completely baffled by the fact that the pool walls have been
built in the shape of a perfect parallelogram (with opposite pairs of sides
equal in length and parallel, and opposite angles equal). Why build a
parallelogram and not an oblong shaped pool?
Is this something to do with strength? We have now been able to calculate
that the pool, when full, contained over half a million gallons of water -
hence 8 internal buttresses and a 2 degree outward lean on the walls. The
pressures when emptied must have been huge.
Any good mathematicians out there who would like to comment?
Kindest regards,
Trevor
http://www.cmsmrps.org.uk - a community archaeology initiative.
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