Dear Robert,
Many thanks for your suggestions below. Whilst recognising the problems
suggested in your first paragraph (my own cottage (late 16th c) is a case in
point), it doesn't wash with the construction of this hemp retting pool.
The builders have very accurately put a 2 degree outward lean on the walls,
and have ensured that the buttresses are built into the walls, and not
added. The measurements of the walls are:
N/S walls: 10.2M. Angle of internal wall: 115 degrees.
W/E walls: 12M. Angle of internal wall; 65 degrees.
Wall height 5.2M Wall thickness 1.2M
All this is just too precise to be an example of old builders' inability to
understand geometry and I would suggest for such an early date they
understood the geometry of this construction very well indeed.
Your suggestion regarding site space constrictions is far more likely, the
pool having been built within what are now fossilized strip fields. However,
as the strips surrounding the pool run north/south, it would have been just
as easy, infact far simpler, to have built the pool as an north/south.
west/east oblong.
The pool is built upon steeply rising ground and the builders have cut out
of the hillside a large working platform. The waste from this excavation was
placed just below the west/east lower wall to act as a large barrier and to
stabilize the south end of the platform. The walls were then built upon this
level working platform and backfilled on the non water side with rammed
clay.
The very nature of this construction suggests the parallelogram shape to be
purposeful. But why?
Thanks again for your thoughts.
Trevor
----- Original Message -----
From: "Robert Waterhouse" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 22, 2008 3:51 PM
Subject: Re: Parallelogram v Oblong
> 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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