The Tumbling Weir

At Ottery St Mary where we are staying the night. The full history is on my extra. Fascinating. In 1788 there was a plan to build a "manufactory" for the carding and spinning of wool. the older arrangement didn't provide a sufficient head of water, so the level of water in the mill basin had to be raised by 8 feet.  the water level was maintained by the circular "tumbling weir" which (a bit I think, like the point loading of a stiletto heel) meant that the force was equal to a significantly larger linear weir.