What Happens Outside.
The river Nanny flows under the bridge at the end of Shop Street. Years ago, the whole of the grassy area on both sides of the present river, and below and above the road bridge, was under water, making a very large Mill Pond. There was a weir to hold up the water across the river at about the level of the present concrete bridge, and another one up stream on the far side of the bridge.
All this disappeared some years ago when the river system was drained and the water was reduced to the height at which it now runs. About 50 yards down the path, there is a special branch of the river called the HEADRACE coming up towards the mill under the concrete bridge and into the wheel pit, where it is held up by a Sluice Gate, operated from inside the mill. Here the water is at the bottom of the mill wheel.
When the sluice gate is opened, the water rushes through under the wheel and, catching up against the paddles, drives it round. Water wheels, like this one, with the water at the bottom of the wheel are called UNDERSHOT wheels. In some cases the water pushes the wheel round from the top; these are called OVERSHOT wheels.
In some mills the water strikes the wheel about the centre; this type of wheel is called BREASTSHOT. When the water has done its work, it rejoins the river through a channel, called the TAILRACE. The wheel, which is made of iron and wood, is 15 feet in diameter, and when running normally would have turned at 15 revolutions per minute, giving 20 horse power.