Duplex windmill
A windmill that waves at you
This is a sectional windmill, in which the blades move in and out, flapping like wings. There is no vane on this windmill design, because it uses an offset balance weight. This means that the mill is designed to be set at a particular speed, and if it exceeds that speed, it shuts down due to the blades becoming vertical and no longer catching the wind. This windmill is extremely rare and is a copy of a Halliday mill from the 1840s.