Abstract: A turbine with a vertical axis of rotation is described, with particular reference to a wind powered embodiment. It is advantageous to ensure that a turbine rotates at a substantially constant speed despite variations in the driving force and to ensure that the turbine is not damaged when the driving force is excessive. The turbine includes a plurality of turbine blades arranged about a central axis, with each turbine blade being pivotally mounted towards its outer periphery about an axis substantially parallel to the central axis. A biasing element biases the inner periphery of the turbine blades towards the central axis. As the speed of rotation of the turbine increases, the blades swing out of the wind and there center of gravity moves away from the central axis, tending to slow the speed of rotation.