Abstract: Apparatus for detecting and reducing bowing of a rotating roll used with hot material comprises a proximity sensor mounted adjacent the surface of a roll or of a member attached thereto, and arranged to generate an electric signal which varies between maximum and minimum limit values during each revolution of the roll in dependence on any bowing of the roll, cooling means for selectively cooling parts of the roll and a bowing detection circuit arranged to receive the electric signal and provide an operating signal when the electric signal varies by more than a predetermined amount from one of the said limit values, and actuating means arranged to respond to the operating signal and operate the cooling means to cool a required part of the roll to reduce bowing.