An article based on two papers that are published this month in the Proceedings: paper 4312 S entitled ‘The effect of a back-e.m.f. nonlinearity on responses of a secondorder position control system’ by F. Fallside andM. R. Patel, and paper 4273 S entitled ‘Application of the second method of Lyapunov to the stability of certain position control systems containing a back-e.m.f. nonlinearity’ by F. Fallside and J. O. C. Ezeilo. The papers will be read before a meeting of the Science and General Division on the 9th December 1963 at Savoy Place. Dr. Fallside and Mr. Patel are in the Department of Engineering, University of Cambridge, and Dr. Ezeilo is in the Department of Mathematics, University of Ibadan.