[Offprint.] The Wilde Lecture. V. The Mechanical Principles of Flight. By the Rt. Hon. Lord Rayleigh, F.R.S. Delivered February 13th, 1900.

26pp., 12mo. Stitched. In remains of original printed wraps. On aged paper, in chipped wraps, with several leaves loose. An important work in the history of eronautics by one of the great experimental physicists of the nineteenth century. Excessively scarce: no copy of this offprint in the British Library or on COPAC. 'In this lecture Rayleigh discusses the method of calculating the mechanical forces on a plane presented obliquely to a current of air, so far as this can be done. At best, the calculation is very incomplete. He describes a simple method of experimenting on the forces at various angles by means of a kind of many-bladed propeller which could have the various blades set at different angles so as to neutralize the tendency to rotation when the propeller was carried forward. He then considers the problem of the helicopter or flying machine maintained by a vertical screw'.