Meeting of the Society was held at the Royal Society of Arts on Thursday, March ist, 1923, Professor L. Bairstow, C.B.E., F.R.S., in the chair. The Chairman, in calling upon Major F. M. Green to read his paper on “ Air Travel, with Special Reference to the Helicopter,” said that many of those present would be able to> agree with the very critical review of the problem given by the lecturer, and it would be an advantage perhaps to the progress of aviation if the Society gave a technical opinion as to the value of the helicopter as a means of air travel.

The investigation summarised in the two preceding papers formed part of a rapidly carried out research which was made at the commencement of the war in order to determine whether a machine on the helicopter principle could be built, and whether, when built, it was likely to prove of any special value for belligerent purposes.

When engaged on war work as Chief Inspector for Fredk. Sage & Co. at Peterboro’, England, in the spring of 1918, I observed that when Honduras mahogany was compressed across the grain, and parallel, to the annular rings of the wood, a “first” or “natural” elastic limit was reached, after which the deflections increased more rapidly than the load, as has been commonly observed in all testing of all materials.

The object of the present paper is to give some account of certain methods developed by Joukowsky, Mises and others for calculating the forces experienced by a body of aerofoil shape placed in a stream moving in a fixed direction with uniform speed. The span of the aerofoil is supposed infinite and the cross section uniform and the motion thus becomes two-dimensional.