Nearly twenty years have passed since the author had the pleasure of giving a paper on the same subject to this Society. Progress in the meantime as regards the means and art of flying has been not only sustained, but rapid, as is brought out by the simple facts contained in Table I. The amazing technology is well represented by the De Havilland Comet, which has just flown tc Australia and back in thirteen and a quarter days, developing 460 h.p. with a weight ratio of i2lbs. per h.p. It therefore becomes interesting and perhaps useful to determine the extent to which metallurgy has contributed and is contributing.

It is proposed to confine this paper to Ferrous Metallurgy, since that is the field with which firstly the author feels most qualified to deal, and secondly, because steel, in a manner unparalleled amongst available metals, can be so profoundly modified in properties by changes in composition and heat treatment.

The problem of the maximum lift of airfoils has concerned the authors greatly since there were first discovered in the spring of 1932 serious discrepancies in this characteristic between results obtained in the wind tunnel of the Guggenheim Aeronautics Laboratory at the California Institute of Technology (GALCIT) and those reported from certain other wind tunnels. An elaborate experimental investigation by the junior author and A. L. Klein indicated that the value of CLmax for a given airfoil was strongly affected both by Reynolds number and by the degree of turbulence in the tunnel wind stream.