The Compressed Air Wind Tunnel has now been in more or less regular use fpr a little over a year, during which time some interesting results have been accumulated. While these results are not yet by any means complete enough to enable an exhaustive study of scale effect to be made, they are nevertheless of sufficient extent to throw light on several points in respect to scale effect which have hitherto been somewhat obscure, and in particular to show more clearly the relative effects of scale and turbulence on the important phenomenon of the maximum lift of aerofoils.

It may be well to review briefly the history of the development of the Compressed Air Tunnel and to give a very short account of the construction of the tunnel at the N.P.L. and of the preliminary work associated with its special measuring apparatus, as no mention of these matters has yet been made in the Society's publications

The object of production is to give service to the user. The value of that service is generally measured by the results obtained (either by way of performance, ease of maintenance, reliability, long life, and appearance) against the cost; and given two similar products, by which I mean products designed to fulfil identical functions, the purchaser will prefer the one which gives him equivalent or greater service at the lesser cost.