Since the commencement of commercial aerial transport very great results have been obtained in certain directions. In the first place, the mere fact of flying has been reduced from a great adventure to a commonplace method of travelling. In this respect it is interesting to notice, on Croydon terminal aerodrome, the very great variety in the classes and types of people travelling by air. Men and women, old and young, daring and nervous, calm and fussy, clergymen, commercial magnates, school children and nurses, babies and helpless invalids, and in fact every sort of persons that you will find on a railway, travel regularly and peacefully by air. And it is certain that a very large proportion of these persons would have told you four years ago that they would not go in an aeroplane for anything.

In presenting this paper the authors are conscious of the fact that it contains very little information which is actually new. They feel, however, that the collection and co-relation of items of theory and experience which may not be widely known will prove useful to those who may have to consider the employment of airships on long journeys through necessarily varying meteorological conditions.

Although the static air-cooled radial engine is by no means an innovation irr the history of aero-engine development, its career has been somewhat chequered. Some ten years ago several practical comparatively low-powered air-cooled radials were produced and successfully flown, but they were ousted by the rotary engine on the score of power/weight ratio.

When in 1917 it was found that the limit of the air-cooled rotary had been reached, a demand arose for an engine of the same characteristics of manoeuvrability, compactness and light weight as this type, but of much higher power, and with a general all-round performance and fuel consumption comparable with the water-cooled engine of that date.