AERONAUTICAL PROBLEMS OF THE 
PAST AND OF THE FUTURE.’ 
BY 
R. V. SOUTHWELL, F.R.S. 
PART I. 
The Scope of Aeronautics. 
1. Twenty years ago, a man might hope to traverse the whole field 
of Aeronautics in the space of an hour’s discourse: to-day, that hope would 
be as vain as the design of Comte and Herbert Spencer, to take all know- 
ledge for their province. Growing at an amazing rate, under the stimulus 
of war, Aeronautics has drawn for its sustenance on many sciences and arts : 
on metallurgy and textile science, for its materials of construction; on 
thermodynamics and mechanical engineering, for its engines of amazing 
power; on structural engineering, for designs in which every ounce of 
unnecessary weight must be eliminated, and the margin of permissible 
uncertainty is smaller than ever before; on nayal architecture, for hulls 
which enable its flying boats to skim the surface of the sea at speeds 
sufficient for their air-borne flight ; on meteorology, for knowledge of the 
conditions with which it has to reckon in its struggle against the forces of 
Nature. On each and all of these sciences it has made demands more 
stringent than any that they had encountered before ; on each it has left, 
as it were, the impress of its own personality,—the trace of enquiry aimed 
at some particular goal. No one man can pretend to knowledge pervading 
all these subjects,—certainly not I; nor, if I did, could I hope to review 
them even cursorily in the time available to me this evening. 
Aerodynamics,—the Science of Bodies in Motion through a Fluid. 
2. But given all these sciences, Aeronautics has to graft on to them 
another, which is Aerodynamics,—the science of bodies in motion through a 
fluid by which they are totally submerged; and this science Aeronautics 
has so largely dominated that it may almost claim it as its own. But for 
that fact, there would be little justification for the use of the term Aero- 
dynamics ; for it is seldom necessary to take account of the air’s compres- 
sibility, and in the main our results would apply equally well to bodies 
moving through water. Visitors at times seem surprised to find us testing 
torpedoes or paravanes in our wind tunnels: the explanation is, that 
although air 7s elastic (so that many strokes of the pump are required to 
inflate a motor tyre), yet in its flow past bodies moving at any ordinary 
speed it undergoes such slight changes of pressure that the corresponding 
changes in density may be neglected. 
The torpedo is older than the aeroplane, and its problems, similar in 
kind, were encountered earlier than those of artificial flight. Nor was it 
1 Evening Discourse to the British Association, Southampton, August 28, 1925. 
