172 SECTIONAL ADDRESSES 



why study these in a body of such appalling shape ? ' And the engineer 

 can only reply : ' Because I must. This shape was not evolved for its 

 intrinsic interest, but its strained form is important none the less — and 

 very difficult to calculate.' There you have the clash of interests : the 

 physicist wants his problems unalloyed, the engineer is not free to choose. 

 ' Go to the applied mathematician, thou sluggard ! ' is likely to be the 

 final word. 



Well, and suppose he does ? Will he find what he is seeking — a power 

 of analysis that turned on his problem will lead to its solution ? No : 

 he will find that mathematical analysis, developing in its own way, has 

 come to include a very beautiful technique for solving the general equa- 

 tions of elasticity, but the body in question must have one of a number 

 of shapes — among which his crankshaft is not included ! Again he is 

 sent away empty-handed, but now for a different reason. The applied 

 mathematician is not, as the physicist was, interested only in principles 

 (usually — -as was said by Sir Horace Lamb (1924) in writing of early 

 elasticians — it is a relief to him when he finally arrives at his differential 

 equations, and feels really at home) ; but he is interested in method, and 

 his zest of discovery is experienced in applying new methods, let their 

 limitations be what they must. 



10. So, as I see the matter, in this and countless other problems of 

 practical engineering — problems far too difficult for routine investiga- 

 tion — there will still be scope for academic engineers : they have a point 

 of view, and it is needed. In particular they possess a sense which the 

 modern ' high-brow ' mathematical physicist at times seems almost to 

 boast of having discarded : they can visualise — which is what is meant, 

 really, by this talk of ' nineteenth-century model-making '. Hard things 

 have been said in recent years about the Victorian physicist : one gathers 

 that his love of ' models ' was a vice which led him from the light, acquired 

 by debasing association with engineers. ' . . . When the physicist sought 

 an explanation of phenomena his ear was straining to catch the hum 

 of machinery '. Well, the work of nineteenth-century physicists is 

 still, I fancy, a fairly potent argument in their defence ; and I hope that 

 we engineers, working in fields that they explored, will avoid undue 

 humility in our answer to these taunts. I for one am defiant — and there- 

 fore perhaps impertinent ; but as a gesture of defiance I will maintain 

 that the tools of these mathematico-physical critics — theories of orbits, 

 elastic solids, fluids compressible and incompressible, wave motions — 

 were made for them by men who could visualise — ' model-makers ' — 

 and are applied by them now to problems which often they do not under- 

 stand or even seek to understand, relying instead on intermittent experi- 

 mental verification to show that they haven't yet gone wrong ! I think 

 it quite a sound line to follow in a fog, but I cannot see reason for so much 

 self-congratulation. ^ 



1 So H. Jeffreys in Nature, April 23, 1938 (p. 71S) : ' The modern quantum 

 theories have begun by direct and successful attempts to co-ordinate what we- 

 know, without attending to the details of any deeper interpretation, and as a 

 matter of method I think that their procedure is right. I should disagree, 

 however, with the elevation of the rejection of unobservables into a magic 

 philosophical principle.' 



