Professor Glazebrook’s Excuse

R. V. Southwell, from the NPL, opened the discussion after the talks and sought to defuse the situation with good-natured praise for all of the speak­ers. Southwell wondered if the Stokes equations were quite as secure as Bair – stow assumed. He raised the possibility that the underlying physics might in­volve even more complications than those already expressed in the equations. He also reported that wind-tunnel experiments under way at the NPL seemed to be finding a value for the circulation around a wing that was similar to that predicted by Prandtl, though he, Southwell, doubted if the flow near the wing would correspond to that assumed by the circulatory theory. On the other hand, he was enthusiastic about Bairstow’s fundamental research program and fully supported the need to explain the success of Prandtl’s ap­proach. Bairstow’s own contribution to the discussion was a bland response to a Dutch speaker from the audience who had sketched some of the recent work at Aachen and Gottingen. Bairstow said he was glad to hear that Con­tinental workers were taking viscosity seriously. The discussion ended on a bizarre note when Sir George Greenhill proceeded to inform the audience that the modern approach to aerodynamics was based on a paper that Ray­leigh had written fifty years ago on the irregular flight of the tennis ball. This intervention was remarkable for two reasons. First, Greenhill was rewriting history and was expecting his audience to have forgotten all about the discon­tinuity theory of lift and his own, and Rayleigh’s, contribution to it. Second, it is unclear whether Greenhill had come into the lecture late or whether he had failed to register what had been said in his presence. Glazebrook had to draw Greenhill’s attention to the fact that he was repeating a version of what Major Low had just said. This done, Glazebrook thanked all of the speakers and promptly declared the meeting closed.

Despite the pointed criticism of the Advisory Committee, Glazebrook had chosen not to respond to Low. He might have been distracted by Greenhill’s odd behavior but, leaving psychology aside, there is another possible explana­tion for Glazebrook’s nonresponse. The Wednesday session was not the first time the issue of Lanchester had been raised at the Congress. Low and Glaze­brook had crossed swords on the previous Monday, June 25. It is possible that Glazebrook had decided he had said all he was prepared to say and was not going to be drawn out on the subject again. On that Monday, Glazebrook had given a paper titled “Standardisation of Methods of Research.”104 In the

discussion that followed he had encountered some criticism by Major Low about the reliability of wind-tunnel results. Low cited some negative remarks from G. P. Thomson’s book on aerodynamics and argued that wind-tunnel data needed to be corrected. The “Lanchester-Prandtl theory,” said Low, had shown how to make the corrections, and this theory would soon be the sub­ject of his own talk. Glazebrook, who did not like to air the problems of wind – tunnel research in public, suggested that Prof. Thomson had surely changed his mind. Then, perhaps alerted by Low’s mention of his forthcoming talk, Glazebrook added a comment that was not a direct response to anything that had actually been said. As if to head off trouble, Glazebrook launched into an apologia for the way Lanchester had been treated: “With regard to the refer­ence to the Prandtl theory, I trust there is no one here who will in any way depreciate the enormous value of the work done by Mr. Lanchester and of the suggestions he has made. But it was not until Prandtl put some such sugges­tions into mathematical form that it was possible to attach to them the kind of value they have now gained, or to give Mr. Lanchester all the credit and praise that we should desire to give for his work” (65). This preemptive state­ment may explain why, on the following Wednesday, Glazebrook remained silent. He had no wish to go round the issue again.

Glazebrook’s desire to give due, if belated, credit to Lanchester may be accepted at its face value, but as an excuse for the neglect of the circulation theory, his claim has three, obvious weaknesses. (1) To say that we can now see that Lanchester was doing something valuable because Prandtl has made it clear to us does not explain why the British could not have worked it out for themselves. (2) In reality, as I have argued, British mathematicians had no difficulty in seeing the underlying mathematical form of Lanchester’s ideas. It was not the obscurity of the relation to mathematics that was the cause of the trouble, but the opposite. British experts such a G. I. Taylor were very familiar with the mathematical form of the circulation theory. It was actually the underlying mathematical form (the potential flow of an inviscid fluid) that they rejected on the grounds that it could not refer to processes that were physically real. (3) When British mathematicians were presented with a developed mathematical expression of Lanchester’s theory, they still expe­rienced difficulty in coming to terms with it—witness, for example, G. H. Bryan’s negative review of Joukowsky, the responses of Lamb to Kutta, and Bairstow’s response to Prandtl and Betz. In all cases the work struck them as a problem rather than a solution. None of these three points is accounted for by Glazebrook’s version of the events. It is not difficult to see why a well – informed practical designer such as Low might have felt less than convinced by Glazebrook’s answer. No wonder he could not resist raising the matter again and putting Glazebrook on the spot.105

I have now looked at some of the discussions about aerodynamics that took place in Britain in the immediate postwar years. It is clear that the math­ematically sophisticated British experts did not take the view that “there was nothing to learn from the Hun.” They were learning and learning quickly, but there was disagreement about what, and how much, was to be learned. How, and on what terms, was the Gottingen work to be assimilated? While the arguments at the Royal Aeronautical Society and the International Con­gress were conducted in the public realm, there had been other arguments that were still running their parallel course behind the closed doors of com­mittee rooms. It is to these that I now return. In the next chapter I pick up the story of the discussions initiated in the Aeronautical Research Committee by Glauert’s resolve to champion the merits of the circulation theory and Prandtl’s theory of the finite wing.