“The Whimsical Condition of Mankind”

In my study of the difference between the British and German responses to the circulatory theory of lift I have followed out the implications of Frank’s comparison. I have tried to dig into what he called “the depths,” where, as he rightly said, “the real battle for the progress of knowledge has been fought.”112 I have engaged with the details of the scientific and technical argumentation over the theory of lift because it is here, in these details, that both the social character of knowledge and the consequent relativity of knowledge find their most revealing expression. The story reminds us of the sheer contingency and unpredictability of the outcome of any research enterprise and shows how complex and fine-grained that contingency can be. It shows the vital and ineradicable role played by cultural traditions and the institutions that transmit these traditions. And, as Frank predicted, nowhere in the analysis of scientific discourse was a legitimate place found for the term “absolute truth.”

This insight is in constant danger of being forgotten or obscured by the false friends of science. The relativity of all scientific concepts to culture and society is deemed unacceptable by the self-appointed guardians of knowledge who claim to “take reflective responsibility, as it were, for the normativity of our most fundamental cognitive categories.”113 Historians and sociologists, like experimental psychologists and anthropologists, have always known that it is not normative posturing but close and careful empirical studies of cogni­tion that are needed. Strange though it may seem, this principle needs special emphasis when the cognition in question is that of scientists and engineers. The practices of scientists and engineers must be studied in a hard, factual light as natural phenomena that belong to the material world of cause and effect. Only studies conducted in this spirit can carry the analysis beyond ide­ology and propaganda and lay the basis for a proper, public understanding of science and technology.114

Detailed empirical studies always need a methodological context, and at­tention must always be given to the broader framework in which they are un­derstood. Thus one may legitimately ask where all the intellectually brilliant activity of the men and women I have studied is to be positioned in relation to the grand philosophical categories of Progress, Reality, and Truth. Now that the facts of the case study are at hand, the answers are not difficult to supply, though their implications may be disturbing.

Let me take each category in turn. That the work of the German engineers constituted technical progress is beyond doubt, and it is this which eventually had its impact on the British. The German work had utility and practicality relative to goals and interests shared by the experts of the two nations. The British led the way in the study of stability, but when it came to the study of lift and drag, failure and frustration took its toll on the British experts. The practical rewards and opportunities offered by the German approach eventu­ally tempted even the strictest to compromise their principled commitment to theories with a firm basis in physical reality. The theory of circulation and Prandtl’s theory of the finite wing allowed the experts to do things that they wanted to do, and that fact alone was, in its own way, rewarding. If the at­traction of moving forward could not rationally compel a change of mind on important theoretical questions, it encouraged a pragmatic accommodation.

That everyone in the field of aerodynamics, British and German, was, each in his or her own way, grappling with reality is also evident, and this was wholly taken for granted in all of the reasoning of the actors I have described. Although one may question the extent of Sir George Greenhill’s connection with reality in his notorious Reports and Memoranda No. 19, on discontinu­ous flow and free streamlines, this work did not set the pattern for the future reports of the Advisory Committee. As a group the British were no less con­cerned than their German counterparts with understanding the real perfor­mance of real airplanes under real conditions of use. And wasn’t Sir George himself acting as the spokesman of the practical realists when he (correctly) took G. H. Bryan to task for neglecting the gyroscopic effect of the engine and propeller in his analysis of stability?

Engagement with reality may be common ground, but my example shows that there are different ways of grappling with reality. It also shows that these different modes of engagement are social modes belonging to, and sustained by, different groups with different local traditions. Such differences can di­vide groups that otherwise share much by way of a common culture, as did the British and German experts in aerodynamics. Even more important, the example shows that there are no independent methodological principles by which these different forms of engagement could be reliably and usefully as­sessed. Such principles as emerged in the episode were themselves integral to the forms of engagement they were used to justify. They were rationalizations of existing practices and institutions. That there are different ways of engag­ing with the world may seem obvious; that the only ground available to the actors for justifying their choices is question begging is perhaps less obvious. But obvious or not, it follows directly from the fundamentally social charac­ter of cognition. This is one reason, though not the only reason, why the so­ciologically minded David Hume was right when he said that all the sciences have a relation to human nature and that “however wide any of them may seem to run from it, they still return back by one passage or another.”115

What, finally, is to be said about truth? The progress in aerodynamics made in the technische Hochschulen and the University of Gottingen derived from the use of a theory of perfect fluids in potential motion. The theory dealt with an idealization and a simplification. This theory was dismissed in Cambridge and London as physically false and logically self-defeating. It was false because it denied the viscosity of the air and self-defeating because cir­culation was unchanging with respect to time, and its origin was beyond the reach of the theory. The premises of the British objections were true and the reasoning based on them was sound, but the conclusions led to failure rather than success.

The German advances in the understanding of lift and the properties of wings depended on the use of abstract and unreal concepts that were some­times employed with questionable logic. Progress in aerodynamics thus de­pended on the triumph of falsity over truth. Everyone knows that false prem­ises can sometimes lead to true conclusions and that evidence can sometimes support false theories, but the story of the aerofoil involved more than this. The successful strategy involved the deliberate use of known falsehoods poised in artful balance with accepted truths. The supporters of the theory of circulation showed how simple falsehoods could yield dependable conclu­sions when dealing with a complex and otherwise intractable reality. This is the real enigma of the aerofoil.

The enigma would hold no surprises for Hume. It would simply be an expression of what he called “the whimsical condition of mankind.”116 The lesson Hume learned from the study of history and society was that “the ul­timate springs and principles” of the natural world will never be accessible to the human mind. The utmost that reason can achieve is the simplifica­tion of complexity. Humans live and operate in a world of limited experience dominated, necessarily but beneficially, by custom, convention, habit, and utility. Hume acknowledged that “the philosophical truth of any proposi­tion by no means depends on its tendency to promote society” but argued that we should be neither surprised nor unduly alarmed if truths (or sup­posed truths) that lack utility sometimes “yield to errors which are salutary and advantageous” (279). The story I have told deals with a technology that may seem remote from the world whose problems exercised Hume, but the central fact to emerge in my story, the fact I have called the real enigma of the aerofoil, can be understood in the humane, skeptical, and sophisticated terms he offered. Among the British it was an accepted truth that the air was a viscous fluid governed by Stokes’ equations. In the field of aeronautics that truth, if truth it be, yielded to the erroneous but salutary and advantageous picture of the air as an inviscid fluid governed by Euler’s equations.

Are there general lessons to be learned? Not if aerodynamics is a special case, but I do not think it is a special case. The conclusions reached in this case study surely can be generalized.117 What, then, should be concluded? Individual developments in the sciences will differ in their details, but what Frank had to tell us about the compromises involved in the design of air­planes applies (and was meant to apply) to the technology and instruments of all thinking. There are always compromises to be made. The warning given by von Mises against the phantom of absolute cognition will always be rel­evant. And there will always be a role in science and engineering for the blunt advocacy of a Major Low and the rapier responses of a G. I. Taylor. Above all, what Kuchemann had to say about the idealizations of aerodynamics cap­tured the essence of the creative work of Lanchester, Prandtl, and Glauert. But idealizations are salutary and advantageous falsehoods which play a vital role in all science, pure as well as applied. In stressing the role of idealization,

Kuchemann may have identified a feature of cognition that is more salient in engineering than in physics—but it is the engine of progress in all fields. Those who point to the airplane as a symbol of the truth of science, the power of technology, and the reality of knowledge are therefore right—but do they know what they are saying? The enigma of the aerofoil is the enigma of all knowledge.