The more I think about the subject chosen for this Address, the rasher does it seem. To proclaim limits to human flight is to do two things. To say what can be done, and to suggest what cannot. Now, though there may be little rashness in the one, there is much in the other. If I say that such and such a thing can be done and someone in the distant years points out that actually it has not been done, my shade has the easy reply that achievement requires effort and that my critics should use their brains.

But if I suggest that certain boundaries cannot be crossed, what fun for the coming race of engineers who cross them (if they do), than to poke fun at the memory of your lecturer to-night! And when I use the word flight I mean flying with wings and not the flight of a projectile.

When I received the invitation to deliver this Memorial Lecture, and “Turbulence” was chosen as the subject, I remembered that my good friend, G. I. Taylor, gave a very stimulating talk on the same subject ten years ago. It was his G. I. Symons Memorial Lecture before the Royal Meteorological Society. He succeeded in fulfilling his job without using one mathematical symbol, the President of the Society, Sir Gilbert Walker, insisting very definitely that “turbulence without tears” was what he wanted. I do not think that I can duplicate Taylor's achievement completely; however, I shall try to reduce the mathematics to a minimum.

Simplified method of solution of the equation,

1

• where p = the permissible stress.

• py = proof stress.

• d = external diameter of strut.

• k = radius of gyration.

• l = length of strut.

• δ = eccentricity.

• E = Young's modulus of elasticity.

This method is mainly developed in order to reduce the time taken to work out a series of curves of permissible stress against (l/k). The graphical methods have so far been elaborate and no definite accuracy can be maintained.