Dynamic Meteorology IV (continued)

I found his lectures challenging and stimulating. I had often wondered about the influence of frictional forces on motion of the air, especially in low latitudes, and even had the temerity to make some of my ideas the subject of my first paper published in a scientific journal.

Lettau revealed the great complexity of the subject and made me question my simple assumption in that paper that the friction force in equations of motion could be a function of mean wind speed and altitude above ground level.

I retained little of the detail of Lettau's lectures for it had little relevance to the areas of meteorological research in which I was interested. But I enjoyed his lectures because of the immense breadth of his vision. One quotation made during his lectures made a profound impression. It was his enunciation of the principle of d'Alembert (1717–1783) which my notes record as "if it happens that a question which we wish to examine is too complicated to permit all elements enter into the analytical relation which we wish to set up, we separate the more inconvenient elements, we substitute for them other elements less troublesome, but also less real, and then we are surprised to arrive, notwithstanding our painful labour, at a result contradicted by nature".

It might be useful for the developers of computer models of the atmosphere to take note of that quotation.

Bureau of Meteorology