Look at the way the Japanese have painted birds... . The system is simple. They have sat down in the countryside and have for a long time watched the birds in their flight. By dint of watching them they have ended by understanding their movements.

Auguste Renoir

The wing of a bird in flight has no fixed shape. Its shape is constantly changing in response to the constantly changing pressures of the air through which it moves, or to suit changes in course or speed. Man has never invented anything at once so strong and so delicate, anything so sensitive in its adjustment to the continuously varying conditions it has to meet.