The Aerofoil & The Screw Propeller, two papers by Frederick Lanchester, 1915 edition as delivered to Institution of Automobile Engineers.
Lanchester began to study aeronautics seriously in 1892, 11 years before the first successful powered flight. Whilst crossing the Atlantic, he studied the flight of herring gulls: seeing how they were able to use motionless wings to catch up-currents of air. He measured various birds to see how the centre of gravity compared with the centre of support. As a result of his deliberations, Lanchester eventually formulated his circulation theory of flight.