The mathematical equation relating to the lift and drift of a well-made aeroplane is extremely simple; at any practicable angle from 1 in 20 to 1 in 5, the lifting effect will be just as much greater than the drift, as the width of the plane is greater than the elevation of the front edge above the horizontal--that is, if we set an aeroplane at an angle of 1 in 10, and employ 1 lb. pressure for pushing this aeroplane forward, the aeroplane will lift 10 lbs. If we change the angle to 1 in 16, the lift will be 16 times as great as the drift. It is quite true that as the front edge of the aeroplane is raised, its projected horizontal area is reduced--that is, if we consider the width of the aeroplane as a radius, the elevation of the front edge will reduce its projected horizontal area just in the proportion that the versed sine is increased. For instance, suppose the sine of the angle to be one-sixth of the radius, giving, of course, to the aeroplane an inclination of 1 in 6, which is the sharpest practical angle, this only reduces the projected area about 2 per cent., while the lower and more practical angles are reduced considerably less than 1 per cent. It will, therefore, be seen that this factor is so small that it may not be considered at all in practical flight. [Illustration: Fig. 1.--Diagram showing the reduction of the projected horizontal area of aeroplanes due to raising the front edge above the horizontal--_a_, _b_, shows an angle of 1 in 4, which is the highest angle that will ever be used in a flying machine, and this only reduces the projected area about 2 per cent. The line _c_ _b_ shows an angle of 1 in 8, and this only reduces the projected area an infinitesimal amount. As the angle of inclination is increased, the projected area becomes less as the versed sine _f_ _d_ becomes greater.]