In Prof. Langley’s lifetime, we had many discussions regarding the width and shape of aeroplanes. The Professor had made many experiments with very small and narrow planes, and was extremely anxious to obtain some data regarding the effect that would be produced by making the planes of greater width. He admitted that by putting some two or three aeroplanes tandem, and all at the same angle, the front aeroplane _a_ (Fig. 57), would lift a great deal more than _b_, and that _c_, would lift still less. He suggested the arrangement shown at _a′_, _b′_, _c′_, in which _b′_ is set at such an angle as to give as much additional acceleration to the air as it had received in the first instance by passing under _a′_, and that _c′_, should also increase the acceleration to the same extent. With this arrangement, the lifting effect of the three aeroplanes ought to be the same, but I did not agree with this theory. It seemed to me that it would only be true if it dealt with the volume of air represented between _j_, and _k_, and that he did not take into consideration the mass of air between _k_, and _l_, that had to be dealt with, and which would certainly have some effect in buoying up the stream of air, _j_, _k_. Prof. Langley admitted the truth of this, and said that nothing but experiment would demonstrate what the real facts were. But it was a matter which I had to deal with. I did not like the arrangement _a′_, _b′_, _c′_, as the angle was so sharp, especially at _c′_, that a very large screw thrust would be necessary. I therefore made a compromise on this system which is shown at _a′′_, _b′′_, _c′′_. In this case _a′′_, has an inclination of 1 in 10, _b′′_ an inclination of 1 in 6, and _c′′_ an inclination of 1 in 5. It will be seen that this form, which is shown as one aeroplane at _a′′′_, _b′′′_, _c′′′_, is a very good shape. It is laid out by first drawing the line _c_, _d_, dropping the perpendicular equal to one-tenth of the distance between _c_ and _d_, and then drawing a straight line from _c_, through _e_, to _f_, where another perpendicular is dropped, and half the distance between _d_ and _e_ laid off, and another straight line drawn from _e_, through _g_, to _h_, and the perpendicular _h_, _i_, laid off the same as _f_, _g_. We then have four points, and by drawing a curve through these, we obtain the shape of the aeroplane shown above, which is an exceedingly good one. This shape, however, is only suitable for velocities, up to 40 miles per hour; at higher velocities, the curvature would be correspondingly reduced. [Illustration: Fig. 57.--Diagram showing the evolution of a wide aeroplane.] THE ACTION OF AEROPLANES AND THE POWER REQUIRED EXPRESSED IN THE SIMPLEST TERMS.