However, since strength is a function of material and form rather than weight, it is possible by selecting proper materials and adopting suitable structural forms to evade to a certain extent this “law of the cube.” The whole history of structural science has therefore been a series of attempts to find stronger and lighter material and to discover methods of so modifying form as to dispense with all parts of a structure that do not contribute to its strength. So in aerodromics the structural problem has been that of finding materials and forms best suited to the purpose for which they are required, for it does not always follow that either the form or the material best suited for one scale of construction is the most advantageous to employ on a different scale. Nor is even the form or material which gives the greatest strength for the least weight necessarily the best to employ. For the structural problem must necessarily be co-ordinated with those of balancing, propelling, and transporting, and each must, therefore, have its proper attention in the design of the whole machine. Many of the general considerations of the design of an aerodrome sufficiently large to transport a man were determined during the spring and summer of 1898, when the first actual drawings (Plate 32, Figs. 1, 2 and 3) of the proposed machine were made. Starting with the assumption that the Models Nos. 5 and 6 were capable of transporting a load of approximately ten pounds more than their weight, it was seen that, since the supporting surface of any aerodrome would increase approximately as the square of the linear dimensions, in order to carry a man the aerodrome would need to be approximately four times the linear dimensions of these models. Calculations based on the results accomplished in the construction of the models indicated that such an aerodrome would need to be equipped with engines developing 24 horse-power. The best that could reasonably be hoped for was that these engines would not weigh over 200 pounds, and, therefore, allowing 40 pounds for fuel and fuel tanks, it became necessary to bring the weight of frame, supporting surfaces, tail, rudder, propellers and every other accessory within 250 pounds, if the total weight of the machine, including 150 pounds for the aeronaut, was not to exceed 640 pounds, or 16 times the combined weight of the model and its load of 10 pounds. Although the problem of constructing the frame, wings and all other parts within the limit of 250 pounds seemed indeed formidable, it was believed that the greatest obstacle in the production of such a machine would be that of securing a sufficiently light and powerful engine to propel it. [Illustration: PL. 32 DRAWINGS OF PROPOSED MAN-CARRYING AERODROME, 1898] [p131]