x PRACTICAL PURPOSE 291 



an aeroplane designed by him without any definite 

 knowledge of what the Wrights had done. Since that 

 period, the advance of dynamic flight has been rapid 

 and marvellous ; and aeroplanes of various types are 

 now in everyday use, particularly for military purposes. 



The performances of the earlier machines depended 

 very largely upon the pilots, who had to give close 

 attention to different controls in order to keep the planes 

 in a condition of stability in the air. The problem of 

 producing a machine which is automatically steady in 

 free flight is largely mathematical ; and it involves the 

 theory of small oscillations about a state of steady 

 motion developed by Lagrange, Kelvin, Routh and 

 other men of science. Definite attention has been given 

 to the mathematical conditions which have to be satisfied, 

 in order to solve the problem of inherent stability, by 

 G. H. Bryan and F. W. Lanchester ; and their con- 

 clusions, with the results of experimental research on 

 models at the National Physical Laboratory, largely by 

 L. Bairstow, have led to the construction of the B.E. 

 biplane, which is almost independent of the pilot except 

 when near the ground, where personal control must 

 be exercised. 



The forms of early aeroplanes were determined chiefly 

 by trial-and- error methods ; and little inducement was 

 given to scientific men to devote themselves to the 

 experimental and theoretical studies by which the most 

 efficient types of machine can be secured. Work in 

 the laboratory and calculation in the study must, how- 

 ever, eventually determine the lines upon which a 

 flying machine can be designed that may be launched 

 into the air with as much confidence in its safety and 

 inherent stability as a vessel can be trusted to leave 

 the slips of the dockyard in which it has been built. 



