GLIDING 13 



of support, of lift as opposed to drift. If Newton's 

 law held good, if the angle of inclination were more 

 and more reduced till it amounted only to, say, 5°, 

 then the resistance offered by the air would be too 

 small to be worth dividing up between lift and drift. 

 Even the lion's share would be worth next to 

 nothing. But experiment shows that an aeroplane 

 set at an angle of 5° can, if it travels fast, find 

 support in the air. 



But, although as we reduce the angle of inclina- 

 tion the resistance of the air does not diminish at 

 the rapid rate that Newton imagined, nevertheless 

 there must obviously be a point beyond which the 

 fining down of the angle cannot go, since the air 

 will at last cease to give the required support. 

 But before we reach the lowest possible limit another 

 factor comes in which checks us as we are making 

 successive reductions. As we continue to cut 

 down the angle there comes at last a point at which 

 the question of friction obtrudes itself in very 

 unpleasant fashion. Imagine the aeroplane driven 

 through the air at a very minute angle. If it is 

 to find support, it must travel at a very great pace, 

 else the resistance of the air will be too small. 

 With every diminution of the angle there must 

 be an increase of pace, and it might be thought 

 that, if only the pace were increased sufficiently 

 to make up for the diminution of the angle, all 

 would go well. Professor Langley made some 

 most valuable experiments which showed the great 

 advantage of a small angle of inclination, and, 

 emboldened by this great and important discovery, 

 he proceeded to frame a formula and to speak 



