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 
