14 THE FLIGHT OF BIRDS. 
of a law. By experifhent he had discovered an 
indubitable principle, but subsequent experiments 
have discovered an equally indubitable fact, which 
at a certain point interferes with its operation. 
The angle cannot be reduced below, approximately, 
5° without bad results. At a less angle, with the 
necessary increase of pace, the friction of the plane 
against the air increases so rapidly that, so far from 
there being any gain from the further reduction 
of the inclination, there is an actual loss.* 
On this subject a writer in Flight has some very 
interesting calculations, founded partly, it is true, 
on theory, and requiring further verification by 
experiment, but probably representing the facts 
without any considerable deviation.t Indeed experi- 
ment has already proved his main thesis, so that 
it is only detail that requires further testing. He 
imagines aeroplanes having the ideal camber or 
curve for their planes, a large curve if they are to 
travel slowly at a great angle of inclination, a slight 
curve if they are to travel fast. They are to carry 
a weight of 100 lb. Let us imagine them driven by 
3 horse-power at the angles 30°, 25°, 20°, 15°, 10°, 5°. 
The velocity will increase rapidly as the angle is 
reduced. At 30° it will be 38 miles per hour. 
With the successive reductions of the angle it will 
increase to 47, 60, 78, 106, 134. The pace at 5° 
and even at 10° is greater than most people would 
wish to travel at, so the power applied might with 
advantage be reduced. Two horse-power at 10° 
*See The Aero Manual, p. 21; Flight, July 9, 1910; and 
Langley’s Aero-dynamics, p. 37. 
ft Loe. cit. 
