SAILING BIRDS ARE DEPENDENT ON WAVE-POWER. 1 27 



steepest, and falling to zero at the crest. Let us suppose the 

 maximum velocity of uplift of the air to be about four feet per 

 second and the steepest part to be 10° slope. 



Now according to Prof. S. P. Langley, a plane surface 30" x 4-8", 

 weighing 1*1 lbs. will glide on air, without losing its elevation, at 

 a speed of 49*8 feet per second, if sloped 5°. That is, the plane 

 pushes 4*33 feet of air vertically downwards whilst it is translated 

 49 *8 feet in 1 sec. 



The same effect with regard to the position of the plane at the 

 end of its journey of one second's duration is produced if the plane 

 be sloped 5° downwards, and the air through which it passes be 

 pushed bodily upwards 4*33 feet in one second. 



Now the air over our wave is being lifted about four feet per 

 second ; so if the 1*1 lb. plane were launched with 5° downward 

 slope in the same direction the wave is travelling, from one foot 

 above the steepest part of the wave, it would overrun the wave 

 which has only a velocity of thirty feet per second. It would thus 

 get out of the air that is being lifted and shoot into the water in 

 the trough. But if the aspect of the plane be changed so that it 

 face 53° either to the right or left of the track of the wave, its 

 position above the mean sea level, and situation on the wave slope 

 will be unaltered : and, if the wave was of unlimited width the 

 plane would continue on its course till dashed ashore. 



The plane is simply abstracting the power stored in the wave 

 by a distant gale, and using it to counteract gravity. And if the 

 work be continued long enough, or a multitude of planes be con- 

 tinually drawing on the reservoir of power, the wave must 

 inevitably be flattened. 



The velocity of 49-8 feet per second is sufficient to raise the plane 

 to an elevation of thirty-eight feet in one and a half seconds, if its 

 course be changed from horizontal to vertical, it there comes to 

 rest. And from a poise at this station the plane may swoop down, 

 at great disadvantage if close to the back of the wave, at various 

 slopes and directions till it cuts into the air that is being raised 



