792 The American Naturalist. [September, 
lel wires, to preserve stability ; otherwise, the experimental plane 
would slip down the air plane. 
It follows that atmospheric resistance is a purely static feature 
in all cases; as completely so as a rigid inclined plane, resolving 
all forces impinging upon it. This becomes still more evident 
when we see that it is the experimental plane that determines the 
direction of air resistance, and not the direction in which plane 
and air meet. If air moved vertically upwards, or from the rear, 
or from any other direction, against the lower surface, the direction | 
of resistance would be unchanged, and the experiment equally : | 
| 
: 

Er A a TN 
effective. It was not to employ horizontal wind that the experi- 
ment was arranged, but to parallel the case with a soaring bird, 
the working force of which is gravity. 
Magnitude of resistance would vary, with the same wind, as E . 
its direction approached or receded from the normal line, but, as , 
will be shown farther on, magnitude is unimportant, direction 
being the vital matter. 
If the experimental plane were supposed to be of the same 
specific gravity as the air it displaces, and some other force used 
to hold the plane against, or drive it upon air, the same result a 
would follow. This force would be resolved, as gravity is resolved, 
by the air plane. 
The enormous error of the mechanical schools in estimating 
resistance of air to oblique surfaces is now conspicuous. This 
error has the sanction of the great name of Newton, and stands 
squarely across the pathway leading to artificial air navigation, 
setting up scarecrows along every avenue to success. 
But it is consoling to know that no man, not even a Newton, 
can diagram a force into nature that was not there before the 
diagram was made. 
The entire nature of air resistance is misconceived. The case 
is a curious one of ġouleversement, The activities are turned 
upside down. Instead of the surface resolving the resistance, it 
is the resistance that resolves whatever forces drive the surface 
upon it. I have examined over a hundred text-books of 
mechanical teaching, and have found no exception to the preva- 
lence of this error. They all get resistance on the line in which 
se oy 
Pri tee ee aT Nees othe SE 
EST 
ae 
3 S EREA 
EENES EEPE ASEE EE S al RP N E S 

EAE A aS 



