
794 The American Naturalist. [September 
resistance to such translation, speed of flight is determined by a 
force which may, for all practical purposes, be left wholly out 
of the account. 
5. “As a matter of fact,’ the statement that “it would be 
much easier to go slow than fast ” is a burlesque. 
6. Resistance of air at one mile or one hundred miles per hour 
is practically the same. 
So far as I can see, the paraphrased arguments of LeConte do 
not touch the problem of soaring flight in any way, but all the 
errors of the mechanical schools are evidently adopted by him. _ 
But here is by no means the end of this catena of difficulty. 
There are three ways, shown in the subjoined diagram, in 
which a surface and air can meet. 
1. Parallel to the surface. 
2. Obliquely to the surface. 
3. Normal to the surface. 

F: 
Sg ee 
The first meets with frictional resistance. 
The second with both friction and pressure. 
The third with pressure rcsistance only. 
The direction of the first and third resistance is in the line on 
which plane and air meet, there being a single stress on that line. 
The directions of the second resistances are both parallel, and 
normal to the plane, there being two stresses perpendicular to 
each other, and no stress on the line in which plane and air meet. 
It directly follows that direction of motion of the second case 
is a resultant, composed of two velocities, one on the line of fric- 
tional, the other on the line of pressure resistance, the plane 
being a body subject to two forces, neither of which are in the - 
line of motion. 





