192 Major J. G. Barnard on Elongated Projectiles, 
haps I might add of Newton and Laplace; one of those problems — 
of mechanics to which the term difficult would be misappliel, — 
for analysis has never yet been able to grasp it at all. 
I have said that without the consideration of friction, the a 
; 
: 
tion upon the air of « rotating and non-rotating ball are iden — 
tically the same. But friction materially alters the character of 
this action. Whatever may be the immediate cause of this force 
—whether simply a collision of the inequalities of the surface 
with the particles of the fluid—or whether it is due to adhesion, 
the effect is that the moving surface puts in motion with i, the 
adjacent fluid particles, and in so doing, developes forces tan- 
gential and opposed to its own motion. 
Thus the anterior surface of the sphere(, 
revolving from F to D, and advancing from 
3 
F. uP 
D #p 
the point of view, and the sole one, in which 
Poisson has considered the effects of friction. pai 
But there is another effect which proves to be very powerfil 
Force cannot be applied to an elastic fluid, neither can motion 
imparted or destroyed, without effecting, at the same time, 
density and pressure. To retard a flowing current is to im 
its pressure; to accelerate it is to diminish the same. sala 
_ Applying this to the ball, the air, displaced and comp oak 
in front, escapes along the surfaces AF and AD. Near aa ot 
face, the action of friction is to retard the escaping curren 
of A to B, creates, at each point, forces, p, ? ip" 
; &c., tangential and opposed to its rotary mo 
Aas > tion, the resultant of which is a force acting 
pe 
from D towards F and tending to deflectthe — 
flight of the ball in that direction. This'8 f 
the side AF, and to accelerate them on the side AD, and 
consequence, an increase of pressure ensues on the ar 
and a diminution on the side AD; and therefore, a - 
pressure tending to deflect the 
from 
great circle ADF into four q 
4, 
A----3>—>E gles of 45° with the direction 
effects of friction, in the tw 
The posterior quadrant o p is in air so highly 
action is insensible or sera so.* On the side quadrant ™/ 
Tesultant of the forces of friction (the forces 7, p’; er x pe o 
are parallel (or nearly so) and opposed to the motion awa 
tion, : They have no effect (or but trifling) 0 ‘tion 10 
‘om its course, but acting upon the air, in dir 1 
* The high velocities of translation of military projectiles is | 
the 
lation A B, we may better ame oe a 
: ted them. aoe 
which I have ghee’ varified 7 i : 
ey ake ee 
ONE SSNS LE, Peer to erie ha eed ae hee a 
F towards D. If we divide rf : 
by the lines mo and 7p, on peor : 
