AN ELONGATED PROJECTILE. 
589 
and 
Therefore 
therefore 
therefore 
n* — 
4 x 
211 
171 
17 
5 
A 
25 
X (a — y) 
2117T 2 
5 X 171 X 17 X — X (a — y) 
<T 
log21l7r 2 = 3*3185843, 
log 5 = 0*6989700, 
log 171 = 2*2329961, 
log 17 = 1*2304489, 
log - = 4*3831655, 
° a 
1*8910968. 
' 7) ~ 0*4366773 ; 
lo g» 2 = 2*8819070, 
log n = 1*4409535; 
n = 27*603. 
Consequently, even for double shell, the twist in the 6*3-in. and the 
8-in. howitzers—one turn in sixteen calibres—seems excessive; the 
spin imparted being theoretically far in excess of what is required for 
stability, the only effect of the excess of spin being to diminish the 
drift, which increases as the angular velocity diminishes. 
When the shell is filled the stability is slightly increased, and the 
spin need not be so great. For suppose a common shell, filled with 
powder of density 1*6 ; then, since a and y depend only on the external 
shape of the shell, they have the same values as before, and 
a — y = *68184. 
p _weight of the displaced air 
<t weight of the shell 
4 2 
8 c 
X 
1 
816 
| (l - p) x 7-207 + | 7 T*e g x 1-6 
27 
(19 x 7*207 + 8 x 1*6) 816 
27 
149*733. X 816’ 
But 
