8 
On putting 
A = fx yR 2 , F=kR 3 
. 06 ) 
P = 
7 tR 2 V 2 
H and k being numerical coefficients ; hence 
,=i V 
A 7 T/xk 
~B ghp' 
(17) 
Prom the last formulae we conclude 
(1) For'similar projectiles the pitch at muzzle does not vary with 
the calibre. 
(2) With the increase of relative length of projectile the pitch rj 
decreases, since and h increase with the length. 
-D 
(3) With the same calibre, rj decreases with the decrease of weight of 
projectile and with the increase of air resistance, because here k 
decreases and p' increases. 
Having determined from (17) the pitch rj corresponding to a 
projectile of determined and length /, we get approximately the pitch 
rji for projectile of same weight and calibre, but of length li from the 
equation 
t=(!)* . <I8) 
This follows from (17), assuming that the moment of inertia B 
relatively to the equatorial axis is proportional to the square of length of 
projectile and the coefficient h to the length of projectile, but that p. 
does not change with the length. 
Calculations show that these suppositions approximately hold for 
projectiles of the present service form. 
VI. 
We will calculate from (17) the pitch at muzzle necessary for the 
steady flight of the 
(1) 11" cast iron shell of length 2*8 cals. ; 
(2) 8" steel fougasse shell of length P5 cals. ; 
(3) 6" steel fougasse shell, with cast iron head, of 3^ cals. 
Practice was carried on with these projectiles from guns of different 
twists at muzzle. The results show to what extent the formula is 
applicable to the solution of the problem. 
