10 
Assuming the air resistance proportional to square of velocity, 
h = 12*74. 
P ' = 0*0394. 
With these data, formula (17) gives 
^ = 25-1 
(this is near 77 = 24*7 of the above table, l being 4’5). 
In shooting from an 8 " mortar with a pitch of 35 cals, the accuracy of 
4-5 cals, projectiles was unsatisfactory, although satisfactory when fired 
from the 8 " and 9" light mortars with a pitch of 15 cals. 
The projectiles fired from the 8 " light experimental gun with a pitch 
of 25 cals, were ordinarily steady in flight, however, solitary unsteady 
ones were observed. We must conclude that a pitch of 25 cals, is the 
extreme limit for a projectile of 4’5 cals. This follows from (17). 
To guarantee a satisfactory accuracy from the 8 " light guns, the pitch 
should be 20 cals. 
(3) For the 6 " fougasse steel shell, with cast iron head, of 3J cals, 
designed by General Engelhard, 
P = 33-28 kilos (81*25 Russian pounds), 
It = 0*0762 m., 
log h = 4-8761, 
~ = 6-874, 
/x = 0*606. 
Assuming the air resistance proportional to square of velocity, we 
shall find 
h = 8-96, 
fp' = 0-0394; 
with these data 77 = 38 - 5 .* 
When fired from a 6" gun 1.90-pr., (Russian) of the 1877 model, with 
a pitch of 45 cals., projectiles of 3Jcals., designed by General Engelhard, 
were very unsteady, but from the 6" gun 120-pr. (Russian), with a 
pitch of 25 cals., the accuracy was satisfactory. 
VII. 
Hence, for steady flight of a projectile of the given design, the pitch 
must not exceed a certain limit, which, evidently, is got from (17). 
The shearing strength of driving bands ordinarily limits the least 
pitch. 
There are sufficient experiments showing that decrease of pitch at the 
limits met with in practice does not influence sensibly the accuracy. 
For example, from the 9" mortar, with pitches of 40, 35, and 20 cals., 
* Assuming for initial date 77 = 50*4 and 1= 2*8, from (18) we find 77 = 38*8 for shell of 
3J calibres. 
