52 
PRINCIPLES OP GUNNERY. 
reference to the Table showing Results of Explosion, &c. (p. 48), that 
the explosion of 60 lbs. R.L.G. powder takes place in about J th of the 
time taken to explode 70 lbs. of P. powder under similar conditions. 
It will be seen from the diagram (Plate I.) that the pressure due to 
explosion increases very rapidly to a maximum, then at first it rapidly, 
and afterwards more gradually, decreases towards the muzzle; owing 
to the continually increasing space for expansion of the gas, caused by 
the continually increasing forward velocity of the projectile. 
Resistance The effect of the pressure in the bore is to overcome the resistance 
tion h ofT" to motion of the projectile, and to communicate velocity to the pro- 
FntiTbore jectile. The resistances to the motion of a projectile in the bore of a 
of a gun. g un must then be considered. 
They may be classified thus :— 
(1) The resistance to the motion of translation of the projectile. 
(2) The resistance to the motion of rotation of the projectile. 
(3) The frictional resistances of the studs and gas-check, opposing 
the motions of translation and rotation. 
Resistance The resistance to the motion of translation of the projectile depends 
motion of on its weight and the rate of increase of its velocity conjointly. Thus 
translation. 
R OC Wf' } 
where R denotes resistance, W weight of projectile,/the acceleration 
of the projectile* (or the rapidity with which velocity is communicated 
to it). The acceleration depends on the rapidity of explosion; and 
consequently the resistance to motion for the same weight of projectile 
would be greater in the case of ja quick-burning than with a slow- 
burning powder. This would intensify the pressure in the powder- 
chamber, as has been shown. 
A small difference in the weight of the projectiles, when a slow- 
burning powder is used, only increases slightly the maximum pressure 
in the bore. In experiments with a 12-in. gun of 38-tons, the Com¬ 
mittee on Explosives found that the effect of increasing the weight of 
the shot from 700 lbs. to 800 lbs., while firing the same charge of 
P. powder, did not appear sensibly to increase the maximum pressure 
in the bore.f Hence it becomes possible to fire very heavy projectiles 
without increasing inordinately the pressure in the gun, by the employ¬ 
ment of very slow-burning powder. 
Resistance The resistance to the motion of rotation of the projectile is only 
Sodon of a sma ^ per-centage of the resistance to the motion of translation, 
rotation. (Vide p. 40). This subject has been very fully discussed in the pages of 
“ Proceedings, R.A. Institution ” (Yol. VIII. p. 359), by Captain A, 
Noble, F.R.S., in a paper “ On the Pressure required to give Rotation 
to Rifled Projectiles.” Captain Noble states that in the 10-in. gun 
* The acceleration of the projectile in the bore (or the rate of increase of its velocity in a given 
time) is variable, owing to the variable pressure of the powder gas, and the varying resistances 
which are opposed to the motion of the projectile. 
f Vide “Report on the Experimental Rifled M.L. Gun of 38tons.” 
