38 
PRINCIPLES OE GUNNERY. 
of 16-pr. = 1358 f.s., calibre 3*6 ins., twist 1 turn in 30 calibres. 
From (2), 
number of revolutions per second — — = 150-9 ; 
108 
and from (3), 
angular velocity = 2 tt X 150*9 = 301*87t = 918-1. 
Also, linear velocity of rotation of a point on the surface of the pro¬ 
jectile is 
948*1 x 1*77 = 1678*2ins. per second, 
since diameter of shell is 3*54 ins.; or, expressing the velocity in feet 
per second, the linear velocity of rotation of the 16-pr. shell 
__ 1^7 8 2 _ ^ 39.3 p er second. 
I d 
Wort. Work .—When a projectile has been set in motion from rest, some 
force or pressure must have been exerted upon it. This force or pres¬ 
sure is then said to have done work; and the amount of work done 
is measured by the product of the pressure into the distance through 
which the projectile has been moved. Work done is usually ex¬ 
pressed in foot lbs., although for artillery purposes it is often expressed 
in foot tons. 
Thus, if T be the pressure in lbs. exerted on a projectile through the 
space of 8 feet, then the work done on the projectile is 
po 
P X 8 ft. lbs. = ft. tons. 
But, in practice, the pressure exerted on a projectile during its 
passage through the bore of a gun is not constant but variable; so that 
to obtain the approximate amount of work done, the product of the 
mean pressure on the projectile into its distance moved through the bore 
of the gun must be taken. Then 
P = mean pressure on projectile 
= mean pressure on the bore of the gun. 
A _6 
EE5 > I I 
AB =S 
Example.— If the total mean pressure on the base of a Palliser shell, 
fired with a battering charge out of the 10 -in. M.L. gun, were 516 tons, 
what would be the work done on the shell at the muzzle ? 
The distance through which the pressure acts must be the difference 
between the length of the bore and the length of the cartridge. 
Length of bore of 10-in. M.L. gun is 145*5 ins. 
Mean length of cartridge. „ 25"5 „ 
The difference will be the distance passed over by the shell from its 
seat to the muzzle—viz., 120 ins. = 10 ft.; consequently, work done 
= 10 x 516 = 5160 ft. tons. 
Pressure 
mcVoiithe It is often convenient to express the pressure exerted on the bore of 
ffun eofthe §> nn terms of the number of square inches in its sectional area, by 
