Big Guns. 131 



jectile, on traversing targets i and 2, instantly let fall the pendulums 

 corresponding to these targets. 



The Noble chronoscope registers the precise instant when a 

 projectile passes certain points in the bore of the gun. The record- 

 ing apparatus consists of disks 36 inches in circumference, which 

 are made to revolve at the speed of 1,000 inches per second, linear 

 A^elocity: by means of a vernier each inch is divided into y^' -g-, a 

 linear representation is thus obtained at the circumference, of the 

 one millionth part of a second (yoTTiTTJ^ *^^ ^ second). 



Plugs of steel containing the wires of the induction coil, are 

 ■screwed into the gun, with a device at the end of the plug, so 

 that as each ])lug is reached by the projectile, the wires are cut and 

 the spark is delivered. 



Records have been obtained of plugs only 2.4 inches apart. 



From the velocities of the projectile thus obtained we can deter- 

 mine exactly the amount of pressure on each square inch of the 

 bore, due to the firing of the charge of powder, and the velocity at 

 any point of the trajectory. 



The total energy of a body in motion is the whole amount of 

 work it will produce before being brought to a state of rest, it varies 

 a^ the weight of the body multiplied by the square of the velocity. 

 This work is equal to the weight it is capable of raising one 

 foot high, and is equal to the weight in pounds of a projectile, 

 multiplied by the stpiare of the velocity in feet and divided by 

 twice the accelerating force of gravity. 



Thus, if a projectile of 165 pounds, be moving with a velocity of 

 1,470 feet per second, the work it will accomplish is 



2^^ ^' ^ z=:2^-]2 foot tons. 



64.4. 



The energy in the 2,000 pound projectile fired from the 100 ton 

 ■gun at Spezia was over 30,000 foot tons. That is to s ly, that if the 

 Italian armor-clad vessel, the "Duilio" weighed 10,000 tons, the 

 enerjry stored in the projectile of one of her own guns would lift 

 the whole ship bodily to the height of three feet. 



If the projectile should strike the turret of a monitor, which turret 

 'weighed 400 tons or so, the gearing would be so strained that 

 the turret could not work ; or when we consider there is sufficient 

 energy to lift it as high as the main-top, it requires no great stretch 

 of the imagination to understand that such a turret, with all its con- 

 tents -might be knocked clean overboard. 



