Scientific Lectures. 181 



with several of these cutters, all working at the same time. The 

 rolling of the enormous plates for the iron-clad vessels requires, also 

 tools of immense size and power. But time would fail me to describe 

 the power and majesty of these perfect, though ponderous tools. 

 They furnish to the modern engineer thunderbolts more powerful 

 than those forged for Jupiter. But they are used to build up and 

 <jreate, not to destroy. 



Military ENGmEEEmG. 

 Not long since I witnessed the penetration of a wrought-iron shield 

 for an embrasure, made of two plates measuring together fifteen 

 inches thickness, by a cannon shot of twelve inches diameter and 624 

 pounds weight, fired fi'om a constructive distance of 500 yards, and a 

 distinguished officer remarked : " Gen. Rodman has in reserve his 

 fifteen and twenty-inch guns, but American engineers and mechani- 

 cians will soon furnish us with shields strong enough to resist even 

 these enormous projectiles." The active force of the powder on the 

 ball was 40,000 pounds per square inch, equal to 2,250 tons, giving 

 it an initial velocity of 1,200 feet per second, or 800 miles an 

 hour. The weight of spherical cannon shot are as the cubes of their 

 diameters, and therefore one of twenty inches is five times as heavy 

 as one of twelve inches. The " work" of a cannon shot is in direct 

 proportion to its weight and the square of its velocity, and the efiect 

 of rifling the gun is to largely increase the effect of the shot and its 

 range. The largest American gun weighs fifty-eight tons, and throws 

 a ball of 1,072 pounds. Krupps' great steel rifled gun of fourteen 

 inches bore, weighs fifty tons and would throw a ball of 1,000 pounds. 

 It has never been fired. The largest English gun that has been tried, 

 with a moderate degree of satisfaction, is the thirteen three-tenth inch 

 Armstrong rifle, weighing twenty-six tons and throws a shell of 610 

 pounds ; but these have all burst ; and even the twelve-inch English 

 gim is as yet an experiment. The twelve-inch Rodman rifle, weighs 

 twenty-six tons and throws a solid elongated shot of 630 pounds, and 

 •even a steel shot of 684 pounds. The "Swamp Angel," used at the 

 seige of Charleston, weighed eight and one-quarter tons. It was an 

 eight-inch Parrott rifle, and threw shot of 150 poundsinto Charleston, 

 from a distance of five and one-half miles. Tlie foundation of the 

 ""Swamp Angel" was a novel one. It actually rested on fluid mud, 

 sixteen feet deep ; but the mud was confined in a square box of forty- 

 feet, made of sheet piles, driven into the sand below and made " mud 

 light." The platform of the gun (including the gun,) weighed twelve 



