656 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



chose a series of thin iron plates. Gen. Totten used thick iron 

 for earthwork; the English had applied the same thick iron to 

 ships. But Whitworth's projectile had punctured the thick iron 

 plates in England, and it was a question whether a single plate 

 could be made tough enough. A thick mass of iron could not be 

 forged so as to produce the same effect on the interior as near the 

 surface with the present forge hammers. There was no way of 

 rendering the interior as strong as the surface. 



Capt. Bartlett believed that a vessel could be built to float in 

 the bay of New York that no shot would penetrate, but yet it 

 would not be invulnerable. It was well known that granite reefs 

 were removed several feet under water by the Aveight of water 

 only and a sufficient quantity of powder. A single shell would 

 be sufficient to destroy a bomb-proof vessel if it could be exploded 

 under the ship. When Mr. Stevens first appeared at Washington 

 with his plans for an iron-clad vessel, Commodore Stockton de- 

 clared that he would be able to bore it with his improved cannon. 

 It had been settled that an iron plate, eight inches thick, would 

 resist any shot at present used. Fortifications could be built 

 strong enough-to break any shot for a given time ; but any forti- 

 fication could be taken at last by shot and shell from a land bat- 

 tery. It was merely a work of time. So iron plates, being bat- 

 tered for a length of time, would become brittle and give way. 

 Iron-clad ships were not practicable for cruising — only for harbor 

 defence. Capt. B. exhibited some of Gen. James' projectiles, of 

 which he spoke last week. The shot was covered with canvas, 

 underneath which was a tin casing, and underneath the tin cas- 

 ing was a quantity of lead. The lead was run into the hollow 

 part of the shot, and through several longitudinal openings to the 

 tin casing on the outside. The first efiect of the explosion is to 

 expand the lead, and thus destroy the windage, the same as the 

 Minie ball. As soon as the shot comes out of the cannon, the tin 

 casting is thrown ofi". The shot goes out on a half-turn from the 

 rifling of the gun ; then as soon as the tin and lead are stripped 

 off there are rifling grooves in the shot that come into pla3^ The 

 largest of the shot exhibited weighed 81^ lbs. ; it was carried by 

 an ordinary 42-pounder with a charge of 10^ lbs. of powder, at 

 5 degrees elevation, a distance of 2,221 yards, and went through 

 52 inches of solid oak. A small plunger inside contains a percus- 

 sion cap, which causes an explosion the instant the shot strikes 

 an object ; even a sand-bank will cause an explosion before the 

 Bhot enters three inches. The shot then splits longitudinally. 



