PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 495 



the range I desired. Here is a drawing of the target as I proposed to 

 erect it before I received an order from Admiral Dahlgren for its construc- 

 tion. The range proposed by me was three hundred yards for the first shot, 

 and to fire at it on a boat, so that the range and position could be changed 

 but Mr. Fox was of opinion that we could not get practical results without 

 setting the target against a bank at a range of fifty to seventy-five 

 feet. 



There are good reasons for believing that iron plates lose their fibre or be- 

 come crystallized from the effects of the percussive impetus of shot. 



The iron on the target composed of iron and India rubber and fired at as 

 described, was convex some three inches by the reaction of the elastic 

 cushions, round the point of impact. Yet no bolt was broken in conse- 

 quence of the elastic washers. Elastic substances under plate armor will 

 successfully resist concussion. This is demonstrated every day on our 

 railroad cars by the vulcanized India rubber car spring. 



The advantages to be derived from elastic backings is no longer a 

 theory. Its value has been well tested. It is in use on the forward case- 

 mates of the gunboats Essex, Lafu3'ette and Choctaw; and to Commodore 

 W. D. Porter belongs the credit of introducing it in the navy, by giving it 

 a good practical test on the Essex, the first iron-clad vessel fitted out in 

 America. 



I will now read the statement and affidavit of Mr. Kilpatrick, dated 



Haines Bluffs, April 30, 1863. 



Mr. Jones — Dear Sir : We have just been fighting, three hours and forty 

 minutes. The Choctaw stood it pretty well. She was struck on the turret 

 six times, once with a ten inch shell, when it struck it dented the iron and 

 rebounded back, and struck the deck, where it biirsted, setting fire to the 

 deck, forward of the magazine. The men had to go out and water it out, 

 the rebels firing heavy at them. This proved the elasticity of your patent 

 gum. The other four shots glazed without doing any harm. There was 

 one ten inch shot which struck her on the angle of the turret crown, it 

 went right through, but you must remember there was no gum behind the 

 iron on this part of the turret, as we only put the gum on the front of the 

 turret. She was struck seven times on the star-board side, two of the shots 

 ■went through into the cabin. Where there was no gum, it smashed the 

 iron so badly, that I had to put the men to work and cut it out, and patch 

 it. The officers thought the gum was of no account, so they would not have 

 it on all the important parts, but they think it is great stuff now. I forgot 

 to mention the distance that the captain supposed we were from the rebels' 

 batteries; he said they were 400 yards off. Wo were struck fifty-six times 

 in all. The chimneys are completely riddled, and the wheel-houses have got 

 their share. By the by, I was nearly forgetting to tell you there was one 

 shot, a sixty-four pounder, it went through eleven feet of solid timber, in 

 the wheel-house. There was no iron here. The officers thought when they 

 saw that, that your gum and iron is a great institution. 



I remain, yours truly, 



ALEXANDER KILPATRICK. 



To Mr. J. L. Jones, St. Louis, Mo. 



