PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 655 



shot of 120 lbs. Again, Mr. Stevens, after a long series of experi- 

 ments, proposed to meet this increased efficiency of the gun by 

 an increased resistance, and in 1854, the keel of the present ship 

 was laid, which is about 400 feet long and 45 feet beam, with a 

 displacement of about 6,000 tuns at 20 feet immersion, to be 

 propelled by two screws of 20 feet diameter and 25 feet pitch, 

 driven by eight engines, 45-inch bore and 3 feet 6 inches stroke, 

 designed to make 100 revolutions per minute. With boilers capa- 

 ble of keeping steam at from 50 lbs. to 60 lbs., this would give 

 an effect of from 8,000 to 10,000 horse-power. This, with a model 

 of great beauty, will give her a speed that would enable her to 

 run down any ship that floats at this day. The battery, which, 

 in fact, is the only part that is above the water, occupies only a 

 section of about 60 or 70 feet in length amidships, and rises about 

 20 feet above the water line, containing a working deck, beside 

 an upper deck designed to be bomb-proof. The sides are pro- 

 tected by combined plates of iron 8 inches thick, with the space 

 between them and the ship's sides (about two feet) to be filled in 

 by alternate layers of wood and rubber. I would note here that 

 Mr. Stevens found the best wrought iron plates 7 inches solid 

 thickness could be shivered and broken by a 120-lb shot at short 

 range. The fracture of one of these plates that I remember 

 seeing, presented the appearance of cast iron, rather than fine 

 wrought iron. This ship carries no mast, and is not designed for 

 cruising or foreign service ; nor do I believe any of her trans- 

 atlantic imitations are fit for such service, for the reason that, 

 when furnished with armament and stores, they would have but 

 limited capacity for coal. The ship I have attempted to describe 

 has so far progressed that she may be completed and made ready 

 for service in from three to four months. 



Mr. Bartlett said that the credit of introducing and provig the 

 practicability of iron clad ships was fully awarded to Mr. Ste- 

 vens by the London Quarterly Review. The English experiments 

 seemed to show that almost any number of thin plates riveted to- 

 gether could be pierced, but that a solid plate 4^ inches thick 

 was almost shot proof. He thought that the eight inch plates 

 experimented upon by Gen. Totten were proof against any mis- 

 sile ever yet discharged, when the plates were backed by solid 

 masonry. 



Mr. Stetson believed that the idea of iron plated ships origin- 

 ated in America. Mr. Stevens tried thick iron, and afterward 



