MECHANICS AND USEFUL ARTS. 87 



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directed to meet the difficulty halfway, by protecting the mere vital shell 

 of the lower hull, so as to defy the ordinary assault of any ordinary gun- 

 bearing vessel which should not by its accumulated weight or mass of 

 matter render defence impossible. It was important, therefore, that such 

 a tonnage should be provided as should, as in the case of the Warrior class, 

 be capable of -floating the contemplated armament independent of the for- 

 ward and after compartments, which might be assumed as mere assistant 

 means of flotation, and to be so fitted with cellular divisions below the 

 level of flotation as to render injury to those parts below the reach of 

 shot of very trifling importance. 



Assuming that an iron spherical shot of thirteen inches was the missile 

 to be dreaded, the question to be considered was not exactly what flat 

 plate of iron was to resist it, for the authorities stated that no reasonable 

 thickness, even up to 12 inches, would withstand the impact. Looking, 

 however, only to the floating carcass of the ship, and disregarding the 

 ports until we had an impregnable stage on which to place guns, then we 

 should be at liberty to increase the thickness to any amount. His prop- 

 osition was to construct the ship on the customary plan of close iron rios, 

 but filling up the interstices between the iron with condensed teak. As- 

 suming that we constructed a ve-sel with 36 inches depth of rib at the 

 vulnerable portions which shot could reach, which would probably involve 

 12 vertical feet of her side. say eight feet below water and four feet 

 above, we should then have a vessel of stronger framework than any 

 now built, building, or in contemplation. Then assuming that thase iron 

 ribs presented two inches ;.t the exterior, tapering in 36 inches to one in- 

 side, placed six inches asunder, and filled in with compressed timber or 

 other matter, we should have per cubic yard of bulwark 3,412.125 

 pounds, that of the Warrior being 3,123 pounds, showing only a differ- 

 ence of about 290 pounds to the cubic yard. 



It was yet to be determined, by actual experiment, whether that resist- 

 ance would offer the protection sought. Perhaps it would not, but as he 

 proposed to add a six-inch planking outside, he considered that the com- 

 parative danger with our pr sent iron-clads would be reduced to nil, or 

 at le.st to something which would satisfy the seamen. On a previous 

 occasion he had alluded to paper as an opposing medium. In 1816, at 

 Algiers, a ream of foolscap, end on, resisted a 68-pound shot from a 27- 

 feet gun, at 76 yards; and in 1854, he proposed to the Admiralty to con- 

 struct movable battery rafts of brown paper, but the design was not car- 

 ried out. Lately, he learned from a newspaper that, ten years after his 

 proposal, it was found that paper of one inch thickness was fired at and 

 not quite penetrated, while a similar shot went quite through ten inches 

 of g )od otk. In conclusion, he would observe that condensed millboard 

 weighed less than oak or teak, and, interposed in the manner he had sug- 

 gested, might form a target which would set even the largest ordnance at 

 defiance. 



Ericsson on tJie Construction of Impregnable Armor. The fol- 

 lowing is an extract of a letter recently addressed to the Secretary of 

 the Navy on the above subject by Mr. Ericsson: "The English 

 have failed in producing an armor capable of resisting projectiles of 

 great speed and weight. Solid blocks of wrought iron, of the best 

 quality, one foot in thickness, have been split under the impact of the 

 projectile. The enormous dynamic force lodged in the shot, com- 



