MECHANICS AND USEFUL ARTS. 73 



the hammer ; a nicely-adjusted balance is provided by a massive iron 

 lever, one end of which is welded into and forms part of the metal, 

 and this is provided with a dozen or more of horns or handles, by 

 which the iron can be turned in any direction ; for the plates are 

 not only hammered on the broad surface, but at the sides and at the 

 top and bottom. The plates, after having been roughly formed into 

 shape, are completely planed and squared. Planing machines of 

 enormous size hug these plates in their resistless arms, and bear them 

 slowly and silently under the sharp cutting edges of the tools, and 

 thin shavings of the metal, which as they are cut coil up in long bright 

 ringlets of iron, attest the tremendous power of these noiseless and 

 all but omnipotent machines. When the edges and surfaces are 

 made perfectly smooth, like the finest work of the cabinet-maker, 

 the plates are placed on an end, gripped firmly by a mortising ma- 

 chine, and, as they travel slowly backward and forward in the frame- 

 work against a small tongue of steel, a groove of about one inch in 

 width and depth is formed, into which the corresponding projections 

 formed on the side of another plate will fit with the most perfect ac- 

 curacy, the plates all being made to dovetail on each of the four sides." 



THE EEICSSON BATTERY. 



At the July session of the U. S. Congress an appropriation of $1,- 

 500,000 was made for building iron-clad vessels, under a provision 

 that three naval commanders were to approve of all plans before be- 

 ing adopted. The Secretary of the Navy accordingly appointed Com- 

 modores Smith and Paulding, and Captain Charles H. Davis to exam- 

 ine and report on the several plans submitted by engineers and ship- 

 builders. Among others, Captain Ericsson appeared before the com- 

 mittee with a plan of an impregnable battery, which was at once 

 adopted, and the construction of the same was ordered by the Secre- 

 tary of the Navy, with a stipulation that the work was to be com- 

 pleted within one hundred days from the signing of the contract, viz., 

 October 5th, 1861. There was also another stipulation in the con- 

 tract of a most remarkable character, and probably without a prece- 

 dent, viz., the trial of the efficiency of the battery must be made under 

 the guns of the enemy's batteries at the shortest ranges ; the United 

 States to furnish guns and ammunition, as well as officer's and men. 

 Avoiding as far as possible all technicalities, the leading features of 

 this new battery may be described as follows : The hull is sharp at 

 both ends, and instead of the gradual curve of a cutwater the bow pro- 

 jects, and coming to a point at an angle of eighty degrees, the sides, 

 instead of the ordinary bulge, incline at an angle of about fifty-one 

 degrees to the vertical line. ThigLhull is flat-bottomed, six feet six 

 inches in depth, and built quite light, of three-eighth-inch iron. It is 

 one hundred and twenty-four feet long and thirty-four feet wide at the 

 top. 



Resting on this is another, or upper hull, also flat-bottomed, with 



perpendicular sides and pointed ends. It is forty-one feet and four 



inches wide, so that it juts over the lower hull on each side three feet 



and seven inches. It is one hundred and seventy-four feet long, thus 



7 



