PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 499 



same time to admit of its being forced through the plate. But we must 

 bear in mind that, in order to effect this object, the fibres of tlie iron plate 

 must be secured from reaction by placing it upon a firm and unyielding 

 support, and that otherwise it would be impossible to punch the plate. 



Thus, from all the facts that can be collected bearing upon this subject, 

 we are irresistibly led to th<3 conclusion that whatever may be the means 

 or instruments emploj^ed to penetrate iron plates, one thing is essential, 

 that the fibres of the iron must be prevented from reaction, in order to 

 avail, ourselves of the greatest effect of the percussive force applied, and 

 that if we wish the plate to oppose its maximum powers of resistance to 

 penetration, some elastic substance must be interposed between the iron 

 plate and its solid support to allow the fibres of the iron to react. 



There is good reason to believe that the interposition of an elastic sub- 

 stance between the iron and the wood, renders the elasticity of the latter 

 more available by preventing the fibres of the wood from being cut and 

 divided, thereby increasing the power to resist penetration by enhirging 

 the base of resistance at the point of impact, on the principle of diffusing 

 the force of the blow over a greater extent of surface. 



The advantages obtained by this proposed combination, as well as the 

 quantity of materials required to resist different sized shots, can be ap- 

 proximately determined by calculation based upon hypothesis, or experi- 

 ments. For example: A cannon ball of a given weight, pi-ojected by a 

 given force, exerts certain power at a given range or distance from the 

 guns. With data similar to this before us, it will be an easy matter to 

 make experiments sufl&cicnt to determine all that is necessary, provided 

 the departments are not satisfied with experiments that have been made. 



It may be urged by some that similar experiments have been made at 

 the navy yard in Washington, or at other points, and that the results were 

 unsatisfactory. This will not be surprising, when the facts are known, as 

 one of our acting rear-admirals remarks in an official eommunication, to which 

 he says he "was a witness, in Washington city. Heavy tuiTCts with four- 

 inch iron plating were placed in front of aPalilgren eleven-inch; also the 

 same with a two-inch coating of India rubber. At direct firing and at an 

 angle of 35 degrees, the gutta-percha was proved to be a useless expense, 

 having no effect whatever to resist the shot ^nd rifle shell, both of which 

 were repeatedly tried." 



It must be admitted that " gutta-percha" is a " useless expense," for 

 this purpose, as it is hard and somewhat brittle; consequently will not 

 successfully resist percussive impetus, and is not as susceptible of being 

 compressed as vulcanized India rubber. Also a plate of India rubber one 

 inch in thickness, is said to have been " placed behind a four (4) inch plate 

 of iron, backed by sixteen inches of oak, at fifty feet. The first trial was 

 at an angle of forty-five degrees; the shot did not penetrate. The second 

 was perpendicular, the shot penetrated wood and all." This firing was 

 also done with eleven-inch solid shots from a Dablgren gun. Had these 

 four-inch plates of iron been manufactured into sheets one inch in thick- 

 ness, of good tough and fibrous qualities, and alternately arranged with 

 sheets of vulcanized India rubber, as herein proposed, there is no doubt 



