MECHANICS AND USEFUL ARTS. 



73 



Taking 60 as the constant, and the area of the bottom and upper 

 deck as 1,060 square inches, we have 



1,060x60x60 



- - 



340 



=11, 223 tons, 



as the weight that would break her in the middle. Let us now take 

 the new ship, and give her the same area top and bottom, and again 

 we have 



__, 1,060X46X60 



W = - -- = 5,851 tons ; 



500 



which is a little more than half the strength. From this it is obvious 

 if we are correct in our calculations that the utmost care and at- 

 tention is requisite in design and construction to insure stability and 

 perfect security in the build of ships. 



Resistance of Iron to the Penetration of Shot. The next question 

 for consideration is the properties of iron best calculated to resist the 

 penetration of shot at high velocities ; and in this I am fortunate in 

 having before me the experiments of the Committee on Iron Plates, 

 which had the following properties: Specific gravity, 7.7621; ten- 

 sile strength in tons per square inch, 24.802 ; compression per unit of 

 length in tons, 14,203 ; statical resistance to punching in tons, one- 

 inch plate, 40.1804. 



The specimens subjected to compression gradually squeezed down 

 to one-half their original height, increasing at the same time in diam- 

 eter till they attained ninety tons on the square inch. In these ex- 

 periments, four descriptions of iron were selected, marked A, B, C, D : 

 the two first and last were taken from rolled and hammered iron 

 plates, excepting C, which was homogeneous, and gave higher results 

 to tension and dead pressure than the others. 



In density and tenacity they stood as follows : 



Here it will be observed that the strengths are in the ratio of the 

 densities, excepting only the B plates, which deviate from that law. 

 On the resistance to compression, it will be seen that in none of the 

 experiments was the specimen actually crushed ; but they evidently 

 gave way at a pressure of thirteen to fourteen tons per square inch, 

 and were considerably cracked and reduced in height by increased 

 pressure. 



From the experiments on punching we derive the resistance of 

 7 



