PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 619 



stroyed. Its material becomes fibrous and more dense. One variety of 

 iron made by the hammering process is known as homogeneous iron. 



After further remarks on the constitution of iron the speaker directed 

 attention to its use in the construction of vessels of war, and examined the 

 different systems of iron armor now in use. There are two prominent sys- 

 tems — one using- a plate of great thickness, called the solid-plate system; 

 the other using a series of thin plates, called the laminated system. The 

 only reason why iron is better adapted to resist a shot or projectile is that 

 it is more dense, not that it is tougher than any other material. Iron is 

 not so well adapted to resisting a sudden shock as wood is, taking equal 

 weights of each. For instance, take a plate of iron one foot square apd 

 one inch thick, weighing about forty pounds, and a piece of timber one foot 

 square, and of such thickness, or rather length, as to weigh the same as 

 the iron plate. Strike each with a hammer having the same degree of 

 force; the result will be that an indentation will be made in the iron plate, 

 and there will be a bulge or projection upon the opposite side, proving that 

 the fibrous strength of the iron was not suflScient to resist the force and 

 spi'ead it equally throughout the plate; while on the other hand the wood 

 will be dented where the hammer struck, but there will be no correspond- 

 ing bulge on the other side. 



To the late Robert L. Stevens, of Hoboken, N. J., doubtless belongs the 

 credit of proposing and partly building the first iron-clad vessel for resist- 

 ing projectiles. His plan was not so much to stop the shot, as to change 

 its direction, by causing it to glance. The Merrimac was built with the 

 same design. The same idea is carried out in the construction of the tur- 

 rets of the monitor class of vessels; but it has been found by experience 

 that a shot is not altogether ineffective which strikes but does not pene- 

 trate the armor. It has not yet been proved that vessels of this class can 

 make a sea voyage. 



Angular armor has no advantage which outweighs the disadvantages 

 attending it. For instance, suppose the hight of six feet to be plated and 

 set at an angle of forty-five degrees, the surface will be nine feet, but this 

 position of the iron does not accomplish the end intended, for a shot fired 

 from a long distance will fall nearly perpendicularly on such a surface. 

 The French were the first to attempt to practically resist the force of shells 

 fired from bombs. But the Russians were the first to inaugurate the mode 

 of horizontal shell-firing, by which they destroyed the Turkish fleet in the 

 Black Sea. The effect of this system of firing had been prognosticated by- 

 Admiral Dahlgren, and the Dahlgren gun was specially adapted to this 

 mode of attack. The increased destructive power of guns and projectiles 

 has caused a corresponding increase in the projectile armor. The ques- 

 tion now remaining is, whether the ship can be protected without destroy- 

 ing her sea-worthiness. This brings us to the examination of tho best 

 mode of resisting shot. 



If a body of a given weight and hardness meets another like it, and hav- 

 ing the same velocity, the damage is mutual; but if it meets one like it 

 which is stationary, the latter will be most injured, and will at the same 

 time receive the momentum. But if tho moving body is brought in contact 

 with a stationary one of sufficient hardness, having a weight so much greater 



