MECHANICS AND USEFUL ARTS. 55 



probably two of them. It was necessary to place those magazines of 

 powder so that when you saw the vessel in that range you had only to 

 bring the two poles of the galvanic battery together and make the ex- 

 plosion. There was, as already stated, a difficulty in using gunpowder. 

 But since gun-cotton had the remarkable effect of destroying a vessel 

 he did not know her strength at a distance of eighteen feet, and 

 that not vertically, but laterally, the question arose whether they might 

 not fortify and protect those channel ways by placing a ring of gun- 

 cotton magazines along the bottom ; but, at any rate, if that was not 

 necessary, they could float them at any depth, and out of reach of the 

 vessels generally using the channel. That appeared to him to be one 

 of the most important uses of gun-cotton, and it was one which would 

 give safety to cities which were some distance from the mouths of nav- 

 igable rivers. Admiral Belcher stated that the explosion of powder 

 under water was once done under one of his own vessels to clear away 

 ice. He placed it upon the ground, thinking that its explosion would 

 blow the ice clear of her bows without touching the vessel. There 

 was, however, sufficient water to form a cushion, and when the explo- 

 sion took place it only produced a great wave upon which the vessel 

 rose. 



EXPERIMENTS AND RESULTS IN RELATION TO GUNS, ARMOR, 



AND PROJECTILES. 



Armor for Ships of War. Ever since iron-clad ships were invented, 

 there has been a conflict of opinions upon the subject of their armor. 

 The proper thickness, the mode of fastening it, whether single plates or 

 a number of thin ones are the best, with wood backing or without, 

 these are only a few of the questions bearing upon the subject which 

 have received attention. That some one plan has not been universally 

 adopted is owing to obvious natural causes. Each person or govern- 

 ment thinks himself or itself best qualified to judge where his or its im- 

 mediate interest is at stake. 



In this country, we have more generally adopted the series of thin 

 plates in preference to heavy single ones ; although there are some ex- 

 ceptions to this statement. In Europe, the reverse is true. Thus far 

 we have had more practical experience with iron-clad ships than any 

 other people. The last to adopt these engines of war, we have been 

 the first to put them into actual service, and our success has been wholly 

 with the combinations of thin plating. The gunboats on the Western 

 rivers Conestoga and Lexington were plated with solid iron 2J- 

 inches in thickness, yet they were completely riddled in the attack on 

 Fort Henry by the ordinary guns at that point ; so also was the Essex 

 before her reconstruction. The Ericsson batteries are all armored 

 on the principle of many layers of thin plates, and they have proved 

 themselves impregnable, so far, to every assault. The arguments in 

 favor of thin plates may be summed up in the following list: It is 

 claimed that they are stronger for a given weight of metal than thicker 

 forged armor, by reason of ^he " scale " or cuticle being preserved in- 

 tact, as well as by the intimate relations of the fibers which occur when 

 small quantities of the metal are subjected to intense pressure ; for this 

 reason it is apparent that the structure of thin plates must be, cetens 

 paribus, more reliable than forged ones. By the same reasoning, how- 



