MECHANICS AND USEFUL ARTS. 49 



of repair, after which the water might be pumped out and the ship 

 freed. 



The same subdivision of decks which affords the security against 

 entire submersion, ensures protection against total destruction by fire. 

 In the event of a fire's being discovered on either deck, the hatchway 

 of that deck would be fastened down, and, the supply of air being 

 thus cut oif, the fire would die out of itself; or if the fire had got too 

 much hold upon the ship to allo\v of this, then the entire deck in 

 which the conflagration was raging might be filled with water with- 

 out risk of other inconvenience than that of having to pump it out 



again. 



The practice of dividing iron ships into water-tight compartments, 

 with the view of preventing their sinking, has been followed for many 

 years, but the division walls have, in all cases, been transverse ; that 

 is, each deck has been divided by water-tight iron bulkheads into 

 three, four, or more separate rooms or apartments, the impression 

 being that should one or two become by leakage filled with water, 

 there would be buoyancy enough in the others to keep the ship afloat. 

 Experience has, unfortunately, however, and the case of the Con- 

 naught is a prominent instance among many, proved the unsound- 

 ness of this theory. The fact is, that when any one of the compart- 

 ments becomes filled with water, the vessel is unduly depressed, and 

 no longer sails with an even keel ; but by making the decks them- 

 selves the water-tight divisions, the weight of the water, in case of 

 leakage, is equalized over the whole surface of the ship, and the even 

 keel, which is the main element of safety, is preserved. 



PKOGKESS OF IMPROVEMENT IN WAR IMPLEMENTS AND CON- 

 STRUCTIONS. 



During the past year, the perfection of heavy ordnance, of projec- 

 tiles, and of the art of defence, have constituted the chief topics of 

 interest and experiment with the naval and military authorities of 

 both Europe and America ; but in spite of the most earnest and long- 

 continued investigations on the part of different governments, " so 

 little," says Capt. Dahlgren, in his official report to the secretary of 

 the navy, Dec. 1st, 1862, "is yet positively known of the effect of 

 ordnance and the resistance of iron plates in different forms, that the 

 ablest and most experienced cannot agree in regard to the armor best 

 calculated to oppose the most effectual resistance, or upon the can- 

 non that shall be employed to overcome that resistance." 



At the close of the year 1861, the general opinion in Great Britain 

 and on the continent of Europe (founded on the " results of the 

 experiments at that time made public) was, that ships of war pro- 

 tected by iron plating four and a half inches in thickness were essen- 

 tially invulnerable to the effects of shot and shell. (See Annual of 

 Scientific Discovery, 1862, p. 84.) 



In the spring of 1862, Sir William Armstrong having completed a 

 new one-hundred-and-fifty-pound smooth-bore gun, additional experi- 

 ments were made, under the direction of the English board of admi- 

 ralty, and in the presence of a large number of scientific, military, 

 and naval men, including agents of several foreign governments, 

 5 



