MECHANICS AND USEFUL ARTS. 99 



which could be bent and unbent; and a process for making malle- 

 able glass seems to have been known in the 16th century. 



Improvements in Locomotive Boilers. Should the attempts to 

 roll locomotive boilers in one single tube, without seam or joint, 

 prove successful, a great gain in strength will be effected, with 

 the probable disappearance of "furrowing," which usually ap- 

 pears along a seam of rivets. Steel boilers, with welded joints 

 and without rivets, are coming into use, which will enable engi- 

 neers to use steam at higher pressures and to work it more expan- 

 sively. 



ON SHIPS OF WAR. 



Mr. John Bourne, at a meeting of the London Institution of 

 Civil Engineers, in January, 1867, read a paper on "Ships of 

 War." In his opinion, the only vessels capable of carrying suffi- 

 cient thickness of armor to resist modern ordnance, Avere those 

 built on the monitor or turret system, the invention of Capt. John 

 Ericsson, of New York. He maintained that, although broadside 

 vessels might be useful and even necessary, yet that no broadside 

 fleet would be safe unless accompanied by a flotilla of monitors. 

 It was simply a question of preponderance of forces ; and in any 

 future maritime war the strongest armor and the heaviest guns 

 must necessarily prevail. He proposed that any monitors now to 

 be built should have side armor 18 inches thick, backed by 4 feet of 

 oak, and a turret 24 inches thick, carrying 2 20-inch wrought- 

 iron guns. He considered that ample experience showed that such 

 vessels were seaworthy, afforded comfortable accommodation for 

 the crew, were healthful, and popular with sailors. In the com- 

 mon iron-clad, as the armor had to be spread over a high side, it 

 was necessarily thin and weak ; whereas in the monitor, the sides 

 being very low, the area to be protected was reduced to a mini- 

 mum, so that with the same displacement the armor might be 

 made of great thickness, such as would be impenetrable by the 

 "heaviest existing ordnance. The " Kalamazoo " class of monitors 

 had side armor 14 inches thick, backed by several feet of oak, and 

 these vessels possessed great facility of evolution, as they were 

 fitted with balanced rudders and twin screws. In both the armor 

 and the guns, the broadside system was one of diffusion, the tur- 

 ret or monitor system one of concentration ; the former had been 

 adopted in England and France, the latter in America. In the 

 broadside system the only material innovation on the model of the 

 old men-of-war was in the application of iron armor to the sides ; 

 in some cases the armor was not extended to the bow and the 

 stern, but only the central part of the sides and a belt at the water- 

 line were protected, and armor bulkheads were carried across the 

 ship, before and behind the protected portions of the sides, so as 

 to form the central part of the vessel into a rectangular fort. On 

 this principle the "Bellerophon" and other recent vessels had been 

 built, and its advantage was that it enabled thicker armor to be 

 applied. In the monitor system the guns, of large calibre, are 

 carried in one or two cylindrical iron towers, and the weight of 



