44 ANNUAL OF SCIENTIFIC DISCOVERY. 



mast is formed of three curved plates half an inch in thickness, which 

 form the skin or outside shell of each, the joint where the vertical 

 edges of the plates meet being so formed that the outsides of the masts 

 show no ridges. Under each of the vertical joints three strong tie- 

 irons are placed to which are riveted the plates forming the mast ; the 

 rivets on the outside being countersunk or let in Hush, the exterior of 

 the mast consequently presenting a round and perfectly smooth sur- 

 face. Experience has shown that iron masts last much longer than 

 wooden, that they are lighter and stronger, serve as valuable ventila- 

 tors, and are also better conductors of electricity. If they are shot 

 away and fall overboard they will immediately sink, instead of floating 

 alongside and fouling the screw, as is the case with wooden masts. 



Enormous Iron Plate. Messrs. John Brown & Co., of the Atlas 

 Works, Sheffield, England, have succeeded in rolling an iron plate, 

 six feet by seven feet and tliirteen and a half inches thick. The idea 

 of manufacturing so enormous a plate originated, we believe, with 

 Captain Inglis, of the Royal Engineers, with a view of ascertaining 

 if it would be desirable to protect casemates with such a powerful 



covering. 



THE STRENGTH OF WROUGHT-IRON GIRDERS. 



The strength of wrought-iron girders has been critically examined by 

 Mr. Win. Fairbairn, F.R.S. He says from his experiment it is evident 

 that wrought-iron girders of ordinary construction are not safe when 

 submitted to violent disturbances equivalent to one-third the weight 

 that would break them. They, however, exhibit wonderful tenacity 

 when subjected to the same treatment with one-fourth the load ; and 

 assuming, therefore, that an iron girder bridge Avill bear with this load 

 12,000,000 changes without injury, it is clear that it would require 328 

 years, at the rate of 100 changes per day before its security was af- 

 fected. It would, however, be dangerous to risk a load of one-third 

 the breaking weight upon bridges of this description, as, according to 

 the last experiment, the beam broke with 313,000 changes : or a period 

 of eight years, at the same rate as before, would be sufficient to break 

 it. It is more t!i:m probable that the beam had been injured by the 

 previous 3,000,000 changes to which it had been subjected ; and, as- 

 suming this to be true, it would follow that the beam was undergoing 

 a gradual deterioration which must some time, however remote, have 

 terminated in fracture. 



WELDING BY HYDRAULIC PRESSURE. 



; ' Experiments have lately been made at Paris by M. Duportail, en- 

 gineer, to ascertain whether iron might be welded by hydraulic press- 

 ure instead of by the sledge-hammer. The latter, indeed, has not a 

 sufficient impetus to reach the very core of the metal, while continuous 

 pressure acts indefinitely to any depth. In the experiments alluded to 

 M. Dun -rt:iil c:iuse;l t\v<> iron bars, one and one-half inches in diame- 

 ter, and heated !.> tlie welding point, to be placed between the piston 

 and t-se tf. j> d'an hydraulic press. The bars were welded together by 

 this means with extraordinary ease, the iron being, a> it were, kneaded 

 together, and bulged out at the sides under the pressure. The action 



