BOILERS FOR STATIONARY ENGINES.

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In the Perkins System of boiler a large number of water tubes areenclosed in a double shell of plate iron, the space being filied with anon-conducting medium. The tubes are 2inches inside diameterand $4 inch thick. About one half of the tubes are used for generat-ing steam, the other half being used for superheating. The boiler issupplied with distilled water, and the furnace is placed beneath thetubes which run vertically above. Tubulous boilers have been triedat sea in the P}'opontis and other vessels on Rowan’s System, andagain recently in the steam yacht Anthracite, which lately madea voyage across the Atlantic and back, carrying a pressure of from300 to 500 Ibs. of steam per square inch. This vessel was fittedwith the Perkins boiler.

ON BOILERS, BY FAIRBAIRN.

We propose under this head to consider the steam-boiler in itsconstruction, management, security, and economy.

As regards the construction, it is absolutely necessary to studycarefully the shapes which give maximum strength, and requireminimum of material. In boilers this is most important, as anyincrease in the thickness of the plate obstructs the transmissionof heat, and exposes them as well as the rivets to injury on the sideexposed to the action of the flame. It has been generally supposedthat the rolling of boiler plates gives to the sheets greater tenacityin the direction of their length than in that of their breadth. This is,however, not always the case, as experiments show that the tensilestrain across the fibre of boiler plates is in some samples greater thantheir tensile strength when torn asunder in the direction of the fibre.We consider this may be owing to the way the iron is piled beforeputting it through the rolls; more recent experiments plainly showthat the tensile strength of boiler plates is slightly greater in thedirection of the fibre, and from this it would appear that althoughit is more convenient to construct circular boilers, with plates rolledin the direction of the fibre, still we think that boilers diagonally

plated are the strongest.

Next to the tenacity of the plates comes the question of rivet-ting. On this point we have been widely astray, and it requiredsome skill, and 110 inconsiderable attention in conducting the ex-periments, to convince even some practical men that the rivettedjoints were not stronger than the plate itself. In punching holesalong the edge of a plate, it is obvious that the plates must be