53 



THE POPULAR SCIENCE MONTHLY. 



his time. The sectional steam-boiler only just becoming a standard 

 type ; high-pressure steam with condensation has just become gen- 

 erally adopted ; the screw only came in use forty years later, when 

 Ericsson, Smith, and Woodcroft, came forward with it, and twin- 



Fig. 55. Machinery of Twin-Screw Steamer or 1804. 



screws are hardly yet familiar to engineers. The revolving battery 

 protected by iron plating is another of what are generally considered 

 recent devices ; and the peculiar Stevens revolving ship is reproduced 

 by Elder sixty years later. 



A model of the little steamer built in 1804 is preserved in the 

 lecture-room of the department of mechanical engineering at the 

 Stevens Institute of Technology, and the machinery itself (Fig. 55), 

 the high-pressure " section " or " safety " tubular boiler as it would 

 be called to-day, the high-pressure condensing engine with rotating 

 valves, and with twin-screw propellers, is given a place of honor in 

 the model-room or museum, where it contrasts singularly with the 

 mechanism contributed to the collection by manufacturers and invent- 

 ors of our own time. 



94. The first of Stevens's boats performed so well that he immedi- 



Fig. 56. Stevens's Twin-Sckewb, 1S05. 



ately built another one, using the same engine as before, but employing 

 a larger boiler, and propelling the vessel by ticin-screws (Fig. 56 '), the 

 latter being another instance of his use of a device brought forward 

 long afterward as new, and since frequently adopted. 



1 These cuts are facsimiles of steel engravings made for Stevens. 



