his time. The sectional steam-boiler only just becoming a standard type; high-pressure steam with condensation has just become generally adopted; the screw only came in use forty years later, when Ericsson, Smith, and Woodcroft, came forward with it, and twin-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 inventors of our own time.
94. The first of Stevens's boats performed so well that he immediately
built another one, using the same engine as before, but employing a larger boiler, and propelling the vessel by twin-screws (Fig. 56), the latter being another instance of his use of a device brought forward long afterward as new, and since frequently adopted.
- These cuts are fac-similes of steel engravings made for Stevens.