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THE POPULAR SCIENCE MONTHLY. 



Western rivers, all steamers were then propelled, as they are still, by 

 condensing engines. The instrument of propulsion was also, even in 

 Stevens's own boats after his earlier experiments, the paddle-wheel. 

 The use of the screw did not become general, even in deep water, 

 until within the last twenty years. 



96. The steam-engine in most general use for sea-going ships when 

 the introduction of the screw compelled its withdrawal, with the pad- 

 dle-wheel which it drove, was that shown in Fig. 57, which repre- 

 sents the side-lever engine of the steamer Pacific, as designed by 

 Charles W. Copeland. 



In the sketch, A is the steam-cylinder; B C the side-rods, or 

 links, connecting the cross-head in the piston-rod with the end-centres 



Fig. 57. The Side-Lever Engine, 1849. 



D, of the side-lever D E F, which vibrates about the main centre 



E, like the overhead beams. A cross-tail at G is connected with the 

 side-lever and with the connecting-rod G If, which latter communi- 

 cates motion to the crank I /", turning the main shaft J. The air- 

 pump and condenser are seen at 31. This engine w r as one of the 

 earliest and best examples of the type, and perhaps the first ever 

 fitted with a framing of wrought-iron. 



97. After the experiments of Stevens, we find no evidence of the 

 use of the sci-ew, although schemes were proposed and various forms 

 were even patented, until about 1836. 



In 1836 Francis P. Smith, an English farmer, who had become 



