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THE POPULAR SCIENCE MONTHLY. 



cross-beams, b b. The air-pump m I o p, the tank n, and valve-gear 

 q r s, are quite similar to those of the beam Cornish engine. The bal- 

 ance-beam is seen at h i. 



Fig. 18. Bull's Coenish Engine, 1T98. 



Fig. 19 represents another form of 

 pumping-engine which belongs to the 

 class known as the "compound" or 

 " two-cylinder " engine. 

 This class of engines, in which the steam exhausted from one 

 cylinder is further expanded in the second, was first introduced by 

 Hornblower, in 1781, and was patented, in combination with the Watt 

 condenser, by Woolf, at a later date (1804), with a view to adopting 

 high steam and considerable expansion. 



The Woolf engine was to some extent adopted, but was not suc- 

 cessful in competing with Watt engines where the latter were well 

 built, and, like Hornblower's engine, was soon given up. 



The compound engine has come up again within a few years, and, 

 with what is now considered high steam and considerable expansion, 

 and designed with more intelligent reference to the requirements of 



