STEAM-ENGINF, 113 



placed vertically or horizontally. Having during 

 twelve busy years constructed over a hundred high- 

 pressure steam-engines, scarcely any two of which were 

 exactly alike, he departed if possible still further from 

 the Watt type, and went back apparently, though not 

 in reality, to the Newcomen engine, simplifying it by 

 the omission of the great bob, and use of condensing 

 water, as in the nautical labourer and steamboat engine 

 of about 18 10, 1 and the South American mine engines 

 of 1816, 2 which had open-top cylinders, more like a 

 Newcomeii than a Watt, but if possible even more 

 simple and primitive-looking than the former. Again, 

 compare the thrashing engine of 1812 3 with the New- 

 comen of 1712 : 4 the great and all-important difference 

 being that one was a high-pressure steam-engine, the 

 other a low-pressure atmospheric engine. Then came 

 the varieties of high-pressure steam pole-engines, work- 

 ing very expansively either as puffers or condensers, 

 retaining the same dissimilarity to the Watt engine : 

 and lastly, the combination of the high-pressure pole 

 with the Watt patent engine, thereby causing the 

 old Watt engine to do more than double the work 

 it had done when new from the hands of the maker, 

 and also to perform this increase of work with a de- 

 crease in the consumption of coal. 



The following chapter will trace the adaptation of 

 high-pressure expansive steam, from cylindrical boilers, 

 to the form of pumping engine still in general use. 



1 See vol. i., p. 3b6. 2 See chap. xxi. 3 Vol. ii., p. 37. 



4 Vol. i., p. 5. 



VOL. If. 



