TIIK WATT AM) TI1K TKKVITUICK KXUINKS. 123 



steam-engine increased more rapidly beyond than within 

 the limits of Cornwall, for in 1802 was erected at 

 Coalbrookdale a high-pressure steam-puffer engine, to 

 which Trevithick attached a pump which forced water 

 through a column of upright pipes, that the power of 

 the engine might be accurately measured. It worked 

 with steam of from 50 to 145 Ibs. on the inch, and 

 wholly discarded the vacuum which had been Watt's 

 mainstay. 



" The boiler is 4 feet diameter, the cylinder 7 inches diameter, 

 3-feet stroke. The water-piston is 10 inches in diameter, draw- 

 ing and forcing 35 feet perpendicular, equal beam. I first set 

 it off with about 50 Ibs. on the inch pressure against the steam- 

 valve, for the inspection of the engineers about this neighbour- 

 hood. The steam continued to rise the whole of the time it 

 worked ; it went from 50 to 145 Ibs. to the inch. 



" The engineers at this place all said that it was impossible 

 for so small a cylinder to lift water to the top of the pumps, 

 and degraded the principle, though at the same time they spoke 

 highly in favour of the simple and well-contrived engine. 



" After they had seen the water at the pump-head, they said 

 that it was possible, but that the boiler would not maintain its 

 steam at that pressure for five minutes ; but after a short time 

 they went off, with a solid countenance and a silent tongue." L 



This high-pressure steam pumping engine in 1802 

 may be taken as the first pumping engine of the puffer 

 class using such strong steam. 



In the spring of the following year 2 a somewhat 

 similar engine was erected in London. " The cylinder 

 is 11 inches in diameter, with a 3^-feet stroke. It re- 

 quires the steam at a pressure of 40 to 45 Ibs. to the 

 inch to do its work well, working about twenty-six or 



1 Sec Trevithick's letter, August 22nd, 1802, vol. i., p. 153. 

 * See Trevithick's letter, May 2nd, 1803, vol. i., p. 158. 



