114 THE WATT AND THE TREVITHICK ENGINES. 



CHAPTER XX. 



THE WATT AND THE TREVITHICK ENGINES AT DOLCOATH. 



HAVING up to 1816 traced the progress of the steam- 

 engine in Cornwall through a century, during the 

 latter half of which Trevithick, sen., and his son were 

 among its most prominent improvers, the latter having 

 devoted a quarter of a century to the work, the effect 

 of which is shown in the skeleton outlines of a few 

 classes of engines, one important feature still remains 

 for examination before a correct judgment can be 

 formed of the events of this period and their prime 

 movers. 



The use of an increasing pressure of steam gave 

 increased force arid value to the improved steam-engine, 

 but the power of constructing engines and boilers to 

 render the increased pressure manageable was the result 

 of a lifetime of labour. 



Savery, whose engine was scarcely more than a 

 steam-boiler, failed to control its force, and is said to 

 liave blown the roof from over his head. The mecha- 

 nism of Newcomen's engine was well arranged, but 

 suitable only for the working of pumps, and its power 

 was limited to the weight of the atmosphere, from which 

 it was called the atmospheric engine. 



In 1756, an atmospheric engine with a cylinder of 

 70 inches in diameter worked at the Herland Mine, 

 " the only objection to which was the cost of the coal, 

 to lessen which several methods had been suggested 



