THE WATT AND THE TKEVITHICK ENGINES. 11)1 



valve-catch ; i, quadrant relieving the catch ; j\ plug- 

 rod ; k, equilibrium valve, double beat ; Z, clamp in plug- 

 rod to close equilibrium valve by its action on the handle ; 

 m, balanced lever and rod to open equilibrium valve ; n, 

 quadrant and catch relieving equilibrium valve by the 

 action of cataract-rod ; o, regulating slide on cataract- 

 rod ; p, equilibrium steam-pipe conveying steam from 

 the top to the bottom of the piston ; q, exhaust-valve, 

 double beat ; r, clamp on plug-rod, closing the exhaust- 

 valve by its descent on the handle ; s, balance lever and 

 rod, opening exhaust-valve ; t, quadrant and catch, re- 

 lieving equilibrium valve by the action of cataract-rod ; 

 u, regulating slide on cataract-rod ; v, exhaust-pipe to 

 condenser ; w, Y-posts for carrying the gear. The 

 steam in the boiler was from 40 Ibs. to 50 Ibs. on the 

 square inch above the atmosphere. 



Lean states that had the pumping engines at work in 

 Cornwall in 1835 remained unimproved since 1814, at 

 which time they had benefited by three years of con- 

 tinuous improvement, a yearly additional expenditure of 

 80,000/. for coal would have been the consequence, and 

 that the first step was Trevithick's expansive steam from 

 the cylindrical tubular boiler, engines using such steam 

 performing a duty three or four fold what Boulton and 

 Watt had ever attained, or perhaps thought possible 

 of attainment. 1 The birth of the idea of using expan- 

 sive steam may in truth be traced back nearly one 

 hundred years to the time of Newcornen's atmospheric 

 engine, and the hope expressed in 1746 of a smaller 

 boiler and more elastic steam 2 was partially realized 

 in the engine and boiler of Trevithick, sen., in Bullan 

 Garden in 1775, followed in 1780 by the competing 



1 See Lean's Historical Statement, p. 154 ; published 1839. 



2 See vol. i., p. 7. 



