THE GROWTH OF THE STEAM-ENGINE. 



!37 



vised bis first and his greatest invention the separate condenser. 

 His object in using it was, as be says himself, to keep the cylinder as 

 hot as the steam that entered it. He was therefore the first to appre- 

 hend and to state a problem which the modern engineer is still vainly 

 endeavoring completely to solve. 



Watt was, at this time, twenty-nine years of age. Having taken 

 this first step and made such a radical improvement, the success of 

 the invention was no sooner determined than others followed in 

 rapid succession as consequences of the exigencies arising from the 

 first radical change in the old Newcomen engine. 



But in the working out of the forms and proportions of details in 

 the new engine, even Watt's powerful mind, with its stores of hap- 

 pily-combined scientific and practical information, was occupied for 

 years. 



35. In attaching the separate con- 

 denser, he first tried surface condensa- 

 tion, as in Fig. 14, which is a sketch of 

 his first model ; but this not succeeding 

 well, he substituted the jet. Some pro- 

 vision became at once necessary for 

 preventing the filling of the condenser 

 with water. 



Watt at first intended adopting the 

 same expedient which worked satisfac- 

 torily with the less effective condensa- 

 tion of Newcomen's engine, i. e., lead- 

 ing a pipe from the condenser to a depth 

 greater than the height of the column of 

 water which could be counterbalanced 



by the pressure of the atmosphere ; but he subsequently employed the 

 air-pump, which relieves the condenser, not only of the water, but of 

 the air which also usually collects in considerable volume, and vitiates 

 the vacuum. 



He next substituted oil and tallow for the water previously used 

 in lubrication of the piston and keeping it steam-tight, in order to 

 avoid the cooling of the cylinder incident to the use of water. 



Still another cause of refrigeration of the cylinder, and consequent 

 waste of power in its operation, was seen to be the entrance of the 

 atmosphere, which came in at the top and followed the piston down 

 the cylinder at each stroke. 



This the inventor concluded to prevent by covering the top of the 

 cylinder, and allowing the piston-rod to play through a " stuffing-box," 

 which device had I0112; been known to mechanics. He accordingly not 

 only covered the top, but surrounded the whole cylinder with an 

 external casing or " steam-jacket," and allowed the steam from the 

 boiler to pass around the steam-cylinder and to press upon the upper 



Fig. 14. Watt's First Model, 1765. 



