38 WATT. 



from impairing the vacuum. The communication could 

 easily be effected by a tube, and the water could be 

 pumped out. This is the first and the grand invention 

 by which he at once saved three-fourths of the fuel, 

 and increased the power one-fourth, thus making every 

 pound of coal consumed produce five times the force 

 formerly obtained from it. But this was not all. He 

 found it expedient to remove the air from the upper 

 part of the cylinder, as it tended to diminish the heat. 

 In effecting this he was, secondly, led to open a com- 

 munication with the boiler, and introduce steam above 

 the piston while it descended, thus making the upper 

 chamber of the cylinder air-tight. The steam thus acted 

 in aiding the descent of the piston, instead of that de- 

 scent being accomplished merely by the atmospheric 

 pressure, ttirdly the counterpoise at the pump-rod 

 was done away, as a mere loss of power, and the pis- 

 ton was now forced upwards by the steam entering to 

 fill the cylinder. These two great additional improve- 

 ments only required a communication to be opened 

 by tubes with the condenser" as well as the boiler, and 

 they gave to the machinery its right to be called a 

 steam-engine ; for it now worked more by steam than 

 by air. The upper chamber was kept air-tight by 

 making the piston-rod work in a socket of tow satu- 

 rated with grease, called the stuffing-box, which also 

 diminished greatly the friction of the rod. 



If Mr. Watt's invention had gone no further than 

 this, we may perceive that it not only increased the 

 power of the fuel fivefold directly, but obtained from 

 the steam as much additional force as could be derived, 

 the limit being only the strength of the materials, 

 within which limit the safety-valve of Papin always 

 enabled the engineer to keep his power. But the 

 three particulars which have been described were not 

 the whole of this great engineer's improvements upon 

 the mechanism of his predecessors. The smooth work- 

 ing of the engine, especially if it be applied to other 



