36 CONTEMPORARY SCIENCE 



that steam pressures were practically limited to a few 

 pounds above atmospheric pressure. The cylinders and 

 pistons of his engines were not constructed with the fa- 

 cility and accuracy to which we are now accustomed, and 

 chiefly for these reasons expansion ratios of from two 

 to threefold were the usual practice. Watt had given to 

 the world an engine which consumed from five to seven 

 pounds of coal per horse-power hour, or one-quarter of 

 the fuel previously used by any engine. With this con- 

 sumption of fuel its field under the conditions prevailing 

 at the time was practically unlimited. What need was 

 there, therefore, for commercial reasons, to endeavor 

 still further to improve the engine at the risk of encounter- 

 ing fresh difficulties and greater commercial embarrass- 

 ments? The course was rather for him and his partners 

 to devote all their energy to extend the adoption of the 

 engine as it stood, and this they did, and to the Watt 

 engine, consuming from five to seven pounds of coal per 

 horse-power, mankind owes the greatest permanent ad- 

 vances in material welfare recorded in history. 



With secondary modifications, it was the prime mover 

 in most general use for eighty years i.e., till the middle 

 of last century. It remained for others to carry the ex- 

 pansion of steam still further in the compound, triple, 

 and, lastly, in the quadruple expansion engine, which is 

 the most economical reciprocating engine of to-day. 



Watt had considered the practicability of the turbine. 

 He writes to his partner, Boulton, in 1784: "The whole 

 success of the machine depends on the possibility of 

 prodigious velocities. In short, without God makes it 

 possible for things to move them one thousand feet per 

 second, it cannot do us much harm." The advance in 

 tools of precision, and a clearer knowledge of the dynam- 

 ics of rotating bodies, have now made the speeds men- 

 tioned by Watt feasible, and indeed common, everyday 

 practice. 



Turbines. The turbine of to-day carries the expansion 



