APPENDIX C. 



NOTE BY THE EDITOR. 



ALL the preceding data are to-day subject to 

 modification. 



Thus a duty of 150,000,000 ft.-lbs. per 100 Ibs. 

 good coal is to-day attainable, and two thirds that 

 figure is extremely common. With engines of 

 large size the coal-consumption has fallen to one 

 half, sometimes even to one fourth, the figure in 

 the text. 



Hot-air engines are superseded by the gas- 

 engine and the oil-vapor engine ; which even 

 threaten, in the opinion of many engineers, to 

 ultimately displace the steam-engine. 



Compound and other multiple-cylinder engines, 

 with two, three, and even four cylinders in series, 

 are now always employed where fuel is costly. The 

 reason of their success is, in part, that given in 

 Note H; but in only small part. The real cause 

 of their general adoption is the fact that the in- 

 ternal thermal waste by "cylinder-condensation" 

 which in simple engines ordinarily amounts, 

 according to size, to from 25 to 50 per cent, or 



261 



