THE CONQUEST OF NATURE 



different census periods fails to afford a true basis for 

 measuring progress toward larger units during the past 

 ten years. 



"Developments of the past few years in the distribu- 

 tion of power by the use of electric motors have served 

 to accelerate the tendency toward larger steam units and 

 the elimination of small engines in large plants and to 

 change completely the conditions just described. For 

 example : In one of the largest power plants in the world, 

 which is now being installed, all the stokers, blowers, 

 conveyors, and other auxiliary machinery are to be 

 driven by electric motors. Such rapidly changing con- 

 ditions tend to invalidate any comparisons of statis- 

 tical averages deduced from figures for periods even 

 but a few years apart. 



"Comparison of two important industries will il- 

 lustrate the foregoing. The average horse-power 

 of the steam engine used in the cotton mills of the 

 United States in 1890 was 198, and in 1900 it was 300. 



"In the iron and steel industry the average horse- 

 power per engine in 1890 was 171, and in 1900 it was 

 235. In the cotton mills the use of single large units of 

 motive power, with few auxiliary engines of small capac- 

 ity, gives the largest horse-power per engine of any in- 

 dustry; while in the iron and steel industry the average 

 of the motive power proper, although probably larger 

 than in the manufacture of cotton goods, is reduced by 

 the large number of small engines which are used for 

 auxiliary purposes in every iron and steel plant." 



It will be understood that the object of exploding the 

 mixed gases in the oil engine is to produce sudden heat- 



