POWER EMPLOYED IN MANUFACTURES 215 



The tendency toward great operations, which has been 

 such a conspicuous feature of industrial progress during the 

 past ten years, has showed itself strikingly in the use of units 

 of larger capacity in nearly every form of machinery, and 

 nowhere has this tendency been more marked than in the 

 motive power by which the machinery is driven. At the same 

 time there has been an increase in the use of small units, 

 which tends to distort the true tendency in steam engineering 

 in these statistics. For example, a steam plant consisting 

 of one or more units of several thousand horsepower may also 

 embrace a number of small engines of only a few horsepower 

 each, the use of which is necessitated by the magnitude of the 

 plant, for the operation of mechanical stokers, the driving of 

 draft fans, coal and ash conveyors, and other work requiring 

 power in small units. On this account the average horse- 

 power of steam engines in use at 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 distribution 

 of power b}^ the use of electric motors have served to acceler- 

 ate the tendency toward larger steam units and the elimina- 

 tion 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, all the stokers, blowers, con- 

 veyors, and other auxiliary machinery are to be driven by 

 electric motors. Such rapidly changing conditions tend to 

 invalidate any comparisons of statistical averages deduced 

 from figures for periods even but a few years apart. 



Comparison of two important industries will illustrate the 

 foregoing. The average horsepower 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 horsepower 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 capacity, gives the largest horse- 

 power per engine of any industry; 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 



