THE ENGINE PROPER. 59 



much below their actual or brake horse-power, which is a 

 condition of affairs to be regretted. However, it would be 

 a difficult matter to change this at the present time and to. 

 educate the users of these engines to comprehend the true 

 size of the unit "horse-power," since the practice of under- 

 rating has existed since engines for driving threshing ma- 

 chines were first built, and it has grown up with the business. 

 If we look into history and causes, we find that the early 

 method of driving threshing machines was by horse-power, 

 and when engines were first used for threshing, a ten horse- 

 power engine was supposed to supply about the same amount 

 of power as a lever-power driven by ten horses. From the 

 time of those early engines, to the present, the competition 

 of different manufacturers, all endeavoring to furnish the 

 most powerful engine of a given rating, and the raising of 

 the steam pressure from 60 to 130 or even 160 pounds, 

 (which was done without reducing the size of the cylinder 

 of a given rating), has caused engines of this class to be 

 more and more under-rated. Most threshing engines, now 

 built in the United States, will easily develop from two to 

 three times their rated horse-power, and the relation which 

 .the rated horse-power bears to the actual size of the engine 

 varies so greatly, that, in reality, the "rated horse-power" 

 gives only a very indefinite idea of the actual size of an 

 engine. / There are reasons why it is preferable to indicate 

 the size of an engine by size of its cylinder, instead of by 

 its rated horse-power ; for example to say, a "Nine by Ten/' 



