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HORSE POWER. 



The power of a steam-engine is estimated by the following 



RULE. Divide the continued product of the area of the 



piston in inches, the mean pressure per square inch in 



pounds, the length of the stroke in feet, and the number of 



strokes per minute by 33,000. 



EXAMPLE. The area of the piston of a steam-engine is 40 

 inches, the pressure is 60 Ibs. per square inch, the length of 

 the stroke is 3 feet, and it makes 30 strokes per minute. 

 What is the horse-power ? 



OPERATION. (40 x 60 x 3 x 30) -7- 33,000 =<o% horse-power 

 (nearly). 



Water-wheels lose from 10 to 50 per cent, of the power, and 

 the actual power of the steam-engine is less than that indi- 

 cated by the horse-power, owing to a loss by friction, the 

 amount of which depends upon the arrangement of the en- 

 gine and the perfection of the workmanship. 



TABLE, showing the labor one horse is able to perform at 

 different rates of speed on canals, railroads, and turnpikes. 

 Drawing force, 83-J Ibs. 



