THE ENGINE PROPER 83 



per cent., we have 47 brake horse-power as the result. 

 In applying the above formula, several of the same figures 

 always occur, and we may combine these in order to make 

 our formula as simple as possible. When we have done 

 this, we have it in the following form : 



PxLxDxDxNxl8_p p 



10,000,000 

 in which P = boiler pressure in pounds per sq. inch. 



L = length of stroke in inches. 



D = cylinder bore in inches. 



N = number of revolutions. 



This may be stated in the form of a rule which can 

 be readily applied by any one. This rule is as follows : 



Multiply together the boiler-pressure, the length of 

 the stroke in inches, the cylinder bore in inches, again the 

 bore in inches, and this product -finally by 18. Divide the 

 result by 10,000,000 (which is simply pointing off seven 

 places'), and the quotient is the brake horse-power. 



The following illustrates the application of this rule 

 to the Case forty-five horse engine : 



130 = boiler pressure. 



10 = length of stroke in inches. 

 1,300 



9 = cylinder bore in inches. 



11,700 



9 cylinder bore in inches. 



105,300 



250 = revolutions per minute. 



5,265,000 

 21.060.000 

 26,320,000 



18 = the constant. 



210,560.000 

 263.200.000 



473,760,000 



