180 OF THE CONSTRUCTION OF [SECT. v. 



the p= P art of the stroke, the cylinder being 12 inches in diameter, the velocity 



160 feet per minute, and the whole force of the steam in the boiler 120 inches of 

 mercury, or 46 Ibs. per circular inch, 



First. 2-3 x log. 1*5 = 0-405 

 Add 1 1- 



Divide by 1-5) 1-405 



0-936 

 Subtract 0-4 the friction and loss. 



0-536 

 Multiply by 46 the pressure of the steam. 



24-656 

 Subtract 11-55 the resistance of the atmosphere. 



And 13-106 Ibs. = the mean effective pressure on each 

 circular inch of the piston. 



Also 12x12= 144 the square of the diameter. 

 Multiply by 160 the velocity, 



23040 

 and again by 13-1 the mean pressure. 



Then 301824 Ibs. = weight raised 1 foot per minute. 

 And m^ =9-15 horse power. 



379. When the steam is cut off at the part of the stroke, the quantity of 



steam consumed in cubic feet per minute will be found by multiplying the area of 

 the cylinder in feet by the velocity in feet per minute, increased by one-tenth, and 

 dividing the product by n. If this result be divided by the volume which a cubic 

 foot of water occupies when in the state of steam of the force in the boiler, (see art. 

 121. or tables,) the quotient will be the quantity of water required per minute, and 

 the equivalent quantity of fuel will be found by art. 190. The actual supply of 

 water, and the power of the boiler should be n times that quantity ; the engine will 

 then either work at full pressure or expansively, as occasion may require. 



380. In an expansive engine the moving force varies from full pressure to 



