60 Perkins" 1 Steam Engine. 



each quarter, which add to the other two quarters, 400. 300- 

 150. 150. and the whole sum will be 1000,* giving an av- 

 erage pressure of 250 per square inch. It will be seen that, 

 when the stroke is completed, the cylinder will be filled with 

 steam at a pressure of lOOlbs. per inch, which will be the 

 same in quantity as though the steam had begun with a pres- 

 sure of lOOlbs. per inch, and continued all the stroke at that 

 pressure. By using the same quantity of steam expansively, 

 beginning at 400lbs., there is a gain of 150 per cent. If the 

 steam is used at 600lbs. per inch, and cut off at one-eighth of 

 the stroke, 225 per cent, will be the gain. To compensate 

 for the unequal pressure of the steam on the piston, two cyl- 

 inders should be used, particularly for steam boats and pump- 

 ing, where the fly should be dispensed with. With the fol- 

 lowing arrangement, it will be seen, that while one of the 

 pistons is at its greatest power, the other is acting with a di- 

 minished power. 



The piston 1 , fig. 1 , in descending from a to 6, moves in 

 the same time through only half the space through which 

 the crank moves, as will be seen by its path from 1 to 3. A 

 force of 400lbs. is exerted on the square inch (that being the 

 pressure of the steam,) in the first quarter of the stroke: at 

 this point the steam is cut off leaving the other three-fourths 

 of the stroke to act expansively. The piston 1 , fig. 2, hav- 

 ing completed half its stroke, when piston 1, fig. 1, begins 

 its stroke, and consequently a compensation, near enough 

 for all practical purposes, takes place. 



It will be seen, that while the piston 1 , fig. 1 , has perform- 

 ed one-fourth of its stroke, that the piston 1 , fig. 2. has mo- 

 ved from c to 6, performing seven-sixteenths of its stroke in 

 the same time. The mean in each quarter, from c to e, 

 fig. 2, being 150lbs., the amount of pressure to be added to 

 the first quarter of the stroke of the piston, fig. 1 , (which 

 was 400lbs.) is 275lbs., producing an available power of 

 675lbs. at this part of the stroke. The piston, fig. 2, now 

 moves but two-sixteenths of its stroke from 6 to e, and f to 

 8, while the crank moves through two of its divisions, from 

 6 to 8, which would, in another part of its path move (with- 

 in a fraction,) with the same velocity as the piston. The 



* If the steam had continued the whole length of the stroke at 400lbs. 

 per square inch, the sum would have been 1600lbs. consuming four 

 times the steam with the addition of only 60 per cent to the power. 



