Processes in the Useful Arts, 171 



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. 10, having completed 

 half its stroke, when piston 1, Fig. 9, 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..9, has performed one-fourth 

 its stroke, that the piston 1, Fig. 10, has moved from c to 6, performing 

 seven-sixteenths of its stroke in the same time. The mean in each quar- 

 ter, from c to e, Fig. 10, being 150lbs. the amount of pressure to be added 

 to the first quarter of the stroke of the piston. Fig. 9, (which was 400lbs.) 

 is 275lbs. producing an available power of 675lbs. at this part of the stroke. 

 The piston. Fig. 10, now moves but two-sixteenths of its stroke from 6 toe, 

 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 (within a fraction) with 

 the same velocity of the piston. The piston. Fig. 10, in moving from 6 to e, 

 gives a power of 25lbs. being the last of the expansion which ends at lOOlbs. 

 per inch. The piston, Fig. 10, in moving from f to 8, being the beginning 

 of the stroke, gives a power of lOOlbs. ; thus a power of 125lbs. will be 

 acting in the piston 1, Fig. 9, while moving from b to d, giving a power 

 of 4.75lbs. to which add 125, will show a power of GOOlbs. at this part of 

 the stroke. The piston 1, Fig 9, now descends from d to e, being the last 

 quarter of the stroke, giving 125lbs. of power to act with the piston 1, Fig. 

 10, while moving from 8 to h, giving a power of 600lbs. ; add to this the 

 125lbs. and it will give a power of 725lbs at this part of the stroke. The 

 piston 1, Fig. 9, now begins its stroke of 400lbs. per inch at f, and con- 

 tinues to g with the same power, while piston 1, Fig. 10, moves from h to 

 12, giving a power of SOOlbs. to be added to the 400lbs., obtained at the 

 first quarter of the stroke of the piston 1, Fig. 9, at f and g, producing at 

 this part of the stroke 700lbs. of power. The piston 1, Fig. 9, now moves 

 from g to i, giving a power of 475, while the piston 1, Fig. 10, moves from 

 12 to k and a to 2, giving a power of 125 ; which add to 475, gives a 

 power of 600 at this part of the stroke. The piston 1, Fig. 9, now moves 

 from i to 1, being the last quarter of the stroke, giving a power of 125lbs., 

 while the piston, Fig. 10, moves from 2 to c, producing a power of 600 ; to 

 which add 125lbs. will make 725lbs. at this part of the stroke. We have, 

 therefore. 



Fig, 9, AA, 400 Fig. 9, BB, 475 Fig. 9, CC, 125 



Fig. 10, AA, 275 Fig. 10, BB, 125 Fig. 10, CC, 600 



675 600 725 



Fig. 9, DD, 400 Fig. 9, EE, 475 Fig. 9, FF, 125 



Fig. 10, DD, 275 Fig. 10, EE, 125 Fig. 10, FF, 600 



675 : 600 725 



By this arrangement, it will be seen that a compensation is obtained. 



