210 ENGINES FOR SOUTH AMERICA. 



of the llth October, was to correct an error in an order 

 hastily given a month before ; when, to save time, out- 

 line instructions for this complicated work were hurriedly 

 sent to the manufacturer, that a commencement might 

 be made while the more perfect detail drawings were 

 being completed; the first-proposed position of the fly- 

 wheel would prevent the engiiieman from conveniently 

 reaching the four-way cock ; Trevithick therefore sug- 

 gested that the fly-wheel should be moved to the out- 

 side of the house, and a crank placed on the end of the 

 driving shaft in lieu of the crank-pin in an arm of the 

 'fly-wheel. The sketch illustrating this change makes 

 us fully acquainted with the kind of winding high- 

 pressure steam-puffer engines of 8-horse power, with 

 open-top cylinders of 12 inches in diameter and about 

 3 feet 6 inch stroke, sent to Peru in 1814. Steam, of 

 30 Ibs. to the inch above the pressure of the atmo- 

 sphere, was admitted under the bottom of the piston 

 by a cock moved by an eccentric on the fly-wheel shaft ; 

 the gradual closing of the cock reduced the supply of 

 steam when about one-third of the stroke had been 

 made, wholly cutting it off some time before its com- 

 pletion, making it a high-pressure steam expansive 

 engine. The movement of the cock then turned the 

 steam from under the piston into the chimney blast-pipe, 

 and the down-stroke was performed by the weight of 

 the descending piston, made more than usually deep 

 and heavy to prevent the tendency to twist in the 

 cylinder from the angle of the jointed connecting rod, 

 and also by the momentum of the fly-wheel and its 

 balance-weight, moving at a speed of thirty strokes 

 a minute. Its boiler was the Trevithick wrought-iron 

 cylindrical, with internal tube and fire-place, but so 

 arranged that if necessary the fire could be placed in 



