208 



OF THE REGULATION AND 



[SECT. vin. 



O being attached to any convenient part of the parallel motion of the engine, so 

 as to cause the board K to traverse a space of about fourteen inches and a half 

 during each half stroke of the engine. 



Operation. By opening the stop cock B, a direct communication is made 

 between the cylinder of the steam engine and the cylinder of the indicator. When 

 the force of the steam in the cylinder is greater than the pressure of the atmosphere, 

 the piston F will rise ; when the force of steam is less than atmospheric pressure, 

 it will sink. The indicator will consequently rise when the upper steam valve 

 opens, and will be at a height proportional to the force of the steam in the cylinder 

 during the stroke of the engine ; and when the eduction valve opens, it will sink, 

 and by the rapidity and quantity of its descent denote the state of the vapour in 

 the condenser. During the motion of the piston F, the sliding-board will move 

 horizontally, and the pencil in the socket in L will trace on the board K, or on 

 a paper on its surface, a figure, P Q R S, resembling those shown on an enlarged 

 scale in the annexed figures. Of this figure, P Q is described during the descent 



FIG. 23. 



of the steam piston ; at Q the condensation takes place, and the indicator is forced 

 down by the pressure of the atmosphere, till it is balanced by the resistance of the 

 spring and the vapour in the cylinder. While the engine makes the ascending- 

 part of the stroke, the line R S is described ; and the line S P is described during 

 a fresh admission of steam by the upper valve. 



