THE STEAM-ENGINE. 



243 



ing of the float, S, and opened whenever the float sinks 

 from low water. M, barometer s:aus;e, to show the 



Fig. 203, 



Boiler of Steam-ensine. 



pressure of the steam ; w, weight on the lever, e b, for 

 holding down the safety-valve : this lever being grad- 

 uated like a steelyard, the force of the steam may he 

 accurately weighed. U is a valve opening downward, 

 to prevent the boiler being crushed by atmospheric 

 pressure, by allowing the air to pass in whenever the 

 steam happens to decline. Two tubes with stop-cocks, 

 c and d, one just below the water-level and the other 

 just above it, serve to show, by opening the cocks, 

 whether the water is too high or too low. 



The working part of the engine is represented in the 

 figure on the following page {Fig. 204). The steam 

 enters by the pipe, s, from the boiler on the other side 

 of the brick wall, as shown in Fig-. 203. The steam 



