568 



THE STEAM-ENGINE. 



be recollected that a reservoir of cold water is placed in the tender which 

 follows the engine, and that the water is driven from this reservoir into the 

 boiler by a forcing pump, which is worked by the engine itself. This pump 

 is so constructed that it will supply as much cold water as is equal to the 

 evaporation, so as to maintain constantly the same quantity of water in the 

 boiler. But it is evident, on the other hand, that the supply of this water has 

 a tendency to check the rate of evaporation, since in being raised to the tem- 

 perature of the water with which it mixes it must absorb a considerable portion 

 of the heat supplied by the fire. With a view to accelerate the production of 

 steam, therefore, in ascending the inclines, the engine man may suspend the 

 action of the forcing pump, and thereby stop the supply of cold water to the 

 boiler ; the evaporation will go on with increased rapidity, and the exhaustion 

 of water produced by it will be repaid by the forcing pump on the next level, 

 or still more effectually on the next descending incline. Indeed the feeding 

 pump may be made to act in descending an incline, if necessary, when the 

 action of the engine itself is suspended, and when the train descends by its 

 own gravity, in which case it will perform the part of a brake upon the de- 

 scending train. 



5. The mechanical connexion between the piston of the cylinder and the 

 points of contact of the working wheels with the road may be so altered, upon 

 arriving at the incline, as to give the piston a greater power over the working 

 wheels. This may be done in an infinite variety of ways, but hitherto no 

 method has been suggested sufficiently simple to be applicable in practice ; 

 and even were any means suggested which would accomplish this, unless the 

 intensity of the impelling power were at the same time increased, it would 

 necessarily follow that the speed of the motion would be diminished in exactly 

 the same proportion as the power of the piston over the working wheels would 

 be increased. Thus, on the inclined plane, which rises fifty-five feet per mile, 

 upon the Liverpool line, the speed would be diminished to nearly one fourth of 

 its amount upon the level. 





THE END. 



