WORKING UP THE HILL.
At the top of the descending grade, the engineer shuts off the steam while the fireman oils the valves: then he puts on a little steam, using a light throttle while the train is increasing in speed, until the base of the ascent is nearly reached, when he gets the throttle full open, letting the engine do its best work in the first notch off the center. By this time the train is swinging along thirty miles an hour, and is well on to the hill before the engine begins to feel its load. Decrease of speed is just becoming perceptible when the valve-travel gets the benefit of another notch, and the engine pulls at its load with renewed vigor. But soon the steepness of the ascent asserts itself in the laboring exhausts; and the reverse-lever is advanced another notch, to prevent the speed from getting below the velocity at which the engine is capable of holding the train on this grade. While the engineer is careful to maintain the speed within the power of his locomotive, he is also watchful not to increase the valve-travel faster than his fire can stand it; for, were he to jerk the lever two or three notches ahead at the beginning of the pull, the chances would be that he would “turn” its fire, or tear it up so badly that the steam would go back on him before he got half a mile farther on. Before the train is safe over the summit, it will probably be necessary to have the engine working down to 18 inches: but the advance to this long valve-travel is made by degrees; each increase being dependent upon, and regulated by, the speed. The quadrant is notched to give the cut-off at 6, 9, 12, 15, 18, and 21 inches. Repeated experiments, carefully watched, have convinced the engineer of this locomotive, that its maximum power is exerted in the 18-inch notch; so he never puts the lever down in the “corner” on a hill. A great many engines act differently, however, showing increased power for every notch advanced. If the cars in the train should prove easy running,—and there are great differences in cars in this respect,—it may not be necessary to hook the engine below 15 inches, or even 12 will suffice for some trains; but this can only be determined by seeing how it holds the speed in the various notches.