the open sky.  The pace is increasing, the steady beat of the engine tells more distinctly on the ear than in the daytime; the foot-plate is lit up by the glare from the fire-door; but still there is nothing to be seen ahead but the impenetrable night.  Looking back, however, the scene is very different.  The tender and guard’s van glow in the light thrown by the fire, trees and houses by the side of the track stand out sharply for a moment and are then lost to sight, the light from the carriage windows produces the effect of the wake of a ship seen from the stern.  Gradually the clouds have rolled away, leaving the sky clear.  The moon is seen fitfully through the whirling steam; the surrounding country is visible for miles round.  The effect produced is unspeakably beautiful.  In the mean time let us turn our attention to the working of the engine.  In the first place, let us take note that, although the engine we are now on, and that which took us from London, belong to the same type, their performances are somewhat different.  No two engines ever resemble each other, no matter how carefully they may have been built from the same plan, neither do any two drivers manage their engines precisely in the same way.  We have in this instance an excellent opportunity of comparing two different methods of driving.  It is the driver’s principal object to get the required amount of work out of his engine with the smallest possible expenditure of coal and water.  To obtain this result the steam must be worked expansively, which is done by placing the valve gear in such a position by means of the lever that the supply of steam to the cylinders is cut off, as we have stated at the beginning of this article, before the piston has accomplished its full stroke.  There are two ways of controlling the speed of an engine worked, as all locomotives are worked now, expansively.  You may keep the regulator wide open, so that there is always a full supply of steam on its way to the cylinders, in which case you increase or diminish the speed by using the steam more or less expansively through the agency of the lever.  Or you may work with the same amount of expansion throughout the journey, and have command of the engine by constantly changing the position of the regulator.  There is no doubt that the men who employ the latter method save something by it, although this would hardly seem to be the opinion of the driver who is bringing us rapidly nearer to London, for unlike the driver whom we accompanied on the daylight journey, his hand is not often on the regulator.  As we rush on past countless signals, punctual to the minute, yet always having ample time to slacken speed before we come to the places where the different colored lights cluster thickest, we are reminded once more how much is required of an express engine-man besides a thorough acquaintance with the machinery he has to control.  Traveling at night at a great speed, he must know every inch of the road by heart—­where an incline begins and where