The link is hung by a pendulous bar, _g h_, to the end _g_ of the arm _E_, attached to the shaft _A_. This shaft has another upright arm, _F_, which is connected by a rod or bar, _G G′_, to a lever, _H I_, called a reverse lever, whose fulcrum is at _I_. To save room, in the engraving this lever and the cylinder _G_ are drawn nearer to the main axle _S_ than they would be on an engine. The lever is located inside the cab of the locomotive, and is indicated by the numbers 17 17′ in Figure 36 on p. 133, which is a view looking from the tender at the back end of a locomotive. The lever has a trigger (_t_, Fig. 24) which is connected by a rod, _r_, to a latch, _l_, which engages in the notches of the sector _S S′_. This latch holds the lever in any desired position and can be disengaged from the notches by grasping the upper end of the lever and the trigger. It is plain that, by moving the upper end of the reverse lever, the link _a b_ can be raised up or lowered at will. When the link is down, or in the position represented in the engraving, the forward eccentric rod imparts its motion to the block _B_, pin _c_, and thence to the rocker and valve, and the engine will run forward. If, however, the reverse lever is thrown back into the position indicated by the dotted line _J I_, the link would then be raised up so that the end _e_ of the backward-motion rod would be opposite to the block _B_ and pin _c_ and would communicate its motion to the rocker and valve, and the wheels would then be turned backward instead of forward. It will thus be seen how the movement of the reverse lever effects the reversal of the engine. A locomotive is started by admitting steam to the cylinders by means of what is called the "throttle-valve." This is usually placed in the upper part of the boiler at _T_ (Fig. 16). The valve is worked by a lever at _l_, which is also shown at 14, 14′ (Fig. 36). The steam is conveyed to the cylinders by a pipe (_s_, Fig. 16, p. 115). If steam is admitted to the cylinders and the wheels are turned, one of two results must follow: either the locomotive will move backward or forward according to the direction of revolution, or the wheels will slip, as they often do, on the rails. That is, if the resistance of the cars or train is less than the friction or "adhesion" of the wheels on the rails, the engine and train will be moved; if the adhesion is less than the resistance the wheels will turn without moving the train.