REGULATION OF STEAM.

105

machine, for undoubtedly all motors, especially those travellingat such high speed as the locomotive-engine, should be as simpleas possible.

The means adopted for keeping the link in position, to suit thegrade of expansion that is required, is effected by placing a lifting armon the weigh-shaft that crosses the engine, having a rod attached, pass-ing along to the starting platform, to which is fitted a quadrant andreversing lever for taking the long rod, connected to the lifting arms,on the weigh-shaft. The reversing handle has a catch and quad-rant having a number of notches cut on its periphery, so by pullingthe reversing handle the link is raised; the catch is then released,and being fitted with a spring, instantly drops into any one of thenotches, thus holding up the link. As the weight of the links androds is considerable, they are balanced with a weight fitted to anarm on the weigh-shaft; thus the power required to move the linksand rods is equalized very nearly.

Many well-designed link-motions, from imperfections in the modeof Suspension, have failed to give all the requisites necessary for aperfect motion, a free admission and release of the steam being ofthe first importance. The lead or opening of the port by valve atthe commencement of the stroke should be equal, or nearly so, forall grades of expansion, both for the forward and backward move-ment; this being the case, the release must follow as a matter ofcourse. It is often necessary, when designing a new arrangement,to make a skeleton model, to practically test the best position forsuspending the link, as the latter becomes very sensitive should thispoint not be duly attended to. However, by carefully laying outthe valve-gear on paper, drawing it accurately to scale, testing bydelineation the various positions, the proper point of Suspension canbe arrived at without the aid of the model. The point of Suspensionof the link itself is midway between the eccentric-rod ends, bn thearc described by the radius line, or nearly so, and on which thesuspension-rod should vibrate equally forward and backward. Somelinks are suspended from the bottom, on the pin, for the backgoingeccentric-rod; and instead of the valve-rod being guided as in theformer examples, a long rod is jointed to the valve-spindle, andsupported at the link end with a vertical oscillating arm, having adouble joint and pin direct, passing through the long rod, the link-block working in a double joint on the end of the rod, the blockmoves slightly up and down, following the arc of the oscillating