72 
lieport of the Juihjes on the 
solid ; it is canied iii two beaviugs, the one near the fly-wheel adjustable up 
and down, that near the cylinder adjustable sideways. 
The bearings are supported on cast-iron brackets, bolted onto the barrel of 
the boiler. 
The guide-bars, four in number, are of cast iron ; the guide-blocks aje also of 
cast iron. The adjustment for wear is made by letting the bars together. 
There are the usual two eccentrics, one for the main slide, and the other for 
the expansion. 
The variation of the expansion is due to the action of the governor, which 
works the slide stalk by means of a toothed sector, the position of which, in 
relation to the governor, can be altered. The motion of the sector is given to 
a pinion on the expansion-slide stalk, and in this way the engine is regulated 
bj' the variation iu the expansion. There is also a regulation from the same 
governor by means of a throttle-valve apparatus, which is of a peculiar 
construction. 
The valve has a coil spring, in the nature of a clock-spring, attached to it, 
which always tends to keep it fully open. The arm on the spindle of the valve 
carries a pin, which is worked by the governor through a rod, terminating in a 
Fig. G. — Indicator-diagram of Tlie Reading Iron WorJcs Co.'s Portahle 
Steam-Engine, No. 2927 (No. 4 diagram, 48 lbs. spring). 
long slot, in which the pin lies. The governor makes far more than the 
necessary traverse for the mere moving of the throttle-valve from wide open to 
close shut, so that a small portion of the whole motion of the governor would 
suffice to effect the total motion of the valve. Advantage is taken of this 
construction, and in the following manner. Assume that it is intended to run 
the engine at such a speed that the governor balls will be so far out as to 
leave only a further 3-inch of motion in the collar of the governor, then the 
position of the slot is so adjusted (by means of a right and left-handed screw) 
that.when the governor balls are in the position intended the valve is wide 
open, and there is no wire-drawing whatever of the steam ; but, assuming the 
engine to go more quickly, and the balls to open out further, thej' will begin 
to close the valve, and if they went out to their extreme distance they would 
close it entirely. By this arrangement the engine can be set within con- 
siderable limits, to run with the full-open throttle, and yet to give the 
governor such control as will close the valve. 
There is a further adjustment of the expansion ; this is done by hand when 
the engine is standing, and consists in shifting the position of the expansion 
