202  LECTURE XX.

[longitudinal arrangement drawing here]

GENERAL LONGITUDINAL ARRANGEMENT.
DIAGONAL COMPOUND ENGINE AND BOILER.

improvements, such as Joy's valve gear and Alley's flexible main
shaft coupling. As these two improvements or modifications of
them are fast coming into use, we shall illustrate and describe 
them.

<i>Joy's Patent Valve Gear</i> is a clever device, whereby the 
necessary motion of the slide valve, and the facility for reversing
the engine, are effected by a series of links and connections between
the connecting-rod and the valve spindle, thus replacing the
ordinary double eccentrics and Stephenson's link-motion. The
motion obtained by it is a very perfect one for a slide valve, for 
the travel of the valve is made quick on opening and oh shutting off
steam to the cylinder, and slow when the steam is expanding and
exhausting. This is effected without any undue lead or com-