In all these the absence of wire-drawing may be specially noted by the full line at the top of the diagram, showing the admission of steam—­this fullness arising from the rapid and full opening of the port for admission.

Passing now to the other great type of engines, those covered under the general designation of marine engines, this gear has been applied to nearly 40,000 H.P. indicated, built and building, and to all classes and sizes, from the launch engine with cylinders 8 inches by 9 inches, running at 600 to 700 revolutions per minute, up to engines for the largest class of war ships, such as her Britannic Majesty’s steel cruiser Amphion, of 5,000 H.P., with cylinders in duplicate of 46 inches and 86 inches diameter, and 3 feet 3 inches stroke, running 100 revolutions per minute.  An examination of the indicator diagrams taken from these engines shows that no wire-drawing takes place, and that, though the expansion is carried to a point beyond the ordinary requirements, the compression is but slightly increased.  In all the diagrams taken from this valve motion there is seen the clear, full upper line showing an abundant admission of steam without any wire-drawing, and also the distinctly marked points where “cut-off” or “suppression” and where “release” takes place, showing the rapid action of the valves at those points.

It is well known to engineers that to obtain the maximum advantage out of compounding, it is necessary to cut off in the low pressure cylinder at a point corresponding to the relation between the low and the high, and that point should be unaltered, whereas the point of cut-off in the high may at the same time be varied to suit the work to be done.

In an ordinary link motion engine (where both links are connected to the same weigh shaft), when linking up the high pressure cylinder to cut-off short, the same change is necessarily made in the low.  By the use of the Joy gear, cut-off valves may be fitted to both cylinders, that for the low pressure being fixed at the constant position required by the proportion of the cylinders, while that on the high is adjustable; of course, in this case, the position of the quadrants must be only changed for reversing.  In arranging the independent cut-off on the Joy gear, it is only necessary to increase the length of the vibrating link beyond the point of attachment for the main valve spindle connection to obtain a point from which motion may be taken to actuate the cut-off valve; even then the cost of the Joy gear for both cylinders is but little more than for a single set of link gear.

This arrangement gives an absolutely perfect distribution of steam for compounding, also equalizes the power developed by both cylinders, and is far more simple and inexpensive than any other gear in existence.

* * * * *

THE STEAM BELL.

[Illustration:  FIG. 1.]