EXPLANATION OF THE PLATES. 
339 
Fig. 10. and 11., parallel motions for steam boat engines, show how the point 
of connexion of the radius rod may be determined by geometrical construction. 
Thus, having determined the three points, H, h, h\ set off h k equal to C h'; join 
C k, and bisect it with the straight line n d, meeting k h d in the point required : 
for since k d = C d, and h k = C h', we have h d — h'd'; and hence when d arrives 
at d', li will coincide with h', and the motion will thus be properly adjusted. 
Fig. 1. may be constructed in this manner. See art. 492. 
Fig. 12. exhibits a simple parallel motion, and is easily constructed geometrically 
by finding C, the centre of a circle, passing through the three points D D' D''. 
Fig. 13. shows how a pump rod may be attached to this motion. 
PLATE XI. 
This plate represents a plan and elevation of an atmospheric engine for raising 
water from a mine. The beam is supported by a frame of cast iron, designed so 
that it may be taken apart when it is necessary to move the engine to another 
mine, (art. 578.) The steam comes from the boiler by the steam pipe S, and is 
admitted to the cylinder C by a sliding piston in B, (see Fig. 2. Plate vi.) and 
then the piston in the cylinder C rises to the top of the stroke, and the piston rod 
forces the end / of the beam up with it; as the beam rises, it draws the rod F G 
with it, which near the end of the stroke moves the sliding frame H, (art. 483.) 
and by the rod O the slide in B, so as to shut the steam off, and open the passage 
to the air pump A : into the passage a jet of water plays at I. The piston then 
begins to descend by the pressure of the atmosphere and raises the pump rods, and 
at the end of the stroke the part F of the rod F G moves the slide, and shuts the 
passage to the air pump, and opens that for the steam. See Plate vi. Fig. 1. 
The parallel motion 1 is guided by the radius rod cd attached to the frame, (art. 
491. and 495.) and by connecting the rods h i: the same rod does for both ends 
of the beam. The sliding frame H is supported by a cross bar beneath H, 
and another at K, and the slide may be moved by hand by the lever M. Cold 
water for injection is supplied by the pump E, and water is raised from the hot 
well by the pump D, and passes to the boiler by the pipe Q, with a small branch 
pipe at P, to give water to the top of the piston. See art. 400—405. 
1 In the parallel motion apparatus, shown in Fig. 1., the vibration of the beam is not bisected. 
See p. 233, Note.