434 
STEPHENSON’S PATENT 
each end, a branch from the waste port being brought up alongside of them corre 
sponding in size and distance with the present one, and a separate slide placed over 
each port. The action of the steam in this arrangement was exactly the same as in 
the present one, but the quantity of steam wasted in the ports was much diminished. 
Double slides were used in several of the first locomotives, but they have since been 
abandoned; as the quantity of steam contained in the ports is but small compared 
with the contents of the cylinder, and the arrangement added considerably to the 
friction and the complexity of the machine. However, in all stationary engines, ex 
cept some of the smallest, double slides are used, but they are generally of a different 
construction and made together in one piece. 
Cross-heads and Guides.—The outer end of the piston rod Y is attached to 
the cross head Z, (Plates XC., and XCI.,) shewn on a large scale in figs. 17, 18, 
and 19, which are drawn three times larger than the engraving, or to a scale of 2^ 
Fig. 17. Fig. 19. 
inches to a foot. Fig. 17, is a plan; one side being shewn broken off, as it is exactly 
like the other side; fig. 18, is a longitudinal section through the centre; and fig- 
19, a cross section shown complete on both sides. The end of the piston-rod A A 
is turned down smaller, and fitted into the wrought iron socket B JB by the key or 
cotter and gib C and D ; the gib D being tapered like the key, making their outer 
edges parallel. Two arms, E E, project from the end of the socket B, parallel to