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. 1 7, 1 8, 

 and 1 9, which are drawn three times larger than the engraving, or to a scale of 2^ 



FIG. 17. FIG. 19. 



Fie. 18. 



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- 

 1 9, 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 B 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 



