408 STEPHENSON'S PATENT 



requiring therefore a construction affording the means of generating steam very 

 rapidly, or having a great evaporating power, in order to supply the steam in 

 sufficient quantity and of the required pressure. The whole engine has to be very 

 strongly and firmly made and framed together, to enable it to resist the violent strains 

 and shocks produced by the rapid motion of so heavy a mass even upon the com- 

 paratively smooth surface of the rails, and also to meet the accidents to which it is 

 liable, and which are generally ve^ serious. 



The construction of these engines has undergone very great and extensive improve- 

 ment during the last few years, and they have not long arrived at their present 

 state of perfection ; those made before the last ten years were greatly inferior, having 

 not more than a fourteenth of the power of the present ones. 



The engine here described, and shewn in the engravings, contains the latest 

 improvements, and is similar in construction to most of those used on railways in 

 England and on the Continent. 



DESCRIPTION OF THE ENGINE. 



Plate LXXXIX. is a side elevation of the engine and tender. The engraving is 

 highly shaded to show more fully their general appearance. 



Plate XC. a longitudinal section through the centre of the engine and tender, 

 showing their internal construction ; the section below the boiler being taken through 

 the right hand cylinder and crank. 



Plate XCI. Fig. 1, is a plan of the engine #nd tender ; the plan of the engine is 

 taken just below the boiler, in order to show the machinery beneath it, and at the 

 left cylinder the plan is taken a little lower down, showing a section of the steam 

 chest and more of the machinery ; figs. 2, 3, and 4 are detached views of the 

 working gear for the slide valves ; figs. 2 and 3 being side elevations, showing the 

 working gear in different positions, to explain their action ; and fig. 4 a back eleva- 

 tion, showing it in the same position as figs. 1 and 3. The plan of the tender is 

 taken at the top. 



Plate XCII. contains an elevation of each end of the engine, and a cross section 

 through each of the end portions. 



The plates are all drawn to a scale of three quarters of an inch to a foot, or one- 

 sixteenth of the real size, and the same letters of reference are used to denote the 

 same parts in each of the figures. 



The different parts of the engine are shown in detail on a larger scale in the wood 

 cuts accompanying the descriptions, according to the size or importance of the parts. 



The construction and object of the different parts of the engine will be explained 

 in succession, together with the wear to which they are subject, the improve- 



