406 EXPLANATION OF THE PLATES. 



piston up again, and transfer the steam from the top to the bottom of the cylinder, 

 when the lower tappet shuts the equilibrium valve, and the action of its catch 

 releases the catch of the steam and eduction valves, thereby admitting of their 

 opening as before, and being the means of making the motion of the engine con- 

 tinuous. 



The general construction of this engine is so analogous to that applied for pumping 

 engines in water works of late years, that we think it necessary only to direct 

 attention to those parts which are particularly striking. 



Viewed merely as a machine, it is an admirable specimen of workmanship. The 

 beam, and many of the parts, exhibit great strength, and are fully equal to the 

 application of the expansive principle of working, should the adoption of it at a 

 future period be determined upon. The castings throughout are of a superior 

 description, and the fittings and bright work exhibit an attention to detail that 

 cannot fail to attract the notice of the mechanic ; he will perceive that the lathe 

 and planing machine have lent their aid to all the bearing surfaces, and that every 

 care has been taken to ensure solidity of construction. 



The boilers are of 'wrought iron, upon the marine principle, securely stayed, and 

 fitted with safety valves, feed pipes, and the usual apparatus, with the addition of 

 whistle pipes, that old but effectual mode of making known the deficiency of water 

 in the boilers. 



Arrangements have been made to cover the boilers, steam pipes, and cylinder 

 with non-conducting substances, as soon as the works are proved. 



The structure of this engine admits of its being worked to the various altitudes 

 required for street supplies, the chief means of regulation being the expansion 

 tappet and safety catch, the latter acting when the length of the stroke exceeds 

 the proper limit. The counterweight for adjusting the engine moves between 

 guide strips inside the beam ; it is worked by a long screw, which (the cross 

 handle being moveable) admits of the whole range of the weight between the 

 catch pins when the engine is at work. 



The main pump and clack seats are fixed in a very substantial manner ; they are 

 supported by four strong iron beams, (through which very large holding down bolts 

 pass,) and they are steadied by iron plates fixed above and forced against the masonry. 

 The supporting beams are fixed within four feet of the bottom of the working barrel, 

 and the masses of stone above them are considerable. 



The pump clacks are of gun-metal, fitted with wrought iron plates leathered ; these 

 are of large dimensions compared with the working barrel, and they are fixed in 

 separate chambered seatings and held fast by distinct rods pressed down by set 

 screws. 



