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.