and Miscellaneous Implements at Hull. 
G39 
very small holes, separates these two chambers. The water is forced 
through these perforations by the action of the pump in the form of fine spray, 
which, mingling with the 
steam, is made hot and 
flows into the water-tank at 
nearly boiling point. The 
■compressed air in the upper 
chamber makes the flow of 
the water through the per- 
forations constant, and not 
intermittent, with the stroke 
of the pump. It is similar 
in its action to the air- 
chambers used in hydraulic 
rams, but requires no snifile- 
valve, as fresh air is ad- 
mitted every time the engine 
ceases to work. The Judges 
•considered thisa contrivance 
of great value, combining 
simi^licity, lightness, and 
strength with a cheap- 
ness that brings it within 
the reach of all users of 
steam power. Its cost is 
51. 10s., and, with slight 
modifications, it can be 
■easily fitted to any engine 
■or boiler. 
4788. Head, Wrightson, and Co. — This pulley-block or hoist is constructed 
•on a novel and ingenious principle. Although its parts are simple in con- 
struction, and therefore not liable to get out of order, yet at first sight its 
•action seems like a mechanical puzzle, and a full description of the illustra- 
tions given may perhaps be needed to explain the principles of its action. 
Two revolving discs (a and b, Fig. 17) are mounted face to face ujxm a 
shaft (c). The meeting face of each disc is dished out, and the periphery of 
■each dished recess is formed into an internal toothed wheel (Fig. 19, p. 640). 
One disc has a tooth less in number than the other, but both have the 
same pitch diameter, 
"When the discs are mounted on the shaft c, the space formed by the 
meeting of these two recesses is occupied by the pinion d, of smaller pitch 
diameter than the internal disc wheels, a and b. This pinion is mounted 
loose upon an eccentric forged in one with the shaft c, passing through the 
discs, and is carried round by the revolution of the shaft and eccentric. In 
revolving, the pinion rolls round the peripheiy of the internal wheels, and in 
one complete orbit the faces of the two discs move a distance equal to 
the pitch of one of the disc teeth, owing to the gradual displacement of the 
odd tooth. 
A chain-wheel (f and g) is cast on the back of each disc, and from the 
cross head and hook (h), to which the weight to be lifted is attached, two 
■chains pass, one to the right side and one to the left side of either disc chain- 
wheel. 
The loose ends pass over aud are connected at a convenient distance below 
the block, fonning a loop (k), which falls as the weight is raised, and vice 
(versa. 
The eccentric shaft is made to revolve by the spocket-wheel (l) keyed to 
