ENG 
communicates with F, but acts through G 
upon the lower part of the piston H, and 
raises it; while the contents of the great 
cylinder above that piston are driven out 
through F, and pass through the opening at 
D into R. It may be observed, that the 
column which acts against the piston is as- 
sisted by the pressure of the atmosphere, 
rendered active by the column of water 
hanging in R, to which that assisting pres- 
sure is equivalent, as has already been no- 
ticed. When the piston has ascended 
through a certain length, another slide or 
block upon the pit-rod (not seen) applies 
against the tail, K, of the tumbler, which it 
raises and again oversets, producing once 
more the position of the plugs, D E, here 
delineated, and the consequent descent of 
the great piston, H, as before described. 
The descent produced the former effect on 
the tumbler and plugs, and in this manner 
it is evident that the alternations will go on 
without limit, or until the manager shall 
think fit to place the tumbler and plugs, 
D E, in the positions of rest, namely, so as 
to stop the passages, F and G. The length 
of the stroke may be varied by altering the 
positions of the pieces, I, and the other 
lower down, which will shorten the stroke, 
the nearer they are together; as in that 
case they will sooner alternate upon the 
tail, K. As the sudden stoppage of the 
descent of the column, AB, at the instant 
when the two plugs were both in the water- 
way might jar and shake the apparatus, those 
plugs are made half an inch shorter than 
the depth of the side holes, so that in that 
case the water can escape directly through 
both the small cylinders to R. This gives 
a moment of time for the generation of the 
contrary motion in the piston, and the water 
in G G G, and greatly deadens the concus- 
sion which niight else be produced. See 
Steam Engine. 
Some former attempts to make pressure 
engines upon the principle of the steam-en- 
gine have failed ; because water pot being 
elastic, could not be made to carry the pis- 
tpn onwards a little, so as completely to 
shut one set of valves and open another ; 
in the present judicious construction the 
tumbler performs the office of the expansive 
force of steam at the end of the stroke. 
Engine for driving piles, used at build- 
ing Westminster bridge, is constructed as 
follows : A, (Plate V. Miscel. fig. 3.) is the 
great shaft, on which are the great wheel and 
drum : B, the great wheel with cogs, that 
turns a trundle head with a fly, to prevent 
ENG 
the horse’s falling when the ram is dis- 
charged; C, the drum on which the great 
rope is wound ; D, the follower (with a rol- 
ler at one corner) in which are contained 
the tongs, to take hold of the ram, and are 
fastened to the other end of the great rope 
which passes over the pulley, near the up- 
per end of the guides between which the 
ram falls; E, the inclined planes, which 
serve to open the tongs, and discharge the 
ram ; F, the spiral barrel that is fixed to the 
drum, on which is wound a rope with a 
counterpoise, to hinder the follower from 
accelerating, when it falls down to take up 
the ram ; G, the great bolt which locks the 
drum to the great wheel ; H, the small le- 
vel-, which has a weight fixed at one end, 
passes through the great shaft below the 
great wheel, and always tends to push the 
great bolt upwards, and lock the drum to 
the great wheel; I, the forcing bar, which 
passes through the hollow axis of the great 
shaft, bears upon the small lever, and has 
near the upper end a catch by which the 
crooked lever keeps it down ; K, the great 
lever, which presses down the forcing bar, 
and discharges the great bolt at the time 
the long end is lifted up by the follower ; 
L, the crooked lever, one end of which has a 
roller, that is pressed upon by the great 
rope, the other end bears upon the catch of 
the forcing bar during the time the follower 
is descending ; M, the spring that presses 
against the crooked lever, and discharges it 
from the catch of the forcing bar as soon as 
the great rope slackens and gives liberty to 
the small lever to push up the bolt. 
By the horse’s going round, the great 
rope is wound about the drum, and the 
ram is drawn up, till the tongs come be- 
tween the inclined planes, where they are 
opened, and the ram is discharged. 
Immediately after the ram is discharged, 
the roller, which is at one end of the fol- 
lower, takes hold of the rope that is fast- 
ened to the long end of the great lever, and 
lifts it up ; the other end presses down the 
forcing bar, unlocks the drum, and the fol- 
lower comes down by its own weight. 
As soon as the follower touches the ram, 
the great rope slackens, and the spring, M, 
discharges the crooked lever from the catch 
of the forcing bar, and gives liberty to the 
small lever to push up the great bolt, and 
to lock the drum to the great wheel, and 
the ram is drawn up again as before. 
ENGINEER, in the military art, an 
able, expert man, who by a perfect know- 
ledge in mathematics, delineates upon pa;-. 
