ENGINE. 
have been lately erected in different parts 
of the country. The principle now advert- 
ed to was adopted in some machinery exe- 
cuted in France about 1731, and was likewise 
adopted in Cornwall more than forty years 
ago; but the pressure engine, of which we 
are about to give a particular description, 
is the invention of Mr. R. Trevithick, who 
probably was not aware that any thing at 
all similar had been attempted before. This 
engine, a section of which on a scale of |d 
of an inch to a foot is shewn in PlatePressure- 
Engines, one was erected about eight years 
ago at the Druid copper mine, in the parish of 
Illogan, nearTruro. A B, represents a pipe 
six inches in diameter, through which water 
descends from the head to the place of its 
delivery to run off by an adit at S, through 
a fall of 34 fathoms in the whole ; that is to 
say, in a close pipe down the slope of a hill 
200 fathoms long, with 26 fathoms fall ; then 
perpendicularly six fathoms, till it arrives at 
B, and thence through the engine from B to 
S two fathoms ; at the turn, B, the water 
enters into a chamber, C, the lower part of 
which terminates in two brass cylinders, 
four inches in diameter ; in which two plugs 
or pistons of lead, D and E, are capable of 
moving up and down by their piston rods, 
which pass through a close packing above, 
and are attached to the extremities of a 
chain leading over and properly attached to 
the wheel, Q, so that it cannot slip. 
The leaden pieces, D and E, are cast in 
their places, and have no packing whatever. 
They move very easily ; and if at any time 
they should become loose, they may be 
spread out by a few blows with a proper 
instrument, without taking them out of their 
place. On the side of the two brass cylin- 
ders, in which D and E move, there are 
square holes communicating towards, G, 
with a horizontal trunk, or square pipe, four 
inches wide, and three inches deep. All 
the other pipes, G, G, and R, are six inches 
in diameter, except the principal cylinder 
wherein the piston, H, moves; and this cy- 
linder is ten inches in diameter, and admits 
a nine foot stroke. 
The piston rod works through a stuffing- 
box above, and is attached to, M N, which 
is the pit rod, or a perpendicular piece di- 
vided into two, so as to allow its alternate 
motion up and down, and leave a space be- 
tween, without touching the fixed appara- 
tus, or great cylinder. The pit rod is pro- 
longed down in the mine, where it is em- 
ployed to work the pump ; or if the engine 
was applied to mill-work, or any other use, 
this rod. would be the communication of the 
first mover. K L, is a tumbler, or tumbling 
bob, capable of being moved on the gud- 
geons, V, from its present position to ano- 
ther, in which the weight, L, shall hang over 
with the same inclination on the opposite 
side of the perpendicular, and consequently 
the end, K, will then be as much depressed 
as it is now elevated. 
The pipe, RS, has its lower end immersed 
in a cistern, by which means it delivers its 
water without the possibility of the external 
air introducing itself ; so that it constitutes 
a Torricellian column, or water barometer, 
and renders the whole column from A to S 
effectual, as we shall see in our view of the 
operation. 
The operation. Let us suppose the lower 
bar, K V, of the tumbler to be horizontal, 
and the rod, P O, so situated, as that the 
plugs, or leaden pistons, D and E, shall lie 
opposite to each other, and stop the water 
ways, G and F. In this state of the engine, 
though each of these pistons is pressed by a 
force equivalent to more than a thousand 
pounds, they will remain motionless, be- 
cause these actions being contrary to each 
other, they are constantly in equilibrio. The 
great piston, H, being at the bottom of its 
cylinder, the tumbler is to be thrown by 
hand into the position here delineated. Its 
action upon, O P, and consequently upon 
the wheel, Q, draws up tire plug E, and de- 
presses D, so that the water way, F, becomes 
open from A B, and that of G to the pipe 
R : the water consequently descends from 
A to C, thence to F, until it acts above the 
piston F. This pressure forces down the 
piston, and if there be any water below the 
piston, it causes it to pass through G G G 
into R : during the fall of the piston, which 
carries the pit rod, M N, along with it, a 
sliding block of wood, I, (dotted) fixed to 
this rod is brought into contact with the tail, 
K, of the tumbler, and lowers it to the hori- 
zontal position beyond which it oversets by 
the acquired motion of the weight L. 
The mere rising of the piston, if there 
was no additional motion in the tumbler, 
would only bring the two plugs, D and E, to 
the position of rest, namely, to close G and 
F, and then the engine would stop ; but the 
fall of the tumbler carries the plug, D, up- 
wards, quite clear of the hole, F, and the 
other plug, E, downwards, quite clear of the 
hole, G: these motions require no consump- 
tion of power, because the plugs are in 
equilibrio, as was just observed. In this 
new situation the column, A B, no longer- 
