216 
MAGAZINE OF SCIENCE AND ART. 
cast brass, and is accurately fitted by grinding, 
so as to be steam tight. 
The steam-pipe is directly connected with the 
steam-tube, and is 11} inches in diameter, and 
where it joins the nozzle of the governor valve 
it has a rectangular opening of 1 foot 4 inches 
by 5 inches. The whole of this pipe is enclosed 
in a case, or bos, filled with saw-dust to prevent 
radiation. 
The cduction-pipe, leading from the bottom 
nozzle to the condenser, lias an internal diameter 
of 1 foot 4 inches. This pipe may be said to 
perform a part of the duty of the condenser, as 
from its great length, the steam is in a great 
measuro condensed within it before it reaches 
the condenser. 
The condenser is 1 foot 3 inches in diameter 
by 5 feet 4 inches in height; this height is, how¬ 
ever, increased by a cap piece 1 foot 10 inches in 
height. 
The air-pump has an internal diameter of 2 
feet 10 inches. The cistern for containing the 
hot water drawn off from the condenser is placed 
immediately above it. and is 4 feet 4 inches in 
diameter by 2 feet 2 inches in depth. 
The engine is worked by means of the four 
following valves, viz.;— 
1. The governor valve. 
2. The steam-expansion valve. 
3. The equilibrium valve. 
4. The exhaust valve. 
These three last valves are nearly of the same 
form, although of different dimensions; they are 
what is termed “ double-lieat valves,” and pos¬ 
sess the advantages of effecting a large opening, 
and requiring little force to work them. 
The exhaust-valve is the largest of the three- 
being 20 inches in diameter, while the steam, 
expansion valve has an opening of only 10 
inches, and from their arrangement they may bo 
worked either by the plug-rod of the engine or 
manipulated. Their action is regulated by a 
simple and ingenious contrivance called the 
cataract,” by nieans of which the engineer can 
increase or diminish the number of strokes made 
by the engine. 
. preparing to work the engine all four valves 
are opened, in order to expel or blow through 
the air contained in the cylinder or eduction- 
pipe. The steam expansion valve is then closed, 
and the steam which previously filled the cylin¬ 
der being quickly condensed the steam is let on 
te the top of the piston, which then begins to 
descend. After having passed through from one- 
fifth to one-sixth portion of the stroke the plug- 
rod closes the expansion valve, and the re¬ 
mainder of the stroke is completed under a de¬ 
creasing pressure of the expanding steam until 
the piston is brought, gradually to a state of rest; 
a little before this the exhaust-valve is closed 
and the equilibrium-valve is opened. The steam 
that remains now presses equally both on the 
the top and on the bottom of the piston, which 
being thus “ in equilibrio” would remain pas¬ 
sively in its plafe at the bottom of the cylinder, 
but that tho i>reponderating weight of the plun¬ 
ger-poles, pump-rods and counterpoise at the 
other end of the balance-beam at this moment 
comes into play and raises the piston to the top 
of the cylinder, at the same time that the water 
is delivered by the pumps through the ascending 
main pipe placed in the well. A little before the 
end of the stroke tho plug-rod closes tho equili¬ 
brium-valve, and the piston is brought gradually 
to a state of rest by the resistance of a small 
quantity of steam imprisoned between the top of 
the piston and the cylinder cover, which acts as 
an elastic “ cushion” to provent the piston from 
rising too high and striking the iatter. Thus, a 
complete stroke of the engine has been performed 
and the piston remains at rest until by the 
action of the cataract the exhaust-valve and the 
expansion-value are successively opened, and the 
engine commences a second stroke. Thus the 
successive strokes of the engine are always sepa¬ 
rated by a short interval, the duration of which 
can he regulated. The opening of the exhaust- 
valve a few seconds before tho expansion-valve 
is requisite, inasmuch as the vacuum is com¬ 
pleted at the instant, of the opening of the latter. 
The engine now becomes automatic, hut the 
attention of the engineer is constantly required 
to be directed to the governor-valve, as it has 
sometimes happened that from this valve being 
opened too wide, and the steam in the boilers 
being at the same time too high, the pressure on 
the piston has been so great that the latter has 
travelled too far, and has broken the cylinder 
bottom. 
In order, ns far as possible, to prevent such an 
occurrence, the balance beam is furnished with an 
appendage fixed near its extremity, close to the 
top of the piston rod, composed of two east-iron 
standards supporting a horizontal catch piece 
also of iron ; which when the piston is at its 
lowest point, rests upon two pieces of wood, fixed 
upon the spring beams. Theso pieces act as 
springs to break the forco of tho blow should the 
piston descend too far, and endanger the bottom 
of the cylinder. Sometimes this catch is made 
to touch the handle of a hell before striking the 
wood springs, and the attendant is thus warned 
that the quantity of steam admitted through the 
governor-value must be diminished. It will be 
seen that while the interval of time elapsing be¬ 
tween two consecutive strokes of tho engine may¬ 
be varied by means of tho cataract, tho engineer 
has also tho means of increasing or diminishing 
the portion of time during which the steam is 
admitted on to the piston through the expan¬ 
sion value. This is done by means of a chock 
or plug which is made to slide along the plug rod, 
and which can bo fixed in any position required 
so as to Bhutthe value at any given portion of the 
stroke. Thus the steam can be shut off at 1-4, 
1-5,1-G, 17, or any less portion of tho stroke, 
anil the adjustment can he made in a few min¬ 
utes, according to the degree of expansion re¬ 
quired. In this way the steam expended will be 
in proportion to the work to be dono. An en¬ 
gine in Cornwall is said to he going “ in doors,” 
or performing the “ in door ” stroke, when the 
steam valve is opened, and the piston is conse¬ 
quently in the act of descending. ThiB is equi¬ 
valent to what is called the working stroke of a 
Boulton and Watt engine. And an engine is said 
to bo going “ out of doors,” or performing the 
“ out door ” when the preponderance of the pump 
rods or counterweights is bringing the piston 
again to the top of tho cylinder. In practice the 
“ in door ” stroke is always performed in a less 
space of time than the “ out door ” or return 
stroke : should, therefore, the weight of the pump 
rods or counterpoise he too great, the velocity of 
