witty, a is the cylinder, which is supplied 
tVith steam from the boiler through the pipe 
b ; c is the piston in the act of going up ; d is 
the pipe that conducts the steam into the 
condenser e, which consists of two cylinders, 
one within the other, leaving a small space 
between them, into which the steam is ad- 
mitted; while the inner cylinder is filled 
with cold water, and also the external cy- 
linder surrounded by the same ; so that, by 
this means, a very large surface of steam is 
exposed, though no water is suffered to 
come into actual contact with it. 
To the bottom of the piston, c, is attached 
a rod, with another piston, e, working in the 
pipe d. When the piston e arrives at the 
bottom of the cylinder, a valve which is in 
the piston, is opened by its pressing against 
the bottom, and opens a communication 
with the condenser, whilst the spring k, fixed 
to the rod of the piston, shuts the valve 
which admits the steam from the boiler, 
'ilie steam, therefore, being thus condensed, 
runs into the lower pipe f. The piston e, 
arriving at the bottom of the pipe in which 
it works at the same time with c, presses 
upon the condensed water, shuts the valve f, 
and forces the w r ater up the pipe g, into the 
box h. The air which is disengaged from 
the water, rises to the top of the box, and, by 
its elasticity, forces the water through the 
pipe i, which carries it back again into the 
boiler. When the air accumulates in the 
box to such a degree as to depress the water, 
the ball-cock falls with it, and opens a valve 
in the top of the box, which suffers some of 
the air to escape. 
When all the steam is condensed, the mo- 
tion of the fly attached to the machine 
brings the piston up again, its valve now re- 
maining shut by its weight. On arriving at 
the top, it presses up the steam-valve, which 
admits the steam from the boiler to force it 
down as before. 
1 and m are two cranks, upon whose axis 
are two equal wheels working in each other, 
for the purpose of converting the perpen- 
dicular motion of the piston-rod into a ro- 
tatory motion, for working the machinery 
attached to it. 
But the most valuable part of this engine 
is in the construction of the piston, which 
Mr. Cartwright made wholly of metal, and 
so as, by means of springs, to fit the cylinder 
very exactly 7 . This not only saves the ex- 
pence and trouble of packing, which they are 
obliged frequently to renew in all other en- 
gines, but also saves a great deal of steam, 
on account of the more accurate fitting of 
the piston. 
As it is evident, from its construction, that 
the whole of the steam is brought back again 
into the boiler, it affords the means of em- 
ploying ardent spirit instead of water, and 
thus saving a great deal of fuel. 
This machine seems to be peculiarly ap- 
plicable to purposes requiring only a small 
power, as it is not expensive, and occupies 
little room. 
It would for exceed the limits of this work, 
to enter into an examination of all the steam- 
engines invented by different persons. It is 
sufficient to mention, that no engine of this 
kind has been found, upon careful trial, to 
be superior to thoSe of Mr. Watt. 
engines. 
From this brief description of the steam- 
engine, the readier will be enabled to per- 
ceive the nature, and appreciate the value, 
of Mr. Watt’s improvements. It had hitherto 
been the practice to condense the steam in 
the cylinder itself, by the injection of cold 
water ; but the water which is injected ac- 
quires a considerable degree of heat from 
the cylinder, and being placed in air highly 
rarefied, part of it is converted into steam, 
which resists the piston, and diminishes the 
power of the engine. When the steam is 
next admitted, part of it is converted into 
water by coming in contact with the cy- 
linder, which is of a lower temperature than 
the steam, in consequence of the destruction 
of its heat by the injection- water. By con- 
densing the steam, therefore, in the cylinder 
itself, the resistance to the piston is increased 
by a partial reproduction of this elastic va- 
pour, and the impelling power is diminished 
by a partial destruction of the steam which 
is next admitted. Both these inconveni- 
ences Mr. Watt has in a great measure 
avoided, by using a condenser separate from 
the cylinder, and encircled with cold water ; 
and by surrounding the cylihder with a 
wooden case, and interposing light wood- 
ashes, in order to prevent its heat from 
being abstracted by the ambient air. 
The greatest of Mr. Watt’s improvements 
consists in his employing the steam both to 
elevate and depress the piston. In the en- 
gines of Newcomen and Beighton, the steam 
was not the impelling power it: was used 
merely for producing a vacuum below the 
piston, which was forced down by the pres- 
sure of the atmosphere, and elevated by the 
counterweight at the farther extremity of 
the great beam. The cylinder, therefore, 
was exposed to the external air at every de- 
scent of the piston, and a considerable por- 
tion of its heat being thus abstracted, a cor- 
responding quantity of steam was of conse- 
quence destroyed. In Mr. Watt’s engines, 
however, the external air is excluded by a 
metal plate at the top of the cylinder, which 
has a hole in it for admitting the piston-rod; 
and the piston itself is raised and depressed 
merely by the force of steam. 
When these improvements are adopted, 
and the engine is constructed in the most 
perfect manner, there is not above * part of 
the steam consumed in heating the appa- 
ratus ; and, therefore, it is impossible that 
the engine can be rendered £ more powerful 
than it is at present. It would be very de- 
sirable, however, that the force of the piston 
could be properly communicated to the ma- 
chinery without the intervention of the great 
beam. This, indeed, has been attempted by 
Mr. Watt, who has employed the piston-rod 
itself to drive the machinery; and Mr. 
Cartwright has, in his engine, converted tire 
perpendicular motion of the piston into a 
rotatory motion, by means of two cranks 
fixed to the axis of two equal wheels which 
work in each other. Notwithstanding the 
simplicity of these methods, none of them 
have come into general use; and Mr. Watt 
still prefers the intervention of the great 
beam, which is generally made of hard oak, 
with its heart taken out, in order to prevent 
it from warping. A considerable quantity 
of power, however, is wasted by dragging, at 
4 1(2 
52/ 
every stroke of the piston, such a mass of 
matter from a state of rest to a state of 
motion, and then from a state of motion to a 
state of rest. To prevent this loss of power, a 
light frame of carpentry has been employed by 
several engineers, instead of the solid beam ; 
but alter being used for some time, the wood 
was generally cut by the iron bolts, and the 
frame itself was often instantaneously de- 
stroyed. In some of the engines lately con- 
structed by Mr. Watt, he lias formed the 
great beam of cast iron, and while he has 
thus added to its durability, he has at the 
same time diminished its weight and in- 
creased the power of his engine. 
Encouraged by Mr. Watt’s success, se- 
veral improvements upon the steam-en- 
gine have been attempted by Hornblower, 
Trevethick, and many other engineers of 
this country. But it does not appear that 
they have either increased the power of the 
engine, or diminished its expence. It ap- 
pears, on the contrary, that many of these 
pretended improvements, excepting those of 
Hornblower, consist merely in having adopt- 
ed Mr. Watt’s discoveries, in such a manner 
as not to infringe upon his patent. 
Some time since, [Mr. Arthur Woolf an- 
nounced to the public a discovery respect- 
ing the expansibility of steam, which pro- 
mises to be of very essential utility. Mr. 
Watt had formerly ascertained, that steam 
which acts witli the expansive force of four 
pounds per square inch, against a safety 
valve exposed to the weight of the atmo- 
sphere, after expanding itself to four times 
the vo!ulne it thus occupies, is still equal to 
the pressure of the atmosphere. But Mr. 
Woolf has gone much farther, and has proved, 
that quantities of steam, having the force 
of 5, 6, 7, 8, 9, 10, &c. pounds on every 
square inch, may be allowed to expand 5, 6, 
7, 8, 9, 10, &c. times its volume, and will 
still be equal to the atmosphere’s weight, 
provided that the cylinder in which the ex- 
pansion takes place, has the same tempe- 
rature as the steam before it began to expand. 
It is evident, however, that an increase of 
temperature is necessary both to produce and 
to maintain this augmentation of the steam’s 
expansive force above the pressure of the 
atmosphere. At the temperature of 212° of 
Fahrenheit, the force of steam is equal only 
to the pressure of the atmosphere: and in 
order to give it an additional elastic force of 
five pounds per square inch, the temperature 
must be increased to about 227” ; when it 
will have acquired a power to expand itself 
to five times its volume, and still be equal in 
pressure to the atmosphere, and capable of 
being applied as such in the working of steam- 
engines, according to his invention. The 
ratio of other pressures, temperatures, and 
expansive forces of steam, is shewn in the 
following table ; which gives the relative pres- 
sure per square inch, temperatures, and ex- 
pansibility of steam, at degrees of heat above 
the boiling point of water; beginning with a 
temperature of steam of an elastic force 
equal to five pounds per square inch, and 
extending to steam able to sustain forty 
pounds on the square inch. 
