necessary to provide. The cold water admitted through the jet to
condense the steam, mixed with the condensed steam itself, would
gradually collect in the vessel C, and at length choke it. To
prevent this, Watt proposed to put the vessel C in communication
with a pump F, which might be wrought by the engine itself, and by
which the water, which would collect in the bottom of the vessel
C, would be constantly drawn off. This pump would be evidently
rendered the more necessary, since more or less atmospheric air,
always combined with water in its common state, would enter the
vessel C by the condensing jet. This air would be disengaged in
the vessel C by the heat of the steam condensed therein; and it
would rise through the tube S, and vitiate the vacuum in the
cylinder;—an effect which would be rendered the more injurious,
[Pg123] inasmuch as, unlike steam, this elastic fluid would be
incapable of being condensed by cold. The pump F, therefore, by
which Watt proposed to draw off the water from the vessel C, might
also be made to draw off the air, or the principal part of it.
The vessel C was subsequently called a _condenser_; and, from the
circumstances just adverted to, the pump F has been called the
_air-pump_.
These—namely, the cylinder, the condenser, and the air-pump—were
the three principal parts in the invention, as it first presented
itself to the mind of Watt—and even before it was reduced to a
model, or submitted to experiment. But, in addition to these,
other two improvements offered themselves in the very first stage
of its progress.
In the atmospheric engine, the piston was maintained steam-tight
in the cylinder by supplying a stream of cold water above it, by
which the small interstices between the piston and cylinder would
be stopped. It is evident that the effect of this water as the
piston descended would be to cool the cylinder, besides which any
portion of it which might pass between the piston and cylinder and
which would pass below the piston, would boil the moment it would
fall into the cylinder, which itself would be maintained at the
boiling temperature. This water, therefore, would produce steam,
the pressure of which would resist the descent of the piston.
Watt perceived, that even though this inconvenience were removed
by the use of oil or tallow upon the piston, still, that as the
piston would descend in the cylinder, the cold atmosphere would
follow it; and would, to a certain extent, lower the temperature
of the cylinder. On the next ascent of the piston, this
temperature would have to be again raised to 212° by the steam
coming from the boiler, and would entail upon the machine a
proportionate waste of power.
If the atmosphere of the engine-house could be kept heated to the
temperature of boiling water, this inconvenience would be removed.
The piston would then be pressed down by air as hot as the steam
to be subsequently introduced into it. On further consideration,
however, it occurred to Watt that it would be still more
advantageous if the cylinder itself could be [Pg124] worked in an
atmosphere of steam, having only the same pressure as the
atmosphere. Such steam would press the piston down as effectually
as the air would; and it would have the further advantage over
air, that if any portion of it leaked through between the piston
and cylinder, it would be condensed, which could not be the case
with atmospheric air. He therefore determined on surrounding the
cylinder by an external casing, the space between which and the
cylinder he proposed to be filled with steam supplied from the
boiler. The cylinder would thus be enclosed in an atmosphere of
its own, independent of the external air, and the vessel so
enclosing it would only require to be a little larger than the
cylinder, and to have a close cover at the top, the centre of
which might be perforated with a hole to admit the rod of the
piston to pass through, the rod being made smooth, and so fitted
to the perforation that no steam should escape between them. This
method would be attended also with the advantage of keeping the
cylinder and piston always heated, not only inside but outside;
and Watt saw that it would be further advantageous to employ the
pressure of steam to drive the piston in its descent instead of
the atmosphere, as its intensity or force would be much more
manageable; for, by increasing or diminishing the heat of the
steam in which the cylinder was enclosed, its pressure might be
regulated at pleasure, and it might be made to urge the piston
with any force that might be required. The power of the engine
would therefore be completely under control, and independent of
all variations in the pressure of the atmosphere.
(70.) This was a step which totally changed the character of the
machine, and which rendered it a STEAM ENGINE instead of an
ATMOSPHERIC ENGINE. Not only was the vacuum below the piston now
produced by the property of steam, in virtue of which it is
reconverted into water by cold; but the pressure which urged the
piston into this vacuum was due to the elasticity of steam.
The external cylinder, within which the working cylinder was
enclosed, was called THE JACKET, and is still very generally used.
[Illustration: _Fig._ 20.]
(71.) The first experiment in which Watt attempted to [Pg125]
realise, on a small scale, his conceptions, was made in the
following manner. The cylinder of the engine was represented by a
brass syringe A B (_fig._ 20.) an inch and a third in diameter, and
ten inches in length, to which a top and a bottom of tin plate was
fitted. Steam was conveyed by a pipe, S, from a small boiler into
the lower end of this syringe, a communication being made with the
upper end of the syringe by a branch pipe D. For the greater
convenience of the experiment, it was found desirable to invert the
position of the cylinder, so that the steam should press the piston
P upwards instead of downwards. The piston-rod R therefore was
presented downwards. An eduction pipe E was also inserted in the top
of the cylinder, which was carried to the condenser. The piston-rod
was made hollow, or rather a hole was drilled longitudinally through
it, and a valve was fitted at its lower end, to carry off the water
produced by the steam, which [Pg126] would be condensed in the
cylinder in the commencement of the process. The condenser used in
this experiment operated without injection, the steam being
condensed by the contact of cold surfaces. It consisted of two thin
pipes F, G of tin, ten or twelve inches in length, and the sixth of
an inch in diameter, standing beside each other perpendicularly, and
communicating at the top with the eduction pipe, which was provided
with a valve opening upwards. At the bottom these two pipes
communicated with another tube I of about an inch in diameter, by a
horizontal pipe, having in it a valve, M, opening towards I, fitted
with a piston K, which served the office of the air-pump, being
worked by the hand. This piston, K, had valves in it opening
upwards. These condensing pipes and air-pump were immersed in a
small cistern, filled with cold water. The steam was conveyed by the
steam-pipe S to the bottom of the cylinder, a communication between
the top and bottom of the cylinder being occasionally opened by a
cock, C, placed in the branch pipe. The eduction pipe leading to the
condenser also had a cock, L, by which the communication between the
top of the cylinder and the condenser might be opened and closed at
pleasure. In the commencement of the operation, the cock N admitting
steam from the boiler, and the cock L opening a communication
between the cylinder and the condenser, and the cock C opening a
communication between the top and bottom of the cylinder, being all
open, steam rushed from the boiler, passing through all the pipes,
and filling the cylinder. A current of mixed air and steam was thus
produced through the eduction pipe E, through the condensing pipes F
and G, and through the air-pump I, which issued from the valve H in
the eduction pipe, and from the valve in the air-pump piston, all of
which opened upwards. The steam also in the cylinder passed through
the hole drilled in the piston-rod, and escaped, mixed with air,
through the valve in the lower end of that rod. This process was
continued until all the air in the cylinder, pipes, and condenser,
was blown out, and all these spaces filled with pure steam. The
cocks L, C, and N, were then closed, and the atmospheric pressure
closed the valve H and the valves in the air-pump piston. The cold
surfaces condensing the steam in [Pg127] the pipes F and G, and in
the lower part of the air-pump, a vacuum was produced in these
spaces. The cock C being now closed, and the cocks L and N being
open, the steam in the upper part of the cylinder rushed through the
pipe E into the condenser, where it was reduced to water, so that a
vacuum was left in the upper part of the cylinder. The steam from
the boiler passing below the piston, pressed it upwards with such
force, that it lifted a weight of eighteen pounds hung from the end
of the piston-rod. When the piston reached the top of the cylinder,
the cocks L and N were closed, and the cock C opened. All
communication between the cylinder and the boiler, as well as
between the cylinder and the condenser, were now cut off, and the
steam in the cylinder circulated freely above and below the piston,
by means of the open tube D. The piston, being subject to equal
forces upwards and downwards, would therefore descend by its own
weight, and would reach the bottom of the cylinder. The air-pump
piston meanwhile being drawn up, the air and the condensed steam in
the tubes F and G were drawn into the air-pump I, through the open
horizontal tube at the bottom. Its return was stopped by the valve
M. By another stroke of the air-pump, this water and air were drawn
out through valves in the piston, which opened upwards. The cock C
was now closed, and the cocks L and N opened, preparatory to another
stroke of the piston. The steam in the upper part of the cylinder
rushed, as before, into the tubes F and G, and was condensed by
their cold surfaces, while steam from the boiler coming through the
pipe S, pressed the piston upwards. The piston again ascended with
the same force as before, and in the same manner the process was
continually repeated.
(72.) The quantity of steam expended in this experimental model in
the production of a given number of strokes of the piston was
inferred from the quantity of water evaporated in the boiler; and
on comparing this with the magnitude of the cylinder and the
weight raised by the pressure of the steam, the contrivance was
proved to affect the economy of steam, as far as the imperfect
conditions of such a model could have permitted. A larger model
was next constructed, having an outer cylinder, or steam case,
surrounding the working cylinder, and [Pg128] the experiments
made with it fully realised Watt's expectations, and left no doubt
of the great advantages which would attend his invention. The
weights raised by the piston proved that the vacuum in the
cylinder produced by the condensation was almost perfect; and he
found that when he used water in the boiler which by long boiling
had been well cleared of air, the weight raised was not much less
than the whole amount of the pressure of the steam upon the
piston. In this larger model, the cylinder was placed in the usual
position, with a working lever and other apparatus similar to that
employed in the Atmospheric Engine.
(73.) It was in the beginning of the year 1765, Watt being then in
the twenty-ninth year of his age, that he arrived at these great
discoveries. The experimental models just described, by which his
invention was first reduced to a rude practical test, were fitted
up at a place called Delft House, in Glasgow. It will doubtless,
at the first view, be a matter of surprise that improvements of
such obvious importance in the economy of steam power, and capable
of being verified by tests so simple, were not immediately adopted
wherever atmospheric engines were used. At the time, however,
referred to, Watt was an obscure artisan, in a provincial town,
not then arrived at the celebrity to which it has since attained,
and the facilities by which inventions and improvements became
public were much less than they have since become. It should also
be considered that all great and sudden advances in the useful
arts are necessarily opposed by the existing interests with which
their effects are in conflict. From these causes of opposition,
accompanied with the usual influence of prejudice and envy, Watt
was not exempt, and was not therefore likely suddenly to
revolutionise the arts and manufactures of the country by
displacing the moving powers employed in them, and substituting an
engine, the efficacy and power of which depended mainly on
physical principles, then altogether new and but imperfectly
understood.
Not having the command of capital, and finding it impracticable to
inspire those who had, with the same confidence in the advantages
of his invention which he himself felt, he was [Pg129] unable to
take any step towards the construction of engines on a large
scale. Soon after this, he gave up his shop in Glasgow, and
devoted himself to the business of a Civil Engineer. In this
capacity he was engaged to make a survey of the river Clyde, and
furnished an elaborate and valuable Report upon its projected
improvements. He was also engaged in making a plan of the canal,
by which the produce of the Monkland Colliery was intended to be
carried to Glasgow, and in superintending the execution of that
work. Besides these, several other engineering enterprises
occupied his attention, among which may be mentioned, the
navigable canal across the isthmus of Crinan, afterwards completed
by Rennie; improvements proposed in the ports of Ayr, Glasgow, and
Greenock; the construction of the bridges at Hamilton, and at
Rutherglen; and the survey of the country through which the
celebrated Caledonian canal was intended to be carried.
"If, forgetful of my duties as the organ of this academy," says M.
Arago (whose eloquent observations on the delays of this great
invention, addressed to the assembled members of the National
Institute of France, we cannot forbear to quote), "I could think
of making you smile, rather than expressing useful truths, I would
find here matter for a ludicrous contrast. I would call to your
recollection the authors, who at our weekly sittings demand with
all their might and main (_à cor et à cris_) an opportunity to
communicate some little remark—some small reflection—some
trifling note, conceived and written the night before; I would
represent them to you cursing their fate, when according to your
rules, the reading of their communication is postponed to the next
meeting, although during this cruel week, they are assured that
their important communication is deposited in our archives in a
sealed packet. On the other hand, I would point out to you the
creator of a machine, destined to form an epoch in the annals of
the world, undergoing patiently and without murmur, the stupid
contempt of capitalists,—conscious of his exalted genius, yet
stooping for eight years to the common labour of laying down
plans, taking levels, and all the tedious calculations connected
with the routine of common engineering. While in this conduct you
cannot fail to recognise the serenity, [Pg130] the moderation,
and the true modesty of his character, yet such indifference,
however noble may have been its causes, has something in it not
altogether blameless. It is not without reason that society visits
with severe reprobation those who withdraw gold from circulation
and hoard it in their coffers. Is he less culpable who deprives
his country, his fellow citizens, his age, of treasures a thousand
times more precious than the produce of the mine; who keeps to
himself his immortal inventions, sources of the most noble and
purest enjoyment of the mind, who abstains from conferring upon
labour those powers, by which would be multiplied in an infinite
proportion the products of industry, and by which, with advantage
to civilisation and human nature, he would smooth away the
inequalities of the conditions of man."[19]
(74.) Although Watt was thus attracted by pursuits foreign to his
recent investigations respecting the improvement of steam power,
he never lost sight of that object. It was not until the year
1768, three years after his great discoveries, that any step was
taken to enable him to carry them into effect on a large scale. At
that time his friends brought him into communication with Dr.
Roebuck, the proprietor of the Carron Iron Works, who rented
extensive coal works at Kinneal from the Duchess of Hamilton. Watt
was first employed by Roebuck as a civil engineer; but when he
made known to him the improvements he had projected in the steam
engine, Roebuck proposed to take out a patent for an engine on the
principle of the model which had been fitted up at Delft House,
and to join Watt in a partnership, for the construction of such
engines. Sensible of the advantages to be derived from the
influence of Roebuck, and from his command of capital, Watt agreed
to cede to him two thirds of the advantages to be derived from the
invention. A patent was accordingly taken out on the fifth of
January, 1769, nearly four years after the invention had been
completed; and an experimental engine on a large scale was
constructed by him, and fitted up at Kinneal House. In the first
trial this machine more than fulfilled Watt's anticipations. Its
[Pg131] success was complete. In the practical details of its
construction, however, some difficulties were still encountered,
the greatest of which consisted in packing the piston, so as to be
steam-tight. The principle of the new engine did not admit of
water being kept upon the piston, to prevent leakage, as in the
old engines; he was therefore obliged to have his cylinders much
more accurately bored, and more truly cylindrical, and to try a
great variety of soft substances for packing the piston, which
would make it steam-tight without great friction, and maintain it
so in a situation perfectly dry, and at the temperature of boiling
water.
While Watt was endeavouring to overcome these and other
difficulties, in the construction of the machine, his partner, Dr.
Roebuck, became embarrassed, by the failure of his undertaking in
the Borrowstowness coal and salt works; and he was unable to
supply the means of prosecuting with the necessary vigour the
projected manufacture of the new engines.
The important results of Watt's labours having happily at this
time become more publicly known, Mr. Matthew Boulton, whose
establishment at Soho, near Birmingham, was at that time the most
complete manufactory for metal-work in England, and conducted with
unexampled enterprise and spirit, proposed to purchase Dr.
Roebuck's interest in the patent. This arrangement was effected in
the year 1773, and in the following year Mr. Watt removed to Soho,
where a portion of the establishment was allotted to him, for the
erection of a foundery, and other works necessary to realise his
inventions on a grand scale.
The patent which had been granted in 1769 was limited to a period
of fourteen years, and would consequently expire about the year
1783. From the small progress which had hitherto been made in the
construction of engines upon the new principle, and from the many
difficulties still to be encountered, and the large expenditure of
capital which must obviously be incurred before any return could
be obtained, it was apparent that unless an extension of the
patent right could be obtained, Boulton and Watt could never
expect any advantage adequate to the risk of their great [Pg132]
enterprise. In the year 1774 an application was accordingly made
to parliament for an extension of the patent, which was supported
by the testimony of Dr. Roebuck, Mr. Boulton, and others, as to
the merits and probable utility of the invention. An Act was
accordingly passed, in 1775, extending the term of the patent
until the year 1800.
(75.) The following abstract of this Act may not be uninteresting
at this time, when the anticipations expressed in it have been so
successfully and extensively realised:—
"An Act for vesting in James Watt, engineer, his executors,
administrators, and assigns, the sole use and property of certain
steam engines, commonly called fire engines, of his invention,
throughout his majesty's dominions, for a limited time:
"And whereas the said James Watt hath employed many years, and a
considerable part of his fortune, in making experiments upon steam
engines, commonly called fire engines, with a view to improve
those very useful machines, by which several very considerable
advantages over the common steam engines are acquired; but upon
account of the many difficulties which always arise in the
execution of such large and complex machines, and of the long time
requisite to make the necessary trials, he could not complete his
intention before the end of the year 1774, when he finished some
large engines as specimens of his construction, which have
succeeded, so as to demonstrate the utility of the said invention:
"And whereas, in order to manufacture these engines with the
necessary accuracy, and so that they may be sold at moderate
prices, a considerable sum of money must be previously expended in
erecting mills and other apparatus; and as several years and
repeated proofs will be required before any considerable part of
the public can be fully convinced of the utility of the invention,
and of their interest to adopt the same, the whole term granted by
the said letters patent may probably elapse before the said James
Watt can receive an advantage adequate to his labour and
invention:
"And whereas, by furnishing mechanical power at much less expense,
and in more convenient forms, than has hitherto been done, his
engines may be of great utility, in facilitating [Pg133] the
operations in many great works and manufactures of this kingdom;
yet it will not be in the power of the said James Watt to carry
his invention into that complete execution which he wishes, and so
as to render the same of the highest utility to the public of
which it is capable, unless the term granted by the said letters
patent be prolonged, and his property in the said invention
secured for such time as may enable him to obtain an adequate
recompense for his labour, time, and expense:
"To the end, therefore, that the said James Watt may be enabled
and encouraged to prosecute and complete his said invention, so
that the public may reap all the advantages to be derived
therefrom in their fullest extent: it is enacted,
"That from and after the passing of this Act, the sole privilege
and advantage of making, constructing, and selling the said
engines hereinbefore particularly described, within the kingdom of
Great Britain, and his majesty's colonies and plantations abroad,
shall be, and are hereby declared to be, vested in the said James
Watt, his executors, administrators, and assigns, for and during
the term of twenty-five years," &c. &c.
(76.) Thus protected and supported, Watt now directed the whole
vigour of his mind to perfect the practical details of his
invention, and the result was, the construction on a large scale
of the engine which has since been called his SINGLE ACTING STEAM
ENGINE.
It is necessary to recollect, that notwithstanding the extensive and
various application of steam power in the arts and manufactures, at
the time to which our narrative has now reached, the steam engine
had never been employed for any other purpose save that of raising
water by working pumps. The motion, therefore, which was required
was merely an upward force, such as was necessary to elevate the
piston of a pump, loaded with the column of water which it raised.
The following then is a description of the improved engine of Watt,
by which such work was proposed to be performed:—
[Illustration: _Fig._ 21.]