THE STEAM ENGINE
The greatest of the world’s inventions appear to have had a very casual
birth. So much an affair of chance has been their first manifestation,
that science has not been called in aid; no law can be discerned which
might govern the time and sequence of their coming; they seem to have
been stumbled on, unpedigreed offspring of accident and time. A monk of
Metz discovers gunpowder. “Surely,” says Fuller, “ingenuity may seem
transposed, and to have crossed her hands, when about the same time
a soldier found out printing.” “It should seem,” writes Lord Bacon,
“that hitherto men are rather beholden to a wild goat for surgery, or
to a nightingale for music, or to the ibis for some part of physic, or
to the pot-lid that flew open for artillery, or generally to chance,
or anything else, than to logic for the invention of the Arts and
Sciences.” So it seemed. And in due time the legend of the pot-lid
was woven round the unfortunate Marquis of Worcester, who, tradition
had it, made the discovery of the steam engine by observation of the
stew-pot in which, when confined a prisoner in the Tower, he was
engaged in cooking his dinner. At a later date and in another form the
story was connected with James Watt.
In reality, the story of the discovery of the steam engine is far more
inspiring. The history of the application of steam to human use is
almost the history of science itself; the stages of its development are
clearly marked for us; and the large succession of these stages, and
the calibre of the minds which contributed to the achievement of the
perfected steam engine, are some measure of the essential complexity
of what is to-day regarded as a comparatively simple machine. For the
steam engine was not the gift of any particular genius or generation;
it did not leap from any one man’s brain. Some of the greatest names
in the history of human knowledge can claim a share in its discovery.
From philosopher to scientist, from scientist to engineer the grand
idea was carried on, gradually taking more and more concrete form,
until finally, in an age when by the diffusion of knowledge the labours
of all three were for the first time co-ordinated, it was brought
to maturity. A new force of nature was harnessed which wrought a
revolution in the civilized world.
An attempt is made in this chapter to chronicle the circumstances under
which the successive developments of the steam engine took place. The
progress of the scientific ideas which led up to the discovery of the
power of steam is traced. The claims of the various inventors chiefly
associated with the steam engine are set forth in some detail, not for
the difficult and invidious task of assessing their relative merits,
but because by the light of these claims and altercations it may be
possible to discern, in each case, where the merit lay and to what
stage each novelty of idea or detail properly belonged. From this point
of view, it is thought, the recital of circumstances which hitherto
have been thought so trivial as to be scarcely worthy of record, may be
of some suggestive value. The result of the investigation is to make
clear the scientific importance of the steam engine: the steam engine
regarded, not as the familiar drudge and commonplace servant of to-day,
but in all its dignity of a thermodynamic machine, that scientific
device which embodied so much of the natural philosophy of the age
which first unveiled it--the seventeenth century.
§
Before the Christian era steam had been used to do mechanical work.
In a treatise, _Pneumatica_, written by Hero of Alexandria about 130
B.C., mention is made of a primitive reaction turbine, which functioned
by the reactionary force of steam jets thrown off tangentially from
the periphery of a wheel. In the same work another form of heat-engine
is described: an apparatus in which, by the expansion from heating of
air contained in a spherical vessel, water was expelled from the same
vessel to a bucket, where by its weight it gave motion mysteriously
to the doors of temples. And evidence exists that in these two forms
heat engines were used in later centuries for such trivial purposes as
the blowing of organs and the turning of spits. But except in these
two primitive forms no progress is recorded for seventeen centuries
after the date of Hero’s book. The story of the evolution of steam as a
motive force really begins, with the story of modern science itself, at
the end of the Middle Ages.
With the great revival of learning which took place in Southern Europe
in the latter part of the fifteenth century new light came to be thrown
on the classical philosophies which still ruled men’s minds, and modern
science was born. New views on natural phenomena began to irradiate,
and, sweeping aside the myths and traditions which surrounded and
stifled them, the votaries of the “new science” began to formulate
opinions of the boldest and most unorthodox description.[70] The true
laws of the equilibrium of fluids, discovered originally by Archimedes,
were rediscovered by Stevinus. By the end of the sixteenth century the
nature of the physical universe was become a pursuit of the wisest men.
To Galileo himself was due, perhaps, the first distinct conception of
the power of steam or any other gas to do mechanical work; for “he,
the Archimedes of his age, first clearly grasped the idea of force as
a mechanical agent, and extended to the external world the conception
of the invariability of the relation between cause and effect.”[71]
To his brilliant pupil Torricelli the questioning world was indebted
for the experiments which showed the true nature of the atmosphere,
and for the theory he proclaimed that the atmosphere by its own weight
exerted its fluid pressure--a theory which Pascal soon confirmed by the
famous ascent of his barometer up the Puy-de-Dôme, which demonstrated
that the pressure supporting his column of mercury grew less as the
ascent proceeded. Giovanni della Porta, in a treatise on pneumatics
published in the year 1601, had already made two suggestions of the
first importance. Discussing Hero’s door-opening apparatus, della
Porta showed that steam might be substituted for air as the expanding
medium, and that, by condensing steam in a closed vessel, water might
be sucked up from a lower level by virtue of the vacuum so formed. And
a few years later, in 1615, Solomon de Caus, a French engineer, had
come to England with a scheme almost identical with della Porta’s, and
actually constructed a plant which forced up water to a height by means
of steam. Shortly afterwards the “new science” received an accession of
interest from the invention, by Otto von Guericke of Magdeburg, of a
suction pump by which the atmospheric air could be abstracted from a
closed vessel.
By the middle of this century the learned of all European countries had
been attracted by the knowledge gained of the material universe. In
England the secrets of science were attacked with enthusiasm under the
new strategy of Lord Bacon, enunciated in his _Novum Organum_. The new
philosophy was patronised by royalty itself, and studied by a company
of brilliant men of whom the leading physicist was Robert Boyle, soon
famous for his law connecting the volumes and the pressures of gases.
In France, too, a great enthusiasm for science took birth. A group of
men, of whom the most eminent was Christian Huyghens, banded themselves
together to further scientific inquiry into the phenomena of nature
and to demolish the reigning myths and fallacies: they also working
admittedly by the experimental method of Bacon.
The time was ripe, however, for wider recognition of these scientists
and the grand object of their labours. Within a short time the two
groups were both given the charter of their respective countries;
in France they were enrolled as the Royal Academy of Sciences; in
England, as the Royal Society for Improving Natural Knowledge. In
other countries societies of a similar kind were formed, but their
influence was not comparable with that exerted by the societies of
London and Paris. Between these two a correspondence was started which
afterwards developed into one of the most famous of publications:
the _Philosophical Transactions_. In England, especially, the Royal
Society served from its inception as a focus for all the great minds
of the day, and in time brought together such men as Newton, Wren,
Hooke, Wallis, Boyle--not to mention his majesty King Charles himself;
who, with the best intentions, could not always take seriously the
speculations of the savants. “Gresham College he mightily laughed at,”
noted Mr. Pepys in his diary for the first of February, 1663, “for
spending time only in weighing of ayre, and doing nothing else since
they sat.” A year later Pepys was himself admitted a member of the
distinguished company, and found it “a most acceptable thing to hear
their discourse, and see their experiments, which were this day on
fire, and how it goes out in a place where the air is not free, and
sooner out in a place where the ayre is exhausted, which they showed by
an engine on purpose.”
§
In the year 1663, just after the formation of the Royal Society, a
small book was published by the Marquis of Worcester, _A Century of the
Names and Scantlings of such Inventions as he had tried and perfected_.
Of these inventions one, the sixty-eighth, is thus described:
“An admirable and most forcible way to drive up water by fire, not by
drawing or sucking it upwards, for that must be as the Philosopher
calleth it, _Intra sphæram activitatis_, which is but at such a
distance. But this way hath no bounder, if the vessels be strong
enough; for I have taken a piece of a whole cannon, whereof the end
was burst, and filled it three-quarters full of water, stopping and
screwing up the broken end, as also the touch-hole; and making a
constant fire under it, within twenty-four hours it burst and made a
great crack. So that having a way to make my vessels, so that they are
strengthened by the force within them, and the one to fill after the
other; I have seen the water run like a constant fountain-stream forty
foot high; one vessel of water rarified by fire driveth up forty of
cold water. And a man that tends the work is but to turn two cocks,
that one vessel of water being consumed, another begins to force and
refill with cold water, and so successfully, the fire being tended
and kept constant, which the selfsame person may likewise abundantly
perform in the interim between the necessity of turning the said cocks.”
On this evidence the claim is made that the marquis was the original
inventor of the steam engine. Is he at all entitled to the honour? The
whole affair is still surrounded with mystery. It is known that he was
an enthusiastic student of physical science, and that for years he had
working for him a Dutch mechanic, Caspar Kaltoff; it seems certain
that he actually made a water-pumping engine worked by steam, of whose
value he was so impressed that he promised to leave the drawings of
it to Gresham College and intended to have a model of it buried with
him.[72] But neither model nor drawings has ever yet been traced. And,
considering the social influence of the inventor and the importance
of the invention, the silence of his contemporaries on the discovery
is strange and inexplicable. He received a patent for some form of
water-pumping engine. Distinguished visitors came to Vauxhall to see
his engine at work. He numbered among his acquaintances Sir Jonas
Moore, Sir Samuel Morland, Flamstead and Evelyn: probably Mr. Pepys,
Sir W. Petty, and others of the group of eminent men of his time who
were interested in natural science. Yet no trace of his inventions has
come down to us. His _Century_ was admittedly compiled from memory--“my
former notes being lost”--and perhaps it was designedly obscure;
science was at that time a hobby of the cultured few, and scientific
men loved to mystify each other by the exhibition, without explanation,
of paradoxes and toys of their own construction. The marquis, it will
be agreed, left valuable hints to later investigators. Whether his
claim to have invented the steam engine is sufficiently substantiated,
we leave to the opinion of the interested reader, who will find most
of the evidence on this subject in Dirck’s _Life of the Marquis of
Worcester_.
The power of steam to drive water from a lower to a higher level had
been shown by Solomon de Caus,[73] who, in his work, _Les Raisons des
Forces Mouvantes_, published in A.D. 1615, had described a hot-water
fountain operated by heating water in a globe. In Van Etten’s
_Récreation Mathematique_ of 1629 was an experiment, described fifty
years later by Nathaniel Nye in his _Art of Gunnery_ as a “merry
conceit,” showing how the force of steam could be used to discharge a
cannon. As the century advanced the ornamental was gradually superseded
by the utilitarian; the usefulness of steam for draining fens, pumping
out mines, was realized; and applications for patents to cover the use
of new and carefully guarded inventions began to appear.
Gunpowder as a medium was a strong competitor of steam. In 1661 King
Charles granted to Sir Samuel Morland, his master of mechanics, “for
the space of fourteen years, to have the sole making and use of a new
invention of a certain engine lately found out and devised by him, for
the raising of water out of any mines, pits, or other places, to any
reasonable height, and by the force of air and powder conjointly.”
What form the engine took is not known; whether the gunpowder was
used to produce a gaseous pressure by which the work was done, or
whether its function was to displace air and thus cause a vacuum as
its gases cooled. In France, too, efforts were made at this time to
produce a gunpowder engine. In 1678 a Jean de Hautefeuille raised
water by gunpowder, but authorities differ as to whether he employed
a piston--which were then in use as applied to pumps--or whether he
burned the powder so that the gases came in actual contact with the
water. In the following year an important advance was made. Huyghens
constructed an engine having a piston and cylinder, in which gunpowder
was used to form a vacuum, the atmospheric pressure providing the
positive force to produce motion; and in 1680 he communicated to the
Academy of Sciences a paper entitled, “A new motive power by means of
gunpowder and air.”
But it was to his brilliant pupil, Denis Papin, that we are indebted
for a further step in the materialization of the steam engine. Papin
suggested the use of steam for gunpowder.
In 1680 Papin, who like Solomon de Caus had brought his scientific
conceptions to England in the hope of their furtherance, was admitted
on the recommendation of Boyle to a fellowship of the Royal Society.
After a short absence he returned to London in ’84 and filled for a
time the post of curator to the society, meeting, doubtless, in that
capacity the leading scientists of the day and coming in touch with all
the practical efforts of English inventors. During his stay here he
worked with enthusiasm at the production of a prime mover, and when he
left in ’87 for a mathematical professorship in Germany he continued
there his researches and experienced repeated failures. In a paper
published in ’88 he showed a clear conception of a reciprocating engine
actuated by atmospheric pressure, and in ’90 he suggested for the first
time the use of steam for forming the vacuum required. As water, he
wrote, has elasticity when fire has changed it into vapour, and as
cold will condense it again, it should be possible to make engines
in which, by the use of heat, water would provide the vacuum which
gunpowder had failed to give. This memorable announcement gave a clear
direction to the future development of the heat engine. Steam was the
medium best suited for utilizing the expansive power of heat generated
by the combustion of fuel; steam was the medium which, by its expansive
and contractile properties, could be made to impart a movement _de va
et vient_ to a piston. Though Papin did not succeed in putting his idea
into practical form his conception was of great value, and he must be
counted as one of the principal contributors to the early development
of the steam engine. His life was an accumulation of apparent failures
ending in abject poverty. To-day he is honoured by France as the
inventor of the steam engine, and at Blois a statue has been erected
and a street named to his memory.
Before the end of the century an effective engine had been produced, in
England.
In 1698 Thomas Savery, a Devonshire man, obtained a patent for “a new
invention for raising of water and occasioning motion to all sorts of
millwork by the impellent force of fire.” Before the king at Hampton
Court a model of this invention was displayed, and the importance of
the new discovery was soon realized by the landed classes; for in the
following year an act of parliament was passed for the encouragement
of the inventor and for his protection in the development of what, it
was recognized, was likely to prove of great use to the public. In the
same year Savery published a pamphlet called _The Miner’s Friend_, and
republished it, with additions, in 1702. This pamphlet contained a full
and clear description of his engine; but significance has been attached
to the omission from it of any claim that it embodied a new idea. The
omission may be accidental.
The steam engine, shown in the accompanying illustration, was simply
a pump, whose cycle of operations was as follows. Steam, admitted
into the top of a closed vessel containing water and acting directly
against the water, forced it through a pipe to a level higher than
the vessel itself. Then, the vessel being chilled and the steam in it
thereby condensed, more water was sucked into the vessel from a lower
level to fill the vacuum thus formed; this water was expelled by steam
in the same way as before, cocks being manipulated, and, eventually,
self-acting valves being placed, so as to prevent the water from
returning by the way it came. Two chambers were used, operating
alternately.
For this achievement Savery is by many regarded as the first and
true inventor. He certainly was the first to make the steam engine a
commercial success, and up and down the country it was extensively used
for pumping water and for draining mines. By others Savery was regarded
as a copyist; and indeed it is difficult to say how far originality
should be assigned him. The marquis too had claimed to raise water; his
engine had evidently acted with a pair of displacement-chambers, from
each of which alternately water was forced by steam while the other
vessel was filling. And if he did not specify or appreciate the effect
of the contractile force of the steam when condensed, yet in this
respect both inventors had been anticipated by Giovanni della Porta.
[Illustration: Steam from Boiler.
SAVERY’S ENGINE]
The marquis had a violent champion in Dr. Desaguliers, who in his
_Experimental Philosophy_, published in 1743, imputed disreputable
conduct to the later inventor. “Captain Savery,” said the doctor,
“having read the Marquis of Worcester’s book, was the first who put
into practice the raising of water by fire. His engine will easily
appear to have been taken from the Marquis of Worcester; though Captain
Savery denied it, and the better to conceal the matter, bought all the
Marquis of Worcester’s books that he could purchase in Pater-Noster
Row and elsewhere, and burned them in the presence of the gentleman
his friend, who told me this. He said that he found out the power of
steam by chance, and invented the following story to persuade people to
believe it, viz. that having drunk a flask of Florence at a tavern, and
thrown the empty flask upon the fire, he called for a bason of water to
wash his hands, and perceiving that the little wine left in the flask
had filled the flask with steam, he took the flask by the neck and
plunged the mouth of it under the surface of the water in the bason,
and the water in the bason was immediately driven up into the flask by
the pressure of the air. Now, he never made such an experiment then,
nor designedly afterwards, which I shall thus prove,” etc. etc.
Other writers saw no good reason for depriving the captain of the title
of inventor. With reference to the book-burning allegation, the only
evidence tending to substantiate it lay in the fact that the book “on
a sudden became very scarce, and but few copies of it were afterwards
seen, and then only in the libraries of the curious.”[74] It has been
remarked, also, that Desaguliers was himself to some extent a rival
claimant, several improvements, such as the substitution of jet for the
original surface condensation being due to him; and that this fact gave
a palpable bias to his testimony on the work of others.
In recent years the claims of Savery have been upheld, as against
those of the marquis, by a writer who argued, not only that the engine
of the marquis had never passed the experimental stage, but that no
counter-claim was made by his successors at the time Savery produced
his engine and obtained his patent. “Although a patent for ninety-nine
years (from 1663 to 1762) was granted the marquis, yet Captain Savery
and his successors under his patents which extended for thirty-five
years (from 1698 to 1733) compelled every user of Newcomen’s and other
steam engines to submit to the most grinding terms and no one attempted
to plead that Savery’s patents were invalidated by the Marquis of
Worcester’s prior patents.”[75]
By the admirers of Papin it has been claimed that it was from him that
Savery received his idea. “After having minutely compared Savery’s
machine,” says a biographer of Papin, “one arrives at the conviction
that _Savery discovered nothing_. He had borrowed from Solomon de Caus
the use of steam as a motive force, perfected by the addition of a
second chamber; from Papin, the condensation of the steam.... And as
for the piston, borrowed ten years later by Newcomen, that was wholly
Papin’s.”[76]
Suppose it true; even so, his countrymen would always think great
credit attaches to Savery for his achievement.
His engine, though used extensively for lifting water through small
distances, was exceedingly wasteful of fuel, nor could it be used
conveniently for pumping out mines or for other purposes in which a
large lift was required. The lift or “head” was directly proportional
to the steam pressure. Efforts to improve the lift by augmenting the
steam pressure resulted in endless accidents and discouragement; the
solder of the engine melted when steam of a higher pressure was used,
the joints blew open and the chambers burst.
Living at Dartmouth, within some fifteen miles of Savery’s home, were
two men, Newcomen, an ironmonger, and Cawley, a glazier. These two had,
doubtless, every opportunity of seeing Savery’s engine at work. They
appreciated its limitations and defects, and, undertaking the task of
improving it, they so transformed the steam engine that within a short
time their design had almost entirely superseded the more primitive
form. Here, too, it might be said that they invented nothing. The merit
of their new machine consisted in the achievement in practical form
of ideas which hitherto had had scarcely more than an academic value.
The labours of others gave them valuable aid. Newcomen, it is certain,
could claim considerable knowledge of science, and though little is
known of his personality there is evidence that he had pursued for
years the object which he now achieved. He knew of the previous forms
of piston engine which had been invented. He had probably read a
translation, published in the _Philosophical Transactions_, of Papin’s
proposal for an atmospheric engine with a vacuum produced by the
condensation of steam. He obtained from Savery the idea of a separate
boiler, and other details. And where Papin had failed, Newcomen and
his partner succeeded. Their Atmospheric Steam Engine, as it was
aptly called, was produced in the year 1705, and at once proved its
superiority over the old “Miner’s Friend.” It had assumed an entirely
new form. In a large-bore vertical cylinder a brass piston was fitted,
with a leather flap round its edge and a layer of water standing on
it to form a seal against the passage of steam or air. The top of the
cylinder was open to the atmosphere, the bottom was connected by a pipe
with a spherical boiler. The piston was suspended by a chain to one end
of an overhanging timber beam, which was mounted on a brick structure
so as to be capable of oscillating on a gudgeon or axis at its middle.
One end of this beam was vertically over the piston; at the other
end was the bucket of a water-pump, also attached to a crosspiece or
“horse-head,” by means of a chain or rod. The whole machine formed a
huge structure like a pair of scales, one of which (the water-pump) was
loaded with weights so as to be slightly heavier than the other (the
steam engine).
[Illustration: NEWCOMEN’S ENGINE]
To work it, steam was generated in the boiler at a pressure slightly
greater than atmospheric. By the opening of a cock steam was admitted
to the cylinder, below the piston, which was initially at rest in its
highest position. The steam having filled the cylinder and expelled
nearly all the air, the cock was shut and the cylinder was chilled by
an external spray of cold water. Whereupon, as soon as the steam in
the cylinder began to condense, the piston, forced down by the now
unbalanced atmospheric pressure above it, began to descend. As soon as
it had completed its downward stroke steam was again admitted beneath
the piston, and, the pressure on the two sides of the piston becoming
equal, the piston began to move up again to its original position. And
so on.
This was the original Newcomen engine. Even in this primitive form it
far surpassed Savery’s in economy of fuel and in safety. It had, too,
far greater flexibility in the manner in which its power could be
applied; it could be used not only to lift a certain volume of water
through a relatively small height, but a smaller volume through a
greater height: which was a desideratum in the case of deep mines like
those of Cornwall. In 1720 an engine was erected at Wheal Fortune mine
having a cylinder nearly four feet in diameter and drawing water, at
fifteen strokes a minute, from a depth of 180 feet.
Yet it was apparent that the engine was in many respects inefficient.
The cocks, for instance, which controlled the motion of the piston
had to be opened and shut by a man. Sometimes he let the piston rise
too far, in fact, right out of the cylinder; sometimes he let it down
too fast, so as to damage the engine. Again, the external spraying
of the cylinder at every stroke to induce condensation of the steam
within was an obviously clumsy and primitive operation. It was not long
before external spraying gave place to internal cooling of the steam
by the injection of water; this method being discovered, it is said,
as the result of a leaky piston allowing its sealing water to pass,
yet giving unaccountably good results. The difficulties with the cocks
were overcome by the laziness or initiative of a youth named Humphrey
Potter, who attached some strings and catches to the cocks of an engine
which he was employed to work at Wolverhampton.[77]
With these improvements the engine remained practically without
alteration for the next forty years. Its greatest sphere of usefulness
was in the northern coalfields, where cheap and abundant fuel was close
at hand. In Cornwall, until by special legislation the duty on seaborne
coal was remitted when used for Newcomen’s engine, the cost of fuel
proved a great obstacle to its use.
§
In 1764 James Watt, an instrument maker employed on work for Glasgow
College, was given the task of repairing a working model of a Newcomen
engine.
A man of serious and philosophical mind, an intimate friend of
Professor Robison, the physicist, and acquainted with the famous
Dr. Black of Edinburgh, then in the thick of his researches on
the phenomena of latent heat, Watt often discussed with these two
scientists the possibility of improving the steam engine; which
apparatus was still only employed for the purpose of pumping water,
and which was so clumsy and so wasteful of fuel as to be comparatively
little used. To this end he was induced to try some experiments on
the production and condensation of steam. The results of these, and
a knowledge of the newly discovered phenomenon of latent heat,[78]
convinced him that the existing cycle of operations in the engine was
fundamentally inefficient, and that improvement was to be sought in the
engine itself rather than in the boiler, which was the element which
was receiving most attention from contemporary investigators.
In particular, he clearly discerned the thermal inefficiency of the
Newcomen engine: the waste of heat involved in alternately heating
and cooling the large metal cylinder, which absorbed such immense
quantities of fuel. Watt’s first idea was, to lag the cylinder in wood
so as to prevent all outward radiation. But the result of a trial of
a lagged cylinder was disappointing. A gain was certainly obtained
in that the steam, when admitted to the cylinder, did not require to
raise by partial condensation the temperature of the walls; it exerted
its expansive force at once and the piston rose. But on the other hand
much greater difficulty was experienced in condensing it when a vacuum
was required, for the down stroke. Moreover it was observed that an
increase in the amount of injection water only made matters worse.
Watt was faced with a dilemma, and he overcame it by a series of
studies in the properties of steam which constitute, perhaps, the
highest achievement of this workman-philosopher.
Out of all his experiments two conclusions were drawn by him; first,
that the lower the temperature of condensation of steam the more
perfect the vacuum thereby formed; second, that the temperature of
the cylinder should be as nearly as possible equal to that of the
steam admitted to it. In Newcomen’s engine these two conditions
were obviously incompatible, and the problem was,--how could they
be reconciled? Early in 1765, while walking one Sunday afternoon in
Glasgow Green the idea flashed upon him of condensing the steam in a
separate vessel. The steam was generated in a separate vessel, why not
produce the vacuum separately? With a view to trying this effect he
placed a hollow air-tight chest beneath the steam cylinder, connected
with it by a pipe having a stop-cock in it. This new or lower vessel
was immersed in a cistern of cold water. Upon trial being made, it
was found that by this simple contrivance as perfect a vacuum as
desired was produced; the speed of the engine was greatly increased,
the expenditure of fuel radically reduced, the walls of the steam
cylinder were maintained at a high and constant temperature, and the
whole arrangement promised great success. The new vessel Watt called a
Condenser.
Fresh difficulties now arose. As the engine worked, the condenser
gradually filled with the condensed steam and had to be emptied
periodically. The water in which it was immersed became so hot, by
absorbing the heat of the steam, that it frequently required changing.
Watt promptly called in aid two new auxiliaries, two organs whose
motion was derived from the main beam of the engine: the Air Pump
and the Circulating Pump. By these expedients the action of the
condenser was rendered satisfactory, and an engine resulted which had a
fuel-consumption less than half that of Newcomen’s engine.
Much, he saw, yet remained to be done to obtain economical expenditure
of steam. In particular the open-topped cylinder, whose walls were
chilled at every descent of the piston by contact with atmospheric air,
was an obvious source of inefficiency. He therefore determined not
to expose the walls to the atmosphere at all, but to enclose all the
space above the piston; and, thinking thus, he conceived the idea of
replacing the air above the piston by steam, an equally powerful agent.
The cylinder he proposed to maintain at a constant high temperature by
means of a layer of hot steam with which he encased it, which he called
a steam jacket. And so the atmospheric engine as left by Newcomen
evolved into the _single-acting steam engine_ of Watt;--an engine in
which steam was still used below the piston, only to displace air
and provide a vacuized space for the downward motion of the piston;
but in which steam now acted positively above the piston, in lieu
of atmospheric air, to drive it down. It was still a sufficiently
primitive form of prime mover. The piston was still lifted by the
counterweight at the other end of the timber cross-beam; the engine had
not yet developed the organs necessary for producing a satisfactory
rotary motion. This step was shortly to follow.
In 1769 Watt obtained his patent for the “double impulse,” as it
was called; and by this step, by the transition from a single- to a
double-acting engine, the possibilities of such machines for every
variety of application first came into general view. This stage of
the development showed to the full the ingenuity of Watt’s mechanical
mind. By the invention of the slide-valve he distributed steam to
the top and to the bottom of the cylinder, and in appropriate phase
with these actions opened the two ends to the condenser; so that the
piston was actuated positively and by an equal force on both up and
down strokes. The chain by which the piston had been suspended was no
longer adequate; it was replaced by a rod. A straight-line motion was
required for the top end of the rod; so he formed a rack, to gear with
the circular end or horse-head of the beam. But this noisy mechanism
was soon superseded by another contrivance, the beautifully simple
“parallel motion,” in which two circular motions are combined to
produce one which is rectilinear. This was patented in ’84.
Four years before this, that ancient mechanism the crank and connecting
rod had been applied, together with a flywheel, to transform the
reciprocating motion of a steam engine into a rotary motion; and the
non-possession of this invention of James Pickard’s proved for a time a
stumbling-block to Watt in his further development of his engine. Watt
would have nothing to do with it. By now he had joined his fortunes
with those of Mr. Boulton, of Soho, Birmingham, a man of great business
ability, in conjunction with whom he was engaged in constructing
engines in large numbers to suit the varying conditions of the mines in
Cornwall and the North. Considerable ingenuity was expended by him in
trying to circumvent the troublesome crank of Pickard, and many devices
were produced, the most noteworthy being the “sun-and-planet wheels,”
which enabled him with some sacrifice of simplicity to obtain the
rotary motion desired.
Watt seemed to be borne along by the momentum of his own discoveries;
every inquiry yielded him valuable reward. For some time he had studied
the possibility of reducing the violence with which the piston, now
positively steam-driven on both sides, came to the end of its stroke.
This problem led him to the discovery of the advantage of using steam
expansively: of cutting off the inflow of steam before the piston had
travelled more than a fraction of its stroke, and letting its inherent
elastic force impel it through the remainder of its journey, the
steam meanwhile expanding and thus exerting a continuously decreasing
force. Later came the throttle valve, and the centrifugal governor for
controlling the speed of rotating engines; there was no end to his
ingenuity. And so complete was his inquiry into the possible sources
of improvement of the steam engine, that he even considered means of
regulating the force which the piston exerted on the crank throughout
its working stroke, a force which was compounded of the steam pressure
itself and of the mass-acceleration of the piston and other moving
parts.
Another cardinal invention followed: the Indicator. The principle of
the indicator is now applied to every form and kind of piston engine.
It is a reproduction on a small scale of the essential part of the
engine itself; a small piston, held by a spring and moving in a
cylinder connected by a pipe with the cylinder of the engine itself,
shows by the degree of compression imparted to the spring the gaseous
pressure actually present at any moment in the engine cylinder. By
recording the position of the indicator piston on a paper wrapped round
a rotating drum whose motion represents the motion of the engine’s
piston, a diagram is obtained which by its area measures the work done
by the steam during the stroke of the engine.
This instrument was designed by Watt to give his firm some standard
of work which would serve as a basis for the power of each engine,
on which to charge their customers; their engines being sold by the
horse-power. But its usefulness far exceeded the immediate purpose
for which it was produced. Its diagram, to the eye of an expert,
gave valuable information in respect of the setting of the valves,
the tightness of the piston, the dryness of the steam, the degree of
vacuum in the condenser, and, generally, of the state of efficiency of
the engine. “It would be difficult to exaggerate the part which this
little instrument has played in the evolution of the steam engine. The
eminently philosophic notion of an indicator diagram is fundamental
in the theory of thermodynamics; the instrument itself is to the steam
engineer what the stethoscope is to the physician, and more, for with
it he not only diagnoses the ailments of a faulty machine, whether in
one or another of its organs, but gauges its power in health.”[79]
§
We have now traced the evolution of the steam engine up to the time
when it was first adapted to the propulsion of war-vessels. There we
must leave it. In a later chapter we shall consider the evolution of
the propelling machinery in its relation, especially, to the military
qualities of ships. A few observations will be sufficient to illustrate
the conditions, as to design, practice, and material, under which the
steam engine made its appearance in the royal navy.
After the death of Watt all improvement of steam machinery was
strenuously opposed by the combined force of prejudice and vested
interest. The great Watt himself had set his face against the use
of high-pressure steam, and, such was the lingering force of his
authority, years passed before the general public gave assent to the
advances made by his talented successors--Hornblower, Woolf, Evans,
and Trevithick. Before the end of the eighteenth century the first
steps had been made to use the force of steam for driving ships.
Before Trafalgar was fought steam engines had made their appearance
in the royal dockyards. Then there was a pause; and many years passed
by before steam propulsion was admitted to be a necessity for certain
classes of war-vessels.
An interesting account of the state of design and practice as it
existed on ship-board in the year of Queen Victoria’s accession is
given by Commander Robert Otway, R.N., in his treatise on _Steam
Navigation_. Low-pressure principles are still in vogue; steam is
generated still, at a pressure not exceeding three pounds per square
inch, in rectangular boilers of various forms according to the fancy
of the maker, scarcely two being alike. The engines are also of
varying forms, every size, variety, and power being deemed suitable
for similar vessels. They are amazingly ponderous: weigh about twelve
hundredweight, and the boilers eight hundredweight, to the horsepower.
The engines of all makers exhibit the greatest variations in the
relative dimensions of their various parts: one firm embodies a massive
frame and light moving rods and shafts, another adopts massive rods and
shafts, and supports them within the lightest framework. The author
advocates a correct design and a “total dispensation of all superfluous
ornament.”
[Illustration: CONNECTING ROD
From Otway]
Already, however, following the example of the Cornish mines, the
builders of steam vessels were at this time beginning to adopt
high-pressure steam, generated at a pressure of ten to fifteen pounds
per square inch in cylindrical boilers, and working expansively--“doing
work in the cylinder by its elasticity alone”--before returning to
the jet condenser. This improvement, strenuously opposed by orthodox
engineers as being unsafe for ship practice, was introduced first
into the Packet Establishment at Falmouth, and then, tardily, into
Government steamers. It gave a gain in economy measured by the saving
of “thousands of bushels of coal per month.” Steam engines working
on the low-pressure system used from nine to twelve pounds of coal
per hour, for each horse-power. These engines were carried in vessels
“built on the scantling of 10-ton brigs,” of great draught and of
such small coal capacity--about 35 tons, on an average--that when
proceeding out of home waters “they were burthened with, at the least,
four days’ more fuel, _on their decks_ (top hamper), in addition to
that which already filled up their coal-boxes below.” Boilers emitted
black clouds of smoke at sea. In harbour the paddle-wheels had to be
turned daily, if but a few float-boards only, by the united force of
the crew. “Coaling ship” was carried out with the help of convicts from
the hulks:--“pampered delinquents,” observes the author, “whose very
movements are characteristic of their moral dispositions--being thieves
of time; for their whole day’s duty is not worth an hour’s purchase.”
In these unattractive circumstances the steam engine, most wonderful
contrivance of the brain and hand of man, presented itself for
embodiment in the navy, by the personnel of which it was regarded, not
without reason, as an unmitigated evil.