Newcomen's engine in another respect. To keep it at work, one man was
required to attend the fire, and another to turn alternately the two
cocks, one admitting the steam into the cylinder, the other admitting
the jet of cold water to condense it. The turning of these cocks was
easy work, usually performed by a boy. It was, however, a very
monotonous duty, though requiring constant attention. To escape the
drudgery and obtain an interval for rest or perhaps for play, a boy
named Humphrey Potter, who turned the cocks, set himself to discover
some method of evading his task. He must have been an ingenious boy, as
is clear from the arrangement he contrived with this object. Observing
the alternate ascent and descent of the beam above his head, he
bethought him of applying the movement to the alternate raising and
lowering of the levers which governed the cocks. The result was the
contrivance of what he called the _scoggan_ (meaning presumably the
loafer or lazy boy), consisting of a catch worked by strings from the
beam of the engine. This arrangement, when tried, was found to answer
the purpose intended. The action of the engine was thus made automatic;
and the arrangement, though rude, not only enabled Potter to enjoy his
play, but it had the effect of improving the working power of the engine
itself; the number of strokes which it made being increased from six or
eight to fifteen or sixteen in the minute. This invention was afterward
greatly improved by Mr. Henry Beighton, of Newcastle-on-Tyne, who added
the plug-rod and hand-gear. He did away with the catches and strings of
the boy Potter's rude apparatus, and substituted a rod suspended from
the beam, which alternately opened and shut the tappets attached to the
steam and injection cocks.
Thus, step by step, Newcomen's engine grew in power and efficiency, and
became more and more complete as a self-acting machine. It will be
observed that, like all other inventions, it was not the product of any
one man's ingenuity, but of many. One contributed one improvement, and
another another. The essential features of the atmospheric engine were
not new. The piston and cylinder had been known as long ago as the time
of Hero. The expansive force of steam and the creation of a vacuum by
its condensation had been known to the Marquis of Worcester, Savery,
Papin, and many more. Newcomen merely combined in his machine the result
of their varied experience; and, assisted by the persons who worked with
him, down to the engine-boy Potter, he advanced the invention several
important stages; so that the steam-engine was no longer a toy or a
scientific curiosity, but had become a powerful machine capable of doing
useful work.
JAMES WATT AND THE STEAM-ENGINE.
It was in the year 1759 that Robison[9] first called the attention of
his friend Watt to the subject of the steam-engine. Robison was then
only in his twentieth, and Watt in his twenty-third year. Robison's
idea was that the power of steam might be advantageously applied to the
driving of wheel-carriages; and he suggested that it would be the most
convenient for the purpose to place the cylinder with its open end
downwards to avoid the necessity of using a working-beam. Watt admits
that he was very ignorant of the steam-engine at the time; nevertheless,
he began making a model with two cylinders of tin plate, intending that
the pistons and their connecting-rods should act alternately on two
pinions attached to the axles of the carriage-wheels. But the model,
being slightly and inaccurately made, did not answer his expectations.
Other difficulties presented themselves, and the scheme was laid aside
because Robison left Glasgow to go to sea. Indeed, mechanical science
was not yet ripe for the locomotive. Robison's idea had, however,
dropped silently into the mind of his friend, where it grew from day to
day, slowly and at length fruitfully.
At his intervals of leisure and in the quiet of his evenings, Watt
continued to prosecute his various studies. He was shortly attracted by
the science of chemistry, then in its infancy. Dr. Black was at that
time occupied with the investigations which led to his discovery of the
theory of latent heat, and it is probable that his familiar
conversations with Watt on the subject induced the latter to enter upon
a series of experiments with the view of giving the theory some
practical direction. His attention again and again reverted to the
steam-engine, though he had not yet seen even a model of one. Steam was
as yet almost unknown in Scotland as a working power. The first engine
was erected at Elphinstone Colliery, in Stirlingshire, about the year
1750; and the second more than ten years later, at Govan Colliery, near
Glasgow, where it was known by the startling name of "The Firework."
This had not, however, been set up at the time Watt had begun to inquire
into the subject. But he found that the college possessed the model of a
Newcomen engine for the use of the Natural Philosophy class, which had
been sent to London for repair. On hearing of its existence, he
suggested to his friend Dr. Anderson, Professor of Natural Philosophy,
the propriety of getting back the model; and a sum of money was placed
by the Senatus at the professor's disposal, "to recover the steam-engine
from Mr. Sisson, instrument-maker in London."
In the mean time Watt sought to learn all that had been written on the
subject of the steam-engine. He ascertained from Desaguliers, Switzer,
and other writers, what had been accomplished by Savery, Newcomen,
Beighton, and others; and he went on with his own independent
experiments. His first apparatus was of the simplest possible kind. He
used common apothecaries' phials for his steam reservoirs, and canes
hollowed out for his steam-pipes. In 1761 he proceeded to experiment on
the force of steam by means of a small Papin's digester and a syringe.
The syringe was only the third of an inch in diameter, fitted with a
solid piston; and it was connected with the digester by a pipe furnished
with a stopcock, by which the steam was admitted or shut off at will. It
was also itself provided with a stopcock, enabling a communication to be
opened between the syringe and the outer air to permit the steam in the
syringe to escape. The apparatus, though rude, enabled the experimenter
to ascertain some important facts. When the steam in the digester was
raised and the cock turned, enabling it to rush against the lower side
of the piston, he found that the expansive force of the steam raised a
weight of fifteen pounds, with which the piston was loaded. Then on
turning on the cock and shutting off the connection with the digester at
the same time that a passage was opened to the air, the steam was
allowed to escape, when the weight upon the piston, being no longer
counteracted, immediately forced it to descend.
Watt saw that it would be easy to contrive that the cocks should be
turned by the machinery itself with perfect regularity. But there was an
objection to this method. Water is converted into vapor as soon as its
elasticity is sufficient to overcome the weight of the air which keeps
it down. Under the ordinary pressure of the atmosphere water acquires
this necessary elasticity at 212°; but as the steam in the digester was
prevented from escaping, it acquired increased heat, and by consequence
increased elasticity. Hence it was that the steam which issued from the
digester was not only able to support the piston and the air which
pressed upon its upper surface, but the additional load with which the
piston was weighted. With the imperfect mechanical construction,
however, of those days, there was a risk lest the boiler should be burst
by the steam, which was apt to force its way through the ill-made joints
of the machine. This, conjoined with the great expenditure of steam on
the high-pressure system, led Watt to abandon the plan; and the
exigencies of his business for a time prevented him from pursuing his
experiments.
At length the Newcomen model arrived from London; and in 1763 the little
engine, which was destined to become so famous, was put into the hands
of Watt. The boiler was somewhat smaller than an ordinary teakettle. The
cylinder of the engine was only of two inches diameter and six inches
stroke. Watt at first regarded it as merely "a fine plaything." It was,
however, enough to set him upon a track of thinking which led to the
most important results. When he had repaired the model and set it to
work, he found that the boiler, though apparently large enough, could
not supply steam in sufficient quantity, and only a few strokes of the
piston could be obtained, when the engine stopped. The fire was urged by
blowing, and more steam was produced; but still it would not work
properly. Exactly at the point at which another man would have abandoned
the task in despair, the mind of Watt became thoroughly roused.
"Everything," says Professor Robison, "was to him the beginning of a new
and serious study; and I knew that he would not quit it till he had
either discovered its insignificance or had made something of it." Thus
it happened with the phenomena presented by the model of the
steam-engine. Watt referred to his books, and endeavored to ascertain
from them by what means he might remedy the defects which he found in
the model; but they could tell him nothing. He then proceeded with an
independent course of experiments, resolved to work out the problem for
himself. In the course of his inquiries he came upon a fact which, more
than any other, led his mind into the train of thought which at last
conducted him to the invention of which the results were destined to
prove so stupendous. This fact was the existence of latent heat.
In order to follow the track of investigation pursued by Watt, it is
necessary for a moment to revert to the action of the Newcomen
pumping-engine. A beam, moving upon a centre, had affixed to one end of
it a chain attached to the piston of the pump, and at the other a chain
attached to a piston that fitted into the steam-cylinder. It was by
driving this latter piston up and down the cylinder that the pump was
worked. To communicate the necessary movement to the piston, the steam
generated in a boiler was admitted to the bottom of the cylinder,
forcing out the air through a valve, where its pressure on the under
side of the piston counterbalanced the pressure of the atmosphere on its
upper side. The piston, thus placed between two equal forces, was drawn
up to the top of the cylinder by the greater weight of the pump-gear at
the opposite extremity of the beam. The steam, so far, only discharged
the office of the air it displaced; but if the air had been allowed to
remain, the piston once at the top of the cylinder could not have
returned, being pressed as much by the atmosphere underneath as by the
atmosphere above it. The steam, on the contrary, which was admitted by
the exclusion of air, _could be condensed_, and a vacuum created, by
injecting cold water through the bottom of the cylinder. The piston,
being now unsupported, was forced down by the pressure of the atmosphere
on its upper surface. When the piston reached the bottom, the steam was
again let in, and the process was repeated. Such was the engine in
ordinary use for pumping water at the time that Watt began his
investigations.
Among his other experiments, he constructed a boiler which showed by
inspection the quantity of water evaporated in any given time, and the
quantity of steam used in every stroke of the engine. He was astonished
to discover that a _small_ quantity of water in the form of steam heated
a large quantity of cold water injected into the cylinder for the
purpose of cooling it; and upon further examination he ascertained that
steam heated six times its weight of cold water to 212°, which was the
temperature of the steam itself. "Being struck with this remarkable
fact," says Watt, "and not understanding the reason of it, I mentioned
it to my friend Dr. Black, who then explained to me his doctrine of
latent heat, which he had taught for some time before this period (the
summer of 1764); but having myself been occupied by the pursuits of
business, if I had heard of it I had not attended to it, when I thus
stumbled upon one of the material facts by which that beautiful theory
is supported."
When Watt found that water in its conversion into vapor became such a
reservoir of heat, he was more than ever bent on economizing it; for the
great waste of heat involving so heavy a consumption of fuel was felt to
be the principal obstacle to the extended employment of steam as a
motive power. He accordingly endeavored, with the same quantity of fuel,
at once to increase the production of steam and to diminish its waste.
He increased the heating surface of the boiler by making flues through
it; he even made his boiler of wood, as being a worse conductor of heat
than the brickwork which surrounds common furnaces; and he cased the
cylinders and all the conducting pipes in materials which conducted heat
very slowly. But none of these contrivances were effectual; for it
turned out that the chief expenditure of steam, and consequently of
fuel, in the Newcomen engine, was occasioned by the reheating of the
cylinder after the steam had been condensed, and the cylinder was
consequently cooled by the injection into it of the cold water. Nearly
four fifths of the whole steam employed was condensed on its first
admission, before the surplus could act upon the piston. Watt therefore
came to the conclusion that to make a perfect steam-engine it was
necessary that _the cylinder should be always as hot as the steam that
entered it_; but it was equally necessary that the steam should be
condensed when the piston descended, nay, that it should be cooled down
below 100°, or a considerable amount of vapor would be given off, which
would resist the descent of the piston, and diminish the power of the
engine. Thus the cylinder was never to be at a less temperature than
212°, and yet at each descent of the piston it was to be less than
100°,--conditions which, on the very face of them, seemed to be wholly
incompatible.
Though still occupied with his inquiries and experiments as to steam,
Watt did not neglect his proper business, but was constantly on the
look-out for improvements in instrument-making. A machine which he
invented for drawing in perspective proved a success; and he made a
considerable number of them to order, for customers in London as well as
abroad. He was also an indefatigable reader, and continued to extend his
knowledge of chemistry and mechanics by perusal of the best books on
these sciences.
Above all subjects, however, the improvement of the steam-engine
continued to keep the fastest hold upon his mind. He still brooded over
his experiments with the Newcomen model, but did not seem to make much
way in introducing any practical improvement in its mode of working. His
friend Robison says he struggled long to condense with sufficient
rapidity without injection, trying one experiment after another, finding
out what would _not_ do, and exhibiting many beautiful specimens of
ingenuity and fertility of resource. He continued, to use his own words,
"to grope in the dark, misled by many an _ignis fatuus_." It was a
favorite saying of his that "Nature has a weak side, if we can only find
it out;" and he went on groping and feeling for it, but as yet in vain.
At length light burst upon him, and all at once the problem over which
he had been brooding was solved.
THE SEPARATE CONDENSER.
One Sunday afternoon, in the spring of 1765, he went to take an
afternoon walk on the Green, then a quiet grassy meadow used as a
bleaching and grazing ground. On week days the Glasgow lasses came
thither with their largest kail-pots to boil their clothes in; and
sturdy queans might be seen, with coats kilted, trampling blankets in
their tubs. On Sundays the place was comparatively deserted; and hence
Watt, who lived close at hand, went there to take a quiet afternoon
stroll. His thoughts were as usual running on the subject of his
unsatisfactory experiments with the Newcomen engine, when the first idea
of the separate condenser suddenly flashed upon his mind. But the
notable discovery is best told in his own words, as related to Mr.
Robert Hart, many years after:--
"I had gone to take a walk on a fine Sabbath afternoon. I had entered
the Green by the gate at the foot of Charlotte Street, and had passed
the old washing-house. I was thinking upon the engine at the time, and
had gone as far as the herd's house, when the idea came into my mind
that as the steam was an elastic body, it would rush into a vacuum, and
if a communication were made between the cylinder and an exhausted
vessel, it would rush into it and might be then condensed without
cooling the cylinder. I then saw that I must get rid of the condensed
steam and the injection water if I used a jet, as in Newcomen's engine.
Two ways of doing this occurred to me. First, the water might be run off
by a descending pipe, if an off-let could be got at the depth of 35 or
36 feet, and any air might be extracted by a small pump. The second was
to make the pump large enough to extract both water and air." He
continued: "I had not walked farther than the Golf-house when the whole
thing was arranged in my mind."
Great and prolific ideas are almost always simple. What seems impossible
at the outset appears so obvious when it is effected, that we are prone
to marvel that it did not force itself at once upon the mind. Late in
life Watt, with his accustomed modesty, declared his belief that if he
had excelled, it had been by chance, and the neglect of others. To
Professor Jardine he said that when it was analyzed the invention would
not appear so great as it seemed to be. "In the state," said he, "in
which I found the steam-engine, it was no great effort of mind to
observe that the quantity of fuel necessary to make it work would
forever prevent its extensive utility. The next step in my progress was
equally easy,--to inquire what was the cause of the great consumption of
fuel: this, too, was readily suggested, viz., the waste of fuel which
was necessary to bring the whole cylinder, piston, and adjacent parts
from the coldness of water to the heat of steam, no fewer than from
fifteen to twenty times in a minute." The question then occurred, How
was this to be avoided or remedied? It was at this stage that the idea
of carrying on the condensation in a separate vessel flashed upon his
mind, and solved the difficulty.
Mankind has been more just to Watt than he was to himself. There was no
accident in the discovery. It had been the result of close and
continuous study; and the idea of the separate condenser was merely the
last step of a long journey, a step which could not have been taken
unless the road which led to it had been traversed. Dr. Black says,
"This capital improvement flashed upon his mind at once, and filled him
with rapture,"--a statement which, in spite of the unimpassioned nature
of Watt, we can readily believe.
On the morning following his Sunday afternoon's walk on Glasgow Green,
Watt was up betimes, making arrangements for a speedy trial of his new
plan. He borrowed from a college friend a large brass syringe, an inch
and a third in diameter, and ten inches long, of the kind used by
anatomists for injecting arteries with wax previous to dissection. The
body of the syringe served for a cylinder, the piston-rod passing
through a collar of leather in its cover. A pipe connected with the
boiler was inserted at both ends for the admission of steam, and at the
upper end was another pipe to convey the steam to the condenser. The
axis of the stem of the piston was drilled with a hole, fitted with a
valve at its lower end, to permit the water produced by the condensed
steam on first filling the cylinder to escape. The first condenser made
use of was an improvised cistern of tinned plate, provided with a pump
to get rid of the water formed by the condensation of the steam, both
the condensing-pipes and the air-pump being placed in a reservoir of
cold water.
"The steam-pipe," says Watt, "was adjusted to a small boiler. When the
steam was produced, it was admitted into the cylinder, and soon issued
through the perforation of the rod and at the valve of the condenser;
when it was judged that the air was expelled, the steam-cock was shut,
and the air-pump piston-rod was drawn up, which leaving the small pipes
of the condenser in a state of vacuum, the steam entered them, and was
condensed. The piston of the cylinder immediately rose, and lifted a
weight of about eighteen pounds, which was hung to the lower end of the
piston-rod. The exhaustion-cock was shut, the steam was re-admitted
into the cylinder, and the operation was repeated. The quantity of steam
consumed and the weights it could raise were observed, and, excepting
the non-application of the steam-case and external covering, the
invention was complete in so far as regarded the savings of steam and
fuel."
COMPLETING THE INVENTION.
But although the invention was complete in Watt's mind, it took him many
long and laborious years to work out the details of the engine. His
friend Robison, with whom his intimacy was maintained during these
interesting experiments, has given a graphic account of the difficulties
which he successively encountered and overcame. He relates that on his
return from the country, after the college vacation in 1765, he went to
have a chat with Watt and communicate to him some observations he had
made on Desaguliers' and Belidor's account of the steam-engine. He went
straight into the parlor, without ceremony, and found Watt sitting
before the fire looking at a little tin cistern which he had on his
knee. Robison immediately started the conversation about steam; his
mind, like Watt's, being occupied with the means of avoiding the
excessive waste of heat in the Newcomen engine. Watt all the while kept
looking into the fire, and after a time laid down the cistern at the
foot of his chair, saying nothing. It seems that Watt felt rather
nettled that Robison had communicated to a mechanic of the town a
contrivance which he had hit upon for turning the cocks of his engine.
When Robison therefore pressed his inquiry, Watt at length looked at him
and said briskly, "You need not fash yourself any more about that, man.
I have now made an engine that shall not waste a particle of steam. It
shall all be boiling hot,--ay, and hot water injected, if I please." He
then pushed the little tin cistern with his foot under the table.
Robison could learn no more of the new contrivance from Watt at that
time; but on the same evening he accidentally met a mutual acquaintance,
who, supposing he knew as usual the progress of Watt's experiments,
observed to him, "Well, have you seen Jamie Watt?" "Yes." "He'll be in
fine spirits now with his engine?" "Yes," said Robison, "very fine
spirits." "Gad!" said the other, "the separate condenser's the thing;
keep it but cold enough, and you may have a perfect vacuum, whatever be
the heat of the cylinder." This was Watt's secret, and the nature of the
contrivance was clear to Robison at once.
It will be observed that Watt had not made a secret of it to his other
friends. Indeed, Robison himself admitted that one of Watt's greatest
delights was to communicate the results of his experiments to others,
and set them upon the same road to knowledge with himself; and that no
one could display less of the small jealousy of the tradesman than he
did. To his intimate friend Dr. Black he communicated the progress made
by him at every stage. The Doctor kindly encouraged him in his
struggles, cheered him in his encounter with difficulty, and, what was
of still more practical value at the time, helped him with money to
enable him to prosecute his invention. Communicative though Watt was
disposed to be, he learnt reticence when he found himself exposed to the
depredations of the smaller fry of inventors. Robison says that had he
lived in Birmingham or London at the time, the probability is that some
one or other of the numerous harpies who live by sucking other people's
brains would have secured patents for his more important inventions, and
thereby deprived him of the benefits of his skill, science, and labor.
As yet, however, there were but few mechanics in Glasgow capable of
understanding or appreciating the steam-engine; and the intimate friends
to whom he freely spoke of his discovery were too honorable to take
advantage of his confidence. Shortly after Watt communicated to Robison
the different stages of his invention, and the results at which he had
arrived, much to the delight of his friend.