water has risen into and filled the force-pipe, it fills also a
little cistern, and by that means fills another pipe, called the
condensing-pipe, which may be turned either way, over any of the
receivers, when either is thoroughly heated by, the steam, to condense
it within, thereby producing a vacuum, which absorbs the water out
of the well into the receiver, on the principle of a syphon. Also a
little above the cistern goes another pipe to convey the water from the
force-pipe into the lesser boiler, for the purpose of replenishing
the great boiler, when the water in it begins to be almost consumed.
Whenever there is occasion for this, the cock is to be turned which
communicates between the force-pipe and the lesser boiler, to close
it effectually; at the same time having put a little fire beneath the
small boiler, which will grow hot; its own steam, which has no vent to
escape, pressing on its surface, will force the water up another pipe,
through an aperture in the great boiler, and so long will it run, till
the surface of the water gets so low as to be beneath the bottom of the
pipe of communication--then the steam and water running together, will
cause the valve (called a clack) to strike, which will intimate to the
operator that it has discharged itself into the greater boiler, and
carried in as much water as is then necessary; after which, by turning
a cock, as much fresh water is let in as may be necessary; and then, by
turning another cock, new fresh water is let out of a recipient into
the less boiler as before; and thus the engine is supplied without fear
of decay, or any delay in the operations; and proper attention in the
workmen is only necessary to prevent disorder in a machine so expensive
and complicated.
Also, to know when the great boiler wants replenishing, turn the
gauge-cock; if water comes out, it does not need a supply; but if steam
alone, then the want of water is certain. The like with the cock with
which the lesser boiler is prepared for the same purpose, when the
same state will be marked by like results. In working this engine,
very little skill, and less labour is required: _Attention_ is the
chief requisite; it is only to be injured by want of due care, extreme
stupidity, or wilful neglect.
The engine described above, does not differ essentially from that first
designed by the inventor, Captain Savery; the chief alteration which
now occurs, is only in some few slight particulars. For example, the
original engine had only one boiler, and there was no ready means for
supplying it with water, to remedy the waste occasioned by evaporation
of steam, without stopping the action of the engine, whenever the
boiler was emptied to such a degree as to risk burning the vessel.
After it was replenished the machine had to remain idle till the steam
was raised, thus causing an immense loss of time; which is remedied by
the application of a second boiler.
The description of the engine formerly mentioned is transcribed from
Mr. Savery’s publication, “The Miner’s Friend,” and which had a
subsidiary boiler, with water of a boiling heat, always ready to supply
the large boiler; and the power of steam raised in it is employed to
force the water into the larger boiler, to replace the waste occasioned
by evaporation from that boiler; by this means the transposition of
the feeding water is not only speedily performed, but being itself of
a boiling heat, it is instantly ready to produce steam for carrying
on the work. There is also one more grand improvement in the modern
machine: the first engine was worked by four separate cocks, which the
operator was compelled to turn separately at every change of stroke;
if he turned them wrong, he was not only liable to damage the engine,
but he prevented its effect, and, at the same time, lost a part of
the operation: whereas, in the improved engine, the communications
are made by a double sliding valve, or, as it has since been termed,
regulator; that is, a brass plate, shaped like a fan, and moving on a
centre within the boiler, so as to slide horizontally in contact with
the under surface of the cover of the boiler, to which it is accurately
fitted by grinding, and thus, at pleasure, opens or shuts the orifices,
or entries, to the steam pipes of the two receivers alternately. This
regulator acts with less friction than a cock of equal bore, and, by
the motion of a single handle backwards, at once opens the proper steam
pipe from one receiver, and closes that which belongs to the other
receiver. Captain Savery, in his publication before noticed, describes
the uses to which this machine may be applied, besides those before
described, viz.--1, to serve water for turning all sorts of mills; 2,
for supplying palaces, noblemen and gentlemen’s houses with water, and
affording the means for extinguishing fires therein, by the water so
raised; 3, the supplying cities and towns with water; 4, draining fens
and marshes; 5, for ships; 6, for draining mines of water; and 7, for
preventing damps in mines.
Dr. Desaguliers, we conceive, ungenerously attacked Captain Savery’s
reputation, by alleging that this was not an original invention, and
that he was indebted for the first idea to the previously mentioned
plan of the Marquis of Worcester. Dr. Rees, with a generous liberality
worthy his great critical discrimination, scientific skill, and
general erudition, has, we think, ably defended the captain’s
character, by proving his ideas to have originated with himself; we
have only an opportunity to notice the most prominent features in this
justification, where Dr. Rees thus expresses himself. “We know that the
Marquis of Worcester gave no hint concerning the _contractibility or
condensation of steam, upon which all the merit of the modern engine
depends_. The Marquis of Worcester’s engine was actuated wholly by the
elastic power of steam, which he either found out, or proved by the
bursting of cannon in part filled with water; and not the least hint
that steam so expanded, is capable of being so far contracted in an
instant, as to leave the space it occupied in a vessel, and occasion,
in a great measure, a vacuum.”
Subsequent to the Marquis of Worcester’s, and Captain Savery’s original
ideas, and also, subsequent to the perfection the captain had brought
his machine to, M. Amonton, a native of France, invented a machine
which he called a fire-wheel; but it does not appear that it was ever
brought to that perfection to be conducive to real utility, although
it was certainly very ingenious.
Also, M. Papin, a native of Germany, made some pretensions to what
he alleged was an invention of his own, only it happened to appear,
unfortunately for his claim, that he was in London, and present at the
time when Captain Savery exhibited the model of his steam-engine to the
Royal Society. He made some unsuccessful experiments, by order of his
patron, the Landgrave of Hesse, which sufficiently proved that, if he
was the inventor, he did not understand the nature of his own machine.
Not long after Savery had invented his engine, Thomas Newcomen, an
ironmonger, and John Calley, a glazier, began to direct their attention
to the employment of steam as a mechanic power. Their first engine
was constructed about the year 1711. This machine still acted on the
principle of condensing the steam by means of cold water, and the
pressure of the atmosphere on the piston. It was found of great value
in pumping water from deep mines; but the mode of its construction, the
great waste of fuel, the continued cooling and heating of the cylinder,
and the limited capacities of the atmosphere in impelling the piston
downward, all tended to circumscribe its utility.
The steam-engine was in this state, when it happily attracted the
attention of Mr. Watt, to whom the merit and honour is due, of having
first rendered this invention available as a mechanical agent. We
cannot illustrate the improvements of this ingenious individual better
than by giving a short biographical sketch of him to whom the world is
so much indebted.
James Watt was born at Greenock, an extensive seaport in the west of
Scotland, on the 19th of January, 1736. His father was a merchant, and
also one of the magistrates of that town. He received the rudiments of
his education in his native place; but his health being then extremely
delicate, as it continued to be to the end of his life, his attendance
at school was not always very regular. He amply made up, however, for
what he lost in this way, by the diligence with which he pursued his
studies at home, where, without any assistance, he succeeded, at a
very early age, in making considerable proficiency in various branches
of knowledge. Even at this time it is said his favourite study was
mechanical science, to a love of which he was probably in some degree
led by the example of his grandfather and his uncle, both of whom had
been teachers of mathematics, and had left a considerable reputation
for learning and ability in that department. Young Watt, however, was
not indebted to any instruction of theirs for his own acquirements in
science, the former having died two years before, and the latter one
year after he was born. At the age of eighteen he was sent to London,
to be apprenticed to a maker of mathematical instruments; but in
little more than a year the state of his health forced him to return
to Scotland; and he never received any further instruction in his
profession. A year or two after this, however, a visit which he paid
to some relations in Glasgow, suggested to him the plan of attempting
to establish himself in that city, in the line for which he had been
educated. In 1757, he accordingly removed thither, and was immediately
appointed mathematical instrument maker to the College. In this
situation he remained for some years, during which, notwithstanding
almost constant ill health, he continued both to prosecute his
profession, and to labour in the general cultivation of his mind,
with extraordinary ardour and perseverance. Here also he enjoyed the
intimacy and friendship of several distinguished persons, who were then
members of the University, especially of the celebrated Dr. Black, the
discoverer of the principle of latent heat, and Dr. Robison, so well
known by his treatises on mechanical science, who was then a student,
and about the same age as himself. Honourable, however as his present
appointment was, and important as were many of the advantages to
which it introduced him, he probably did not find it a very lucrative
one; and therefore, in 1763, when about to marry, he removed from his
apartments in the University, to a house in the city, and entered upon
the profession of a general engineer.
For this his genius and scientific attainments most admirably
qualified him. Accordingly he soon acquired a high reputation, and
was extensively employed in making surveys and estimates for canals,
harbours, bridges, and other public works. His advice and assistance
were sought for in almost all the important improvements of this
description, which were now undertaken or proposed in his native
country. But another pursuit, in which he had been for some time
privately engaged, was destined ere long to withdraw him from this line
of exertion, and to occupy his whole mind with an object still more
worthy of its extraordinary powers.
While yet residing in the College, his attention had been directed to
the employment of steam as a mechanical agent, by some speculations of
his friend Mr. Robison, with regard to the practicability of applying
it to the movement of wheel-carriages; and he had also himself made
some experiments with Papin’s digester, with the view of ascertaining
its expansive force. He had not prosecuted the inquiry, however, so
far as to have arrived at any determinate result, when the winter
of 1763-4, a small model of Newcomen’s engine was sent him by the
Professor of Natural Philosophy, to be repaired, and fitted for
exhibition in the class. The examination of this model set Watt upon
thinking anew, and with more interest than ever, on the powers of
steam. Struck with the radical imperfections of the atmospheric engine,
he began to turn in his mind the possibility of employing steam in
mechanics, in some new manner which should enable it to work with
much more powerful effect. This idea having got possession of him,
he engaged in an extensive course of experiments, for the purpose of
ascertaining as many facts as possible with regard to the properties
of steam; and the pains he took in this investigation were rewarded
with several valuable discoveries. The rapidity with which water
evaporates he found, for instance, depended simply upon the quantity
of heat which was made to enter it; and this again, on the extent of
the surface exposed to the fire. He also ascertained the quantity of
coals necessary for the evaporation of any given quantity of water,
the heat at which water boils, under various pressures, and many other
particulars of a similar kind, which had never before been accurately
determined.
Thus prepared by a complete knowledge of the properties of the agent
with which he had to work, he next took into consideration, with a view
to their amendment, what he deemed the two great defects of Newcomen’s
engine. The first of these was the necessity arising from the method
employed to concentrate the steam, of cooling the cylinder, before
every stroke of the piston, by the water injected into it. On this
account, a much more powerful application of heat than would otherwise
have been requisite was demanded for the purpose of again heating that
vessel when it was to be refilled with steam. In fact, Watt ascertained
that there was thus occasioned, in the feeding of the machine, a waste
of not less than three-fourths of the whole fuel employed. If the
cylinder, instead of being thus cooled for every stroke of the piston,
could be permanently hot, a fourth part of the heat which had hitherto
been applied would be found sufficient to produce steam enough to fill
it. How then was this desideratum to be obtained? Savery, the first who
really constructed a working engine, and whose arrangements, as we have
already remarked, all showed a very superior ingenuity, employed the
method of throwing cold water over the outside of the vessel containing
the steam--a perfectly manageable process, but at the same time a very
wasteful one; inasmuch as every time it was repeated, it cooled not
only the steam, but the vessel also, which, therefore, had again to
be heated, by a large expenditure of fuel, before the steam could be
produced. Newcomen’s method of injecting the water into the cylinder
was a considerable improvement on this; but it was still objectionable
on the same ground, though not to the same degree; it still cooled not
only the steam, on which it was desired to produce that effect, but
also the cylinder itself, which, as the vessel in which more steam was
to be immediately manufactured, it was so important to keep hot. It
was also a very serious objection to this last mentioned plan, that
the injected water, itself, from the heat of the place into which it
was thrown, was very apt to be partly converted into steam; and the
more cold water was used, the more considerable did this creation of
new steam become. In fact, in the last of Newcomen’s engines, the
rarefaction of the vacuum was so greatly improved from this cause,
that the resistance experienced by the piston in its descent was found
to amount to about a fourth part of the whole atmospheric pressure by
which it was carried down, or, in other words, the working power of the
machine was thereby diminished one-fourth.
After reflecting for some time upon all this, it at last occurred
to Watt to consider whether it might not be possible, instead of
continuing to condense the steam in the cylinder, to contrive that
method of drawing it off, to undergo that operation in some other
vessel. This fortunate idea having presented itself to his mind, it was
not long before his ingenuity suggested to him the means of realising
it. In the course of one or two days, according to his own account, he
had all the necessary apparatus arranged in his mind. The plan which
he devised was, indeed, an extremely simple one, and on that account
the more beautiful. He proposed to establish a communication by an
open pipe, between the cylinder and another vessel, the consequence of
which evidently would be, that when the steam was admitted into the
former, it would flow into the other to fill it also. If, then, the
portion in this latter vessel only should be subjected to a condensing
process, by being brought into contact with cold water, or any other
convenient means, what would follow? Why, a vacuum would be produced
here--into that, as a vent, more steam would immediately rush from the
cylinder--that likewise would be condensed--and so the process would
go on till all the steam had left the cylinder, and a perfect vacuum
had been effected in that vessel, without so much as a drop of cold
water having touched or entered it. The separate vessel alone, or the
condenser, as Watt called it, would be cooled by the water used to
condense the steam--and that, instead of being an evil, manifestly
tended to promote and quicken the condensation. When Watt reduced his
views to the test of experiment, he found the result to answer his most
sanguine expectations. The cylinder, although emptied of its steam
for every stroke of the piston as before, was now constantly kept at
the same temperature with the steam (or 212 deg. Fahrenheit); and
the consequence was, that one-fourth of the fuel formerly required,
sufficed to feed the engine. But besides this most important saving in
the expense of maintaining the engine, its power was greatly increased
by the most perfect vacuum produced in the new construction, in which
the condensing water, being no longer admitted within the cylinder,
could not, as before, create new steam there while displacing the old.
Such, then, was the remedy by which the genius of this great inventor
effectually cured the first and most serious defect of the old
apparatus. In carrying his ideas into execution, he encountered, as
was to be expected, many difficulties, arising principally from the
impossibility of realising theoretical perfection of structure with
such materials as human art is obliged to work with; but his ingenuity
and perseverance overcame every obstacle. One of the things which cost
him the greatest trouble was, how to fit the piston so exactly to the
cylinder, as, without affecting the freedom of its motion, to prevent
the passage of the air between the two. In the old engine this end had
been obtained by covering the piston with a small quantity of water,
the dripping down of which into the space below, where it merely mixed
with the stream introduced to effect the condensation, was of little or
no consequence. But in the new construction, the superiority of which
consisted in keeping this receptacle for the steam always both hot and
dry, such an effusion of moisture, although in very small quantities,
would have occasioned material inconvenience. The air alone, besides,
which in the old engine followed the piston in its descent, acted with
considerable effect in cooling the lower part of the cylinder. His
attempts to overcome this difficulty, while they succeeded in that
object, conducted Watt also to another improvement, which effected the
complete removal of what we have called the second radical imperfection
of Newcomen’s engine, namely, its non-employment for a moving power, of
the expansive force of steam. The effectual way it occurred to him of
preventing any air from escaping into the part of the cylinder below
the piston, would be to dispense with the use of that element above
the piston, and to substitute there likewise the same contrivance as
below, of alternate steam and a vacuum. This was, of course, to be
accomplished by merely opening communications from the upper part of
the cylinder to the boiler on the one hand, and the condenser on the
other, and forming it at the same time into an air-tight chamber, by
means of a cover, with only a hole in it to admit the rod or shank
of the piston, which might, besides, without impeding its freedom of
action, be padded with hemp, the more completely to exclude the air.
It was so contrived accordingly, by a proper arrangement of the cocks
and the machinery connected with them; that, while there was a vacuum
in one end of the cylinder, there should be an admission of steam
into the other; and the steam so admitted now served, not only by its
susceptibility of sudden condensation to create the vacuum, but also,
by its expansive force, to impel the piston.
These were the great improvements which Watt introduced in what may be
called the principle of the steam-engine, or, in other words, in the
manner of using and applying the steam. They constitute, therefore, the
grounds of his claim to be regarded as the true author of the conquest
that has been obtained by man over this powerful element. But original
and comprehensive as were the views out of which these fundamental
inventions arose, the exquisite and inexhaustible ingenuity which the
engine, as finally perfected by him, displays in every part of its
subordinate mechanism, is calculated to strike us perhaps with scarcely
less admiration. It forms undoubtedly the best exemplification that
has ever been afforded of the number and diversity of services which a
piece of machinery may be made to render to itself, by means solely of
the various application of its first moving power, when that has once
been called into action. Of these contrivances, however, we can only
notice one or two, by way of specimen. Perhaps the most singular is
that called the _governor_. This consists of an upright spindle, which
is kept constantly turning, by being connected with a certain part of
the machinery, and from which two balls are suspended, in opposite
directions, by rods, attached by joints, somewhat in the manner of
the legs of a pair of tongs. As long as the motion of the engine is
uniform, that of the spindle is so likewise, and the balls continue
steadily revolving at the same distance from each other. But as soon
as any alteration in the action of the piston takes place, the balls,
if it has become more rapid, fly further apart under the influence of
the increased centrifugal force which actuates them; or approach nearer
to each other in the opposite circumstances. This alone would have
served to indicate the state of matters to the eye; but Watt was not
to be so satisfied. He connected the rods with a valve in the tube by
which the steam is admitted to the cylinder from the boiler, in such a
way, that as they retreat from each other, they gradually narrow the
opening which is so guarded, or enlarge it as they tend to collapse;
thus diminishing the supply of steam when the engine is going too fast,
and when it is not going fast enough, enabling it to regain its proper
speed by allowing it an increase of aliment.
Again the constant supply of a sufficiency of water to the boiler is
secured by an equally simple provision, namely, by a _float_ resting on
the surface of the water which, as soon as it is carried down by the
consumption of the water to a certain point opens a valve and admits
more. And so on through all the different parts of the apparatus,
the various wonders of which cannot be better summed up than in the
forcible and graphic language of a recent writer:--“In the present
perfect state of the engine it appears a thing almost endowed with
intelligence. It regulates, with perfect accuracy and uniformity, the
_number of its strokes_ in a given time, _counting_, or _recording_
them moreover, to tell how much work it has done, as a clock records
the beats of its pendulum; it regulates the _quantity of steam_
admitted to work; the _briskness of the fire_; the _supply of water_
to the boiler; the _supply of coals_ to the fire; it _opens and shuts
its valves_ with absolute precision as to time and manner; it _oils
its joints_; it _takes out any air_ which may accidentally enter into
parts which should be vacuous; and when any thing goes wrong, which it
cannot of itself rectify, it _warns its attendants_ by ringing a bell;
yet, with all these talents and qualities, and even when exerting the
power of six hundred horses, it is obedient to the hand of a child;
its aliment is coal, wood, charcoal, or other combustible--it consumes
none when idle--it never tires, and wants no sleep; it is not subject
to malady when originally well made, and only refuses to work when worn
out with age; it is equally active in all climates, and will do work of
any kind; it is a water-pumper, a miner, a sailor, a cotton-spinner,
a weaver, a blacksmith, a miller, &c., &c.; and a small engine, in
the character of a _steam pony_, may be seen dragging after it on a
rail-road a hundred tons of merchandise, or a regiment of soldiers,
with greater speed than that of the fleetest coaches. It is the king of
machines, and a permanent realisation of the _Genii_ of Eastern fable,
whose supernatural powers were occasionally at the command of man.”