the dimensions of the vessel in which it is confined, or to the
force compressing it, is a quality which results immediately from
elasticity, and is consequently one which is peculiar to the gases
or elastic fluids, and does not at all appertain to liquids. If
the liquid contained in the vessel A B C D were transferred to a
vessel of twice the magnitude, it would only occupy half the
capacity of that vessel, and it could not by any means be
transferred, as we have supposed the air or gas to be, to a vessel
of half the dimensions, since it is inelastic and incompressible.
(13.) The elasticity of gases is likewise varied by varying the
temperature to which they are exposed; thus, in general, [Pg029]
if air or any other gas be augmented in temperature, it will
likewise be increased in elasticity; and if, on the other hand, it
be diminished in temperature, it will be likewise diminished in
its elastic force. The more heated, therefore, any air or gas
confined in a vessel becomes, the greater will be the force with
which it will press on the inner surface of that vessel, and tend
to burst it.
(14.) The same body may, by the agency of heat, be made to pass
successively through the different states of solid, liquid, and
gas, or vapour. The most familiar and obvious example of these
successive transitions is presented by water. Exposed to a certain
temperature, water can only exist as a solid; as the temperature
is increased, the ice, or solid water, is liquefied; and by the
continued application of heat, this water again undergoes a
change, and assumes the form, and acquires the mechanical
qualities, of air or gas: in such a state it is called STEAM.
This is a common property of all liquids. If they be exposed for a
sufficient length of time to a sufficient degree of heat, they
will always be converted into elastic fluids. These are usually
distinguished from air and other permanent gases, which never are
known to exist in the liquid form, by the term _vapour_, by which,
therefore, must be understood an elastic fluid which at common
temperatures exists in the liquid or solid state; by _steam_ is
expressed the vapour of water; and by _gases_, those elastic
fluids which like air are never known—at least, under ordinary
circumstances—to exist in any other but the elastic form.
(15.) When a liquid is caused, by the application of heat, to take
the form of an elastic fluid, or is evaporated, besides acquiring
the property of elasticity, it always undergoes a considerable
change of bulk. The amount of this change is different with
different liquids, and even with the same liquid it varies with
the circumstances under which the change is produced.
(16.) When water is evaporated under ordinary circumstances,—that
is, when exposed to no other external pressure than that of the
atmosphere,—it increases its volume about seventeen-hundred-fold.
Thus a cubic inch of liquid [Pg030] water would form about
seventeen hundred cubic inches of common steam. If, however, the
water be confined by a greater pressure than that produced by the
common atmosphere, then the increase of volume which takes place
in its evaporation would be less in proportion.
These important physical circumstances are now only indicated in a
general way. As we proceed with our account of the invention and
improvement of the steam engine, they will be developed more fully
and accurately.
(17.) After duly considering what has been just explained, no
difficulty will be found in comprehending the principles on which
the first rude attempts at the mechanical application of steam
already stated depend. In the apparatus ascribed to _Hero_ of
Alexandria, the elasticity of the vapour contained in the arms of
the revolving ball causes that vapour to issue from the lateral
orifices in the arms, such as that of G, _fig._ 1. As these
orifices, however, are exposed to the common atmosphere pressing
inwards with a force, the mean amount of which has been stated to
be about fifteen pounds per square inch, it follows that the steam
cannot escape from these orifices until its pressure or elasticity
exceeds this amount, and that when it does, the force with which
it will so escape will be the excess of its elasticity above that
of the atmosphere; and it is the reaction produced by this
difference of pressure, causing the arms to recoil, which will
give motion to the machine.
In the case of the apparatus of _De Caus_ (5.), the heat of the
fire acting on the vessel D C (_fig._ 2.) will raise the
temperature of the water contained in it, and also of the air
confined within it above the surface of that water. This air, as
it is increased in temperature, will also increase in elasticity;
it will therefore press on the surface of the water with increased
force, and will gradually force the water upwards in the tube; and
this effect would continue until all the water in the vessel would
be forced up the tube.
But at the same time that the heat acting on the vessel increases
the temperature of the air above the water, it also produces a
partial evaporation of the water, so that more or less steam is
mixed with the air in the vessel above the surface [Pg031] of the
water; and this steam possessing elasticity, unites with the air
in pressing on the surface of the water, and in raising it in the
tube.
[Illustration: _Figs._ 4, 5, and 6.]
Let us now revert to the brief account of the engine of the
Marquis of Worcester, described in "The Century of Inventions." We
collect from that description that the vessel in which the water
was evaporated was separate from those which contained the water
to be elevated; also that there were two vessels of the like
description, the contents of which were alternately elevated by
the pressure of the "water rarefied by the fire;" in other words
by steam; and that the water was raised in an uninterrupted
stream, by the management of two cocks communicating with these
vessels and with the boiler. The following is such an apparatus as
would answer this description. Let E (_fig._ 4.) be the vessel
containing the water to be evaporated, placed over a proper
furnace A; let S be a pipe to allow the steam produced from the
boiling water in E to pass into the vessels where its mechanical
action is required. Let R represent a cock or regulator, having in
it a curved passage, leading from S to the tube T, when the lever
or handle L is in the position represented by the cut; but leading
to the tube T′, when the lever L is turned one quarter of a
revolution to the right, as represented in _fig._ 5. By the
shifting of this lever, therefore, the steam pipe S may be made to
communicate alternately with the tubes T and T′. The tubes T and
T′ are carried respectively to two vessels V and V′, which are
filled with the water required to be raised. In these [Pg032]
vessels tubes enter at C and C′, descending nearly to the bottom:
these tubes have valves at B and B′, opening upwards, by which
water will be allowed to pass into the vertical tube F, but which
will not allow it to return downwards, the valves B and B′ being
then closed by the weight of the water above them.
Let G G′ be a pipe entering the sides of the vessels V and V′, for
the purpose of filling them with the water to be raised: let K be
a cock having a curved passage similar to the cock R, and leading
to a tube by which water is supplied from the reservoir or other
source from which the water to be raised is drawn. When the cock K
is placed as represented in _fig._ 4., the water from the
reservoir will flow through the curved passage in the cock K into
the tube G′, and thence into the vessel V′; but when this cock is
turned one quarter round, by shifting the lever to the left, it
will take the position represented in _fig._ 6., and the water
will flow through the curved passage into the tube G, and thence
into the vessel V. Let us now suppose the vessel V already filled
with water to be elevated, and the vessel V′ to have discharged
its contents. The cock R is turned, so as to allow the steam
generated in the boiler E to pass into the tube T, and thence into
the upper part of the vessel V, while the cock K is turned so as
to allow the water from the reservoir to pass into the tube G′,
and thence into the vessel V′. The steam collecting in the upper
part of the vessel V′ presses with its elastic force on the
surface of the water therein, and forces the water upwards in the
tube C; it passes through the valve B, which it opens by the
upward pressure received from the action of the steam, and thence
into the tube F, its descent into the tube C′ being prevented by
the valve V′, which can only be opened upwards. As the steam is
gradually supplied from the boiler E, the water in the vessel V is
forced up the tube C, through the valve B, and into the tube F,
until all the contents of the vessel V above the lower end of the
tube C have been raised. In the meanwhile, the vessel V′ has been
filled with water, through the cock K: when this has been
accomplished, the man who attends the machine shifts the cocks R
and K, so as to give them the position represented in _fig._ 5.
and _fig._ 6. [Pg033] In this position, the steam from the
boiler, being excluded from the tube T, will be conducted to the
tube T′, and thence to the vessel V′, while the water from the
reservoir will be excluded from the tube G′, and conducted through
the tube G to the vessel V. The vessel V will thus be replenished
and, by a process similar to that already described, the contents
of the vessel V′ will be forced up the tube C′, through the valve
B′, and into the tube F; its descent into the tube C being
prevented by the valve B, which will then be closed. After the
contents of the vessel V′ have thus been raised, and the vessel V
replenished, the two cocks R and K are once more shifted, and the
contents of V raised while V′ is replenished, and so on.
[Illustration: _Fig._ 4, 5, and 6.]
If, having comprehended the apparatus here described, the reader
refers to the description of the Marquis of Worcester's machine,
he will find that all the conditions therein laid down are
fulfilled by it. One vessel (E) of "water rarefied by fire" may by
such means "drive up forty (or more) of cold water; and the man
that tends the work has but to turn two cocks, that one vessel (V)
of water being consumed, another (V′) begins to force and refill
with cold water, and so on successively, the fire being tended and
kept constant; which the self-same person may likewise abundantly
perform, in the interim between the necessity of turning the said
cocks."
On comparing this with the contrivance previously suggested by De
Caus, it will be observed, that even if De Caus [Pg034] knew the
physical agent by which the water was driven upwards in the
apparatus described by him, still it was only a method of causing
a vessel of boiling water to empty itself; and before a repetition
of the process could be made, the vessel should be refilled, and
again boiled. In the contrivance of Lord Worcester, on the other
hand, the agency of the steam was employed in the same manner as
it is in the steam engines of the present day, being generated in
one vessel, and used for mechanical purposes in another. Nor must
this distinction be regarded as trifling or insignificant, because
on it depends the whole practicability of using steam as a
mechanical agent. Had its action been confined to the vessel in
which it was produced, it never could have been employed for any
useful purpose.
Although many of the projects contained in Lord Worcester's work
were in the highest degree extravagant and absurd, yet the engine
above described is far from being the only practicable and useful
invention proposed in it. On the contrary, many of his inventions
have been reproduced, and some brought into general use since his
time. Among these may be mentioned, stenography, telegraphs,
floating baths, speaking statues, carriages from which horses can
be disengaged if unruly, combination locks, secret escutcheons for
locks, candle moulds, the rasping mill, the gravel engine, &c.
SIR SAMUEL MORLAND, 1683.
(18.) Sir Samuel Morland was the son of a baronet of the same name,
who had received his title at the restoration for some services to
the royalist party, performed by him during the wars of the
Commonwealth. He appears to have devoted much attention to
mechanics, in which he attained some celebrity. He was the reputed
inventor of several ingenious contrivances, such as the drum capstan
for ships, the plunger pump, &c. He also investigated various
questions in acoustics, and among others, the determination of the
best form for the speaking-trumpet.
In 1680, Sir Samuel Morland was appointed Master [Pg035] of the
Works to Charles II., and in the following year was sent to
France, to execute some waterworks for Louis XIV. In 1683, while
in France, he wrote in the French language, a work entitled
"_Elevation des Eaux par toute sorte de Machines, reduite à la
Mesure, au Poids et à la Balance. Presentée à sa Majesté très
Chrestienne, par le Chevalier Morland, Gentilhomme Ordinaire de la
Chambre Privée, et Maistre des Méchaniques du Roi de la Grande
Brétagne, 1683._" This book is preserved in manuscript in the
Harleian Collection in the British Museum. It is written on
vellum, and consists of only thirty-eight pages. It contains
tables of measures and weights, theorems for the calculation of
the volumes of cylinders, the weights of columns of water, the
thickness of lead for pipes, and is concluded by a chapter on
steam, consisting of four pages, of which the following is a
translation:—
"_The principles of the new force of fire invented by Chevalier
Morland in 1682, and presented to His Most Christian Majesty in
1683_:—
"'Water being converted into vapour by the force of fire, these
vapours shortly require a greater space (about 2000 times) than the
water before occupied, and sooner than be constantly confined would
split a piece of cannon. But being duly regulated according to the
rules of statics, and by science reduced to measure, weight, and
balance, then they bear their load peaceably (like good horses), and
thus become of great use to mankind, particularly for raising water,
according to the following table, which shows the number of pounds
that may be raised 1800 times per hour to a height of six inches by
cylinders half filled with water, as well as the different diameters
and depths of the said cylinders.'"
There is nothing in the description here given which can indicate
the form of the machine by which Morland proposed to render the
force of steam a useful mover. It is, however, remarkable, that at
this early period, before experiments had been made on the
expansion which water undergoes in evaporation, he should have
given so near an approximation to [Pg036] the actual amount of
that expansion. It is scarcely supposable that such an estimate
could be obtained by him otherwise than by experiment.
The work containing the above description was not printed; but a
work bearing nearly the same title, containing, however, no
mention of the force of steam, was published by him in Paris in
the year 1685. In this he describes various experiments made by
him at St. Germains on the weight of the water of the Seine, and
gives weights of the columns of water, the contents of cylinders,
&c.
Soon after the publication of this work, Morland returned to
England, and resided near the court till his death. The celebrated
John Evelyn mentioned having paid a visit to him at his house at
Hammersmith, in 1695, when he had become aged and blind, but was
still remarkable for his mechanical ingenuity. "On the 25th of
October," says Evelyn, "the Archbishop and myself went to
Hammersmith to visit Sir Samuel Morland, who was entirely blind; a
very mortifying sight. He showed us his invention of writing
(short-hand), which was very ingenious; also his wooden kalendar,
which instructed him all by feeling; and other pretty and useful
inventions of mills, pumps, &c.; and the pump he had erected, that
serves water to his garden and to passengers, with an inscription,
and brings from a filthy part of the Thames near it a most perfect
and pure water."[3]
He died at Hammersmith, in January 1696; and before his death, as
a penance for his past life, was guilty of the eccentricity of
burying in the ground six feet deep a great collection of music
which he possessed.[4]
DENIS PAPIN, 1688.
(19.) Denis Papin, a native of Blois in France, and professor of
mathematics at Marbourg, is the name which stands next recorded in
the progressive invention of the steam engine. To this philosopher
is due the discovery of one of the qualities of steam, to the
proper management of which is owing much of the efficacy of the
modern steam engine. [Pg037]
Papin was born at Blois in France. He devoted his youth to the
study of medicine, in which he took a degree at Paris. The
revocation of the Edict of Nantes having driven him into exile, he
went to England, where the celebrated Boyle associated him in
several of his experiments with the air-pump, and caused him to be
elected a fellow of the Royal Society in 1681. Having been invited
to Germany by the Landgrave of Hesse, he discharged during several
years the duties of professor of mathematics at the university of
Marbourg, where he died in 1710. Notwithstanding his discoveries
respecting the agency of steam, he never received any mark of
distinction in his own country. The truth is, the importance and
value of these investigations were not apparent until long
afterwards.
This philosopher conceived the idea of producing a moving power by
means of a piston working in a cylinder, in the manner which we
shall now briefly explain.
[Illustration: _Fig._ 7.]
Let A B (_fig._ 7.) be a cylinder open at the top, and let a
piston P be fitted into it, so as to move in it air tight. At the
bottom of the cylinder suppose an opening provided, which can be
closed at pleasure, by a stop-cock, or otherwise, so that the
communication may be opened and closed at will between the
interior of the cylinder and the external air. This stop-cock
being opened, let the piston be drawn upwards till it reach the
top of the cylinder. Let the stop-cock at the bottom be then
removed, and imagine that some means can be supplied by which the
air within the cylinder can be suddenly annihilated. The piston,
now at the top, will have above it the pressure of the atmosphere;
and having no air below, it will be resisted in its descent by no
force save that arising from its friction with the cylinder. If,
then, the force of the air above the piston be greater than the
resistance arising from this friction, the piston will descend
with the excess of this force, and will continue so to descend
until it reach the bottom of the cylinder. Having attained that
position, let us [Pg038] suppose the stop-cock in the bottom
opened, so as to allow the external air to pass freely below the
piston. The piston may now be drawn to the top of the cylinder
again, offering no resistance save that of its weight, and its
friction with the cylinder. Having reached the top of the cylinder
once more, let the stop-cock be closed, and the air included
within the cylinder once more annihilated. A second descent of the
piston will take place, with the same force as before, and in like
manner the process may be continued indefinitely.
Now, if it should appear that means could be provided suddenly and
repeatedly to annihilate the air within the cylinder, and that the
pressure of the atmosphere above the piston should exert a force
compared with which the weight of the piston and its friction are
trifling, it is evident that a moving power would be obtained
which would be capable, by proper mechanism, of being applied to
any useful purpose, but which would more especially be applicable
to the working of pumps, the motion of which corresponds with that
which has been just ascribed to the piston in the cylinder. Such
were the first ideas of Papin. But in order to enable those who
are not conversant with physical science fully to appreciate their
importance, it will be necessary here to explain some of the
mechanical properties of atmospheric air.
(20.) The atmosphere is the thin, transparent, colourless, and
therefore invisible, fluid in which we live and move, which by
respiration sustains animal life, and is otherwise connected with
various important functions of organised matter. This fluid is so
light and attenuated, that it might at first be doubted whether it
be really a body at all; and, indeed, the name expressing
incorporeal beings, _spirit_, is a word in its origin signifying
_air_.[5] The air, however, is light only as compared with other
material substances, which exist in a more condensed state: it
possesses the quality of weight as absolutely as the most solid
and massive bodies in nature, and to render this quality manifest,
it is only necessary to submit a sufficient quantity of air to any
of the usual tests of gravitation. [Pg039]
A direct demonstration of this may be given by the following
experiment:—On the mouth of a flask let a stop-cock be fastened so
as to be air-tight. The interior of the flask may then be put into
free communication with the external air, or that communication may
be cut off at pleasure, by opening or closing the stop-cock. If a
syringe be applied to the mouth of the flask, the stop-cock being
open a part of the air contained in it may be drawn out. After this,
the stop-cock being closed, and the syringe detached, let the
flask be placed in the dish of a good balance, and accurately
counterpoised by weights in the other dish. This counterpoise will
then represent the weight of the flask, and of the air which has
remained in it. If the stop-cock be now opened, air will immediately
rush in, and replace that which the syringe had withdrawn from the
flask; and immediately the dish of the balance containing the flask
will sink by the effect of the weight of the air thus admitted into
the flask.
If the weight of quantity of air so small as to be capable of
being withdrawn by a syringe from an ordinary flask be thus of
sensible amount, it may be easily imagined that the vast mass of
atmosphere extending from the surface of the earth upwards, to a
height not ascertained with precision, but certainly not being
less than thirty miles, must be very considerable. Such a force,
pressing as it must constantly do, upon the surfaces of all
bodies, whether solid or fluid, and resisting and modifying their
movements, would play an important part in all mechanical
phenomena; and it is, therefore, not sufficient merely to have
recognised its existence, but it is most needful to measure its
amount with that degree of certainty and precision, which will
enable us to estimate its effects on those phenomena which we
shall have to investigate.
(21.) The amount of the pressure of the atmosphere on each square
inch of horizontal surface on which it rests, is obviously the
weight of the column of air extending from that square inch of
surface upwards to the top of the atmosphere. This force is
measured by the following means:—
[Illustration: _Fig._ 8.]
[Illustration: _Fig._ 9.]
Take a glass tube, A B (_fig._ 8.), above 32 inches long, open at
one end A, and closed at the other end B, and let it [Pg040] be
filled with mercury (quicksilver). Let a glass vessel or cistern
C, containing a quantity of mercury, be also provided. Applying
the finger at A, so as to prevent the mercury in the tube from
falling out, let the tube be inverted, and the end, stopped by the
finger, plunged into the mercury in C. When the end of the tube is
below the surface of the mercury in C (_fig._ 9.), let the finger
be removed. It will be found that the mercury in the tube will
not, as might be expected, fall to the level of the mercury in the
cistern C, which it would do were the end B open, so as to admit
the air into the upper part of the tube. On the other hand, the
level D of the mercury in the tube will be nearly 30 inches above
the level C of the mercury in the cistern.