invention has given rise, one of the most mischievous in its
effects and most glaring in its falsehood, is the notion that
carriages thus propelled are more injurious to roads than
carriages drawn by horses. This error has been successfully
exposed in the evidence taken before the committee of the [Pg433]
House of Commons upon steam carriages. It is there demonstrated,
not only that carriages thus propelled do not wear a turnpike road
more rapidly than those drawn by horses, but that, on the other
hand, the wear by the feet of horses is far more rapid and
destructive than any which could be produced by the wheels of
carriages. Steam carriages admit of having the tires of the wheels
broad, so as to act upon the road more in the manner of rollers,
and thereby to give consistency and firmness to the material of
which the road is composed. The driving wheels being proved not to
slip upon the road, do not produce any effects more injurious than
the ordinary rolling wheels; consequently the wear occasioned by a
steam carriage upon a road, is not more than that produced by a
carriage drawn by horses, of an equivalent weight and the same or
equal tires; but the wear produced by the pounding and digging of
horses' feet in draught is many times greater than that produced
by the wear of any carriage. Those who still have doubts upon this
subject, if there be any such persons, will be fully satisfied by
referring to the evidence which accompanies the report of the
committee of the House of Commons, printed in October, 1831.
The weight of machinery necessary for steam carriages is sometimes
urged as an objection to their practical utility. Mr. Gurney
states, that, by successive improvements in the details of the
machinery, the weight of his carriages, without losing any of the
propelling power, may be reduced to 35 cwt., exclusive of the
load, and fuel and water: but thinks that it is possible to reduce
the weight still further.
A steam carriage constructed by Mr. Gurney, weighing 35 cwt.,
working for 8 hours, is found, according to his statement, to do
the work of about 30 horses. He calculates that the weight of his
propelling carriage, which would be capable of drawing 18 persons,
would be equal to the weight of 4 horses; and the carriage in
which these persons would be drawn would have the same weight as a
common stage coach capable of carrying the same number of persons.
Thus the weight of the whole—the propelling carriage and the
carriage for passengers taken together—would be the same [Pg434]
with the weight of a common stage coach, with 4 horses inclusive.
There are two methods of applying locomotives upon common roads to
the transport of passengers or goods; the one is by causing the
locomotive to carry, and the other to draw the load; and different
projectors have adopted the one and the other method. Each is
attended with its advantages and disadvantages. If the same
carriage transport the engine and the load, the weight of the
whole will be less in proportion to the load carried; also a
greater pressure may be produced on the wheels by which the load
is propelled. It is also thought that a greater facility in
turning and guiding the vehicle, greater safety in descending the
hills, and a saving in the original cost, will be obtained. On the
other hand, when the passengers are placed in the same carriage
with the engine, they are necessarily more exposed to the noise of
the machinery and to the heat of the boiler and furnace. The
danger of explosion is so slight, that, perhaps, it scarcely
deserves to be mentioned; but still _the apprehension_ of danger
on the part of the passengers, even though groundless, should not
be disregarded. This apprehension will be obviously removed or
diminished by transferring the passengers into a carriage separate
from the engine; but the greatest advantage of keeping the engine
separate from the passengers is the facility which it affords of
changing one engine for another in case of accident or derangement
on the road, in the same manner as horses are changed at the
different stages: or, if such an accident occur in a place where a
new engine cannot be procured, the load of passengers may be
carried forward by horses, until it is brought to some station
where a locomotive may be obtained. There is also an advantage
arising from the circumstance, that when the engines are under
repair, or in process of cleaning, the carriages for passengers
are not necessarily idle. Thus the same number of carriages for
passengers will not be required when the engine is used to draw as
when it is used to carry.
In case of a very powerful engine being used to carry great loads,
it would be quite impracticable to place the engine [Pg435] and
loads on four wheels, the pressure being such as no turnpike road
could bear. In this case it would be indispensably necessary to
place a part of the load at least upon separate carriages to be
drawn by the engine.
In the comparison of carriages propelled by steam with carriages
drawn by horses, there is no respect in which the advantage of the
former is so apparent as the safety afforded to the passenger.
Steam power is under the most perfect control, and a carriage thus
propelled is capable of being guided with the most admirable
precision. It is also capable of being stopped almost suddenly,
whatever be its speed: it is capable of being turned within a
space considerably less than that which would be necessary for
four-horse coaches. In turning sharp corners, there is no danger,
with the most ordinary care on the part of the conductor. On the
other hand, horse power, as is well known, is under very imperfect
control, especially when horses are used adapted to that speed
which at present is generally considered necessary for the
purposes of travelling. "The danger of being run away with and
overturned," says Mr. Farey, in his evidence before the House of
Commons, "is greatly diminished in a steam coach. It is very
difficult to control four such horses as can draw a heavy stage
coach ten miles an hour, in case they are frightened or choose to
run away; and, for such quick travelling, they must be kept in
that state of courage that they are always inclined to run away,
particularly down hill, and at sharp turns in the road. Steam
power has very little corresponding danger, being perfectly
controllable, and capable of having its power reversed, to retard
in going down hill. It must be carelessness that would occasion
the overturning of a steam carriage. The chance of breaking down
has been hitherto considerable, but it will not be more than in
stage coaches when the work is truly proportioned and properly
executed. The risk from explosion of the boiler is the only new
cause of danger, and that I consider not equivalent to the danger
from horses."
That the risk of accident from explosion is extremely slight, may
be proved by the fact that the railway between Liverpool and
Manchester has now been in operation for about ten [Pg436] years,
and that other railways more extensive in length have been worked
for a considerable time, and that no instance has ever yet
occurred of an accident to passengers from the explosion of a
boiler. Generally these machines, when they fail, are attended
with no other effect than the extinction of the fire, by the water
of the boiler flowing in upon it. I am not aware of more than one
instance, in which a serious accident has been produced by
explosion; and in that instance, the sufferers were only the
engineer and stoker. In the steam-engine of Mr. Gurney, the
carriage is drawn after the engine, as represented in _fig._ 117.
[Illustration: _Fig._ 117.]
[Illustration: _Fig._ 118.]
(206.) In the boiler to be used in the steam carriage projected by
Mr. Walter Hancock, the subdivision of the water is accomplished
by dividing a case or box by a number of [Pg437] thin plates of
metal, like a galvanic battery, the water being allowed to flow
between every alternate pair of plates, at E, _fig._ 118., and the
intermediate spaces H forming the flue through which the flame and
hot air are propelled.
In fact, a number of thin plates of water are exposed on both
sides to the most intense action of flame and heated air; so that
steam of a high pressure is produced in great abundance and with
considerable rapidity. The plates forming the boiler are bolted
together by strong iron ties, extending across the boiler, at
right angles to the plates, as represented in the figure. The
distance between the plates is two inches.
There are ten flat chambers of this kind for water, and
intermediately between them ten flues. Under the flues is the
fire-place, or grate, containing six square feet of fuel in vivid
combustion. The chambers are all filled to about two thirds of
their depth with water, and the other third is left for steam. The
water chambers, throughout the whole series, communicate with each
other both at top and bottom, and are held together by two large
bolts. By releasing these bolts, at any time, the chambers fall
asunder; and by screwing them up they may be all made tight again.
The water is supplied to the boiler by a forcing-pump, and the
steam issues from the centre of one of the flues at the top.
These boilers are constructed to bear a pressure of 400 or 500
lbs. on the square inch; but the average pressure of the steam on
the safety valve is from 60 to 100. There are 100 square feet of
surface in contact with the water exposed to the fire. The stages
which such an engine performs are eight miles, at the end of which
a fresh supply of fuel and water are taken in. It requires about
two bushels of coke for each stage.
The steam carriage of Mr. Hancock differs from that of Mr. Gurney
in this—that in the former the passengers and engine are all
placed on the same carriage. The boiler is placed behind the
carriage; and there is an engine-house between the boiler and the
passengers, the latter being placed in the fore part of the
vehicle; so that all the machinery is behind them. The carriages
are adapted to carry 14 [Pg438] passengers, and weigh, exclusive
of their load, about 3-1/2 tons, the tires of the wheels being
about 3-1/2 inches in breadth. Mr. Hancock states, that the
construction of his boiler is of such a nature, that, even in the
case of bursting, no danger is to be apprehended, nor any other
inconvenience than the stoppage of the carriage. He states that,
while travelling about nine miles an hour, and working with a
pressure of about 100 lbs. on the square inch, loaded with
thirteen passengers, the carriage was suddenly stopped. At first
the cause of the accident was not apparent; but, on opening one of
the cocks of the boiler, it was found that it contained neither
steam nor water. Further examination proved that the boiler had
burst. On unscrewing the bolts, it was found that there were
several large holes in the plates of the water-chamber, through
which the water had flowed on the fire, but neither noise nor
explosion, nor any dangerous consequences, ensued.
(207.) Mr. Nathaniel Ogle of Southampton obtained a patent for a
locomotive carriage, and worked it for some time experimentally;
but as his operations do not appear to have been continued, I
suppose he was unsuccessful in fulfilling those conditions,
without which the machine could not be worked with economy and
profit. In his evidence before a committee of the House of
Commons, he has thus described his contrivance:—
"The base of the boiler and the summit are composed of cross
pieces, cylindrical within and square without; there are holes
bored through these cross pieces, and inserted through the whole
is an air tube. The inner hole of the lower surface, and the under
hole of the upper surface, are rather larger than the other ones.
Round the air tube is placed a small cylinder, the collar of which
fits round the larger aperture on the inner surface of the lower
frame, and the under surface of the upper frame-work. These are
both drawn together by screws from the top; these cross pieces are
united by connecting pieces, the whole strongly bolted together;
so that we obtain, in one tenth of the space, and with one tenth
of the weight, the same heating surface and power as is now
obtained in other and low-pressure boilers, with incalculably
[Pg439] greater safety. Our present experimental boiler contains
250 superficial feet of heating surface in the space of 3 feet 8
inches high, 3 feet long, and 2 feet 4 inches broad, and weighs
about 8 cwt. We supply the two cylinders with steam, communicating
by their pistons with a crank axle, to the ends of which either
one or both wheels are affixed as may be required. One wheel is
found to be sufficient, except under very difficult circumstances,
and when the elevation is about one foot in six to impel the
vehicle forward.
"The cylinders of which the boiler is composed are so small as to
bear a greater pressure than could be produced by the quantity of
fire beneath the boiler; and if any one of these cylinders should
be injured by violence, or any other way, it would become merely a
safety valve to the rest. We never, with the greatest pressure,
burst, rent, or injured our boiler; and it has not once required
cleaning, after having been in use twelve months."
Dr. Church of Birmingham has obtained a succession of patents for
contrivances connected with a locomotive engine for stone roads;
and a company, consisting of a considerable number of individuals,
possessing sufficient capital, has been formed in Birmingham, for
carrying into effect his designs, and working carriages on his
principle. The present boiler of Dr. Church is formed of copper.
The water is contained between two sheets of copper, united
together by copper nails, in a manner resembling the way in which
the cloth forming the top of a mattress or cushion is united with
the cloth which forms the bottom of it, except that the nails or
pins, which bind the sheets of copper, are much closer together.
The water, in fact, seems to be "quilted" or "padded" in between
two sheets of thin copper. This double sheet of copper is formed
into an oblong rectangular box, the interior of which is the
fire-place and ash-pit, and over the end of which is the
steam-chest. The great extent of surface exposed to the immediate
action of the fire causes steam to be produced with great
rapidity.
Various other projects for the application of steam engines on
common roads were in a state of progressive improvement, [Pg440]
when the greater advantages attending railways were considered so
manifest, that considerable doubts were raised, whether, supposing
the problem of the application of the steam engine on common roads
to be successfully solved, it could ever be attended with the same
economy and effect, as by the adoption of a railway. Among the
projects which promised a successful issue, may be mentioned the
locomotive engines contrived by Messrs. Maudslay and Field, by
Colonel Maceroni, and by Mr. Scott Russell. These and others have,
however, been abandoned, mainly, we believe, from the impression,
that wherever traffic can exist, sufficiently extensive to render
the application of steam power profitable, a railway must always
supersede a common road; and that, even in the limited traffic to
be expected on branches to the great railways, horse power applied
to railways would be attended with more economy than steam power
applied on stone roads.
[Illustration]
[Pg441]
[Illustration]
CHAP. XIII.
STEAM NAVIGATION.
FORM AND ARRANGEMENT OF MARINE ENGINES. — EFFECTS OF SEA WATER
IN BOILERS. — REMEDIES FOR THEM. — BLOWING OUT. — INDICATORS
OF SALTNESS. — SEAWARD'S INDICATOR. — HIS METHOD OF BLOWING
OUT. — FIELD'S BRINE PUMPS. — TUBULAR CONDENSERS APPLIED BY
MR. WATT. — HALL'S CONDENSERS. — COPPER BOILERS. — PROCESS OF
STOKING. — MARINE BOILERS. — MEANS OF ECONOMISING FUEL. —
COATING MARINE BOILERS WITH FELT. — NUMBER AND ARRANGEMENT OF
FURNACES AND FLUES. — HOWARD'S ENGINE. — APPLICATION OF THE
EXPANSIVE PRINCIPLE IN MARINE ENGINES. — RECENT IMPROVEMENTS
OF MESSRS. MAUDSLAY AND FIELD. — HUMPHRYS' ENGINE. — COMMON
PADDLE-WHEEL. — FEATHERING PADDLES. — MORGAN'S WHEELS. — THE
SPLIT PADDLE. — PROPORTION OF POWER TO TONNAGE. — IMPROVED
EFFICIENCY OF MARINE ENGINES. — IRON STEAM-VESSELS. —
STEAM-NAVIGATION TO INDIA.
(208.) Among the many ways in which the steam-engine has
ministered to the advancement of civilisation and the social
progress of the human race, there is none more [Pg442] important
or more interesting than its application to navigation. Before it
lent its giant powers to the propulsion of ships, locomotion over
the waters of the deep was attended with so much danger and
uncertainty that, as a common proverb, it became the type and the
representative of every thing which was precarious and perilous.
The application, however, of steam to navigation has rescued the
mariner and the voyager from many of the dangers of wind and
water; and even in its present state, putting out of view its
probable improvement, it has rendered all voyages of moderate
length as safe, and very nearly as regular, as journeys over-land.
As a means of transport by sea, the application of this power may
be considered as established; and it is now receiving improvements
by which its extension to the longest class of ocean voyages is a
question not of practicability, but merely of profit.
The manner in which the steam-engine is rendered an instrument for
the propulsion of vessels must in its general features be so
familiar to every one as to require but short explanation. A shaft
is carried across the vessel, being continued on either side
beyond the timbers: to the extremities of this shaft, on the
outside of the vessel, are fixed a pair of wheels constructed like
undershot water-wheels, having attached to their rims a number of
flat boards called _paddle-boards_. As the wheels revolve, these
paddle-boards strike the water, driving it in a direction contrary
to that in which it is intended the vessel should be propelled.
The moving force imparted to the water thus driven backwards is
necessarily accompanied by a re-action upon the vessel through the
medium of the paddle-shaft, by which the vessel is propelled
forwards. On the paddle-shaft two cranks are constructed, similar
to the cranks already described on the axle of the driving wheels
of a locomotive engine. These cranks are placed at right angles to
each other, so that when either is in its highest or lowest
position the other shall be horizontal. They are driven by two
steam-engines, which are placed in the hull of the vessel below
the paddle-shaft. In the earlier steam-boats a single steam-engine
was used, and in that case the unequal action of the engine on the
crank was equalised by a fly-wheel. This, however, has been long
[Pg443] since abandoned in European vessels, and the use of two
engines is now almost universal. By the relative position of the
cranks it will be seen, that when either crank is at its dead
points, the other will be in the positions most favourable to its
action, and in all intermediate positions the relative efficiency
of the cranks will be such as to render their combined action very
nearly uniform.
The steam-engines used to impel vessels may be either condensing
engines, similar to those of Watt, and such as are used in
manufactures generally, or they may be non-condensing and
high-pressure engines, similar in principle to those used on
railways. Low-pressure condensing engines are, however, universally
used for marine purposes in Europe and to some extent in the United
States. In the latter country, however, high-pressure engines are
also in pretty general use, on rivers where lightness is a matter of
importance.
The arrangement of the parts of a marine engine differs in some
respects from that of a land engine. The limitation of space,
which is unavoidable in a vessel, renders greater compactness
necessary. The paddle-shaft on which the cranks to be driven by
the engine are constructed being very little below the deck of the
vessel, the beam and connecting rod could not be placed in the
position in which they usually are in land engines, without
carrying the machinery to a considerable elevation above the deck.
This is done in the steam-boat engines used on the American
rivers; but it would be inadmissible in steam-boats in general,
and more especially in sea-going steamers. The connecting rods,
therefore, instead of being presented downwards towards the cranks
which they drive, must, in steam-vessels, be presented upwards,
and the impelling force received from below. If, under these
circumstances, the beam were in the usual position above the
cylinder and piston-rod, it must necessarily be placed between the
engine and the paddle-shaft. This would require a depth for the
machinery which would be incompatible with the magnitude of the
vessel. The beam, therefore, of marine engines, instead of being
above the cylinder and piston, is placed below them. To the top of
the [Pg445] piston-rods cross pieces are attached of greater
length than the diameter of the cylinders, so that their
extremities shall project beyond the cylinders. To the ends of
these cross pieces are attached by joints the rods of a parallel
motion: these rods are carried downwards, and are connected with
the ends of two beams below the cylinder, and placed on either
side of it. The opposite ends of these beams are connected by
another cross piece, to which is attached a connecting rod, which
is continued upwards to the crank-pin, to which it is attached,
and which it drives. Thus the beam, parallel motion, and
connecting rod of a marine engine, is similar to that of a land
engine, only that it is turned upside down; and in consequence of
the impossibility of placing the beam directly over the
piston-rod, two beams and two systems of parallel motion are
provided, one on each side of the engine, acted upon by, and
acting on the piston-rod and crank by cross pieces.
The proportion of the cylinders differs from that usually observed
in land engines, for like reasons. The length of the cylinder of
land engines is generally greater than its diameter, in the
proportion of about two to one. The cylinders of marine engines
are, however, commonly constructed with a diameter very little
less than their length. In proportion, therefore, to their power
their stroke is shorter, which infers a corresponding shortness of
crank and a greater limitation of play of all the moving parts in
the vertical direction. The valves and the gearing by which they
are worked, the air-pump, the condenser, and other parts of the
marine engines, do not materially differ from those already
described in land engines.
[Illustration: _Fig._ 119.]
These arrangements of a marine engine will be more clearly
understood by reference to _fig._ 119.[35], in which is
represented a longitudinal section of a marine engine with its
boiler as placed in a steam-vessel. The sleepers of oak,
supporting the engine, are represented at X, the base of the
engine being secured to these by bolts passing through them
[Pg446] and the bottom timbers of the vessel; S is the steam-pipe
leading from the steam-chest in the boiler to the slides _c_, by
which it is admitted to the top and bottom of the cylinder. The
condenser is represented at B, and the air-pump at E. The hot well
is seen at F, from which the feed is taken for the boiler; L is
the piston-rod connected by the parallel motion _a_ with the beam
H, working on a centre K, near the base of the engine. The other
end of the beam I drives the connecting rod M, which extends
upwards to the crank which it works upon the paddle-shaft O. Q R
is the framing by which the engine is supported. The beam here
exhibited is shown on dotted lines as being on the further side of
the engine. A similar beam similarly placed, and moving on the
same axis, must be understood to be at this side connected with
the cross head of the piston in like manner by a parallel motion,
and with a cross piece attached to the lower end of the connecting
rod and to the opposite beam. The eccentric which works the slides
is placed upon the paddle shaft O, and the connecting arm which
drives the slides may be easily detached when the engine requires
to be stopped. The section of the boiler, grate, and flues, is
represented at W U. The safety-valve _y_ is enclosed beneath a
pipe carried up beside the chimney, and is inaccessible to the
engine-man; _h_ are the cocks for blowing the salted water from
the boiler; and I I the feed-pipe.
The general arrangement of the engine-room of a steam-vessel is
represented in _fig._ 120.