(91.) The great object to be effected in the boilers of these engines

is, to keep a small quantity of water at an excessive temperature, by

means of a small quantity of fuel kept in the most active state of

combustion. To accomplish this, it is necessary, first, so to shape

the boiler, furnace, and flues, that the water shall be in contact

with as extensive a surface as possible, every part of which is acted

on either immediately, by the heat radiating from the fire, or

mediately, by the air which has passed through the fire, and which

finally rushes into the chimney: and, secondly, that such a forcible

draught should be maintained in the furnace, that a quantity of heat

shall be extricated from the fuel, by combustion, sufficient to

maintain the water at the necessary temperature, and to produce the

steam with sufficient rapidity. To accomplish these objects,

therefore, the chamber containing the grate should be completely

surrounded by water, and should be below the level of the water in the

boiler. The magnitude of the surface exposed to radiation should be as

great as is consistent with the whole magnitude of the machine. The

comparative advantage which the Rocket possessed in these respects

over the other engines will be evident on inspection. In the next

place, it is necessary that the heat, which is absorbed by the air

passing through the fuel, and keeping it in a state of combustion,

should be transferred to the water before the air escapes into the

chimney. Air being a bad conductor of heat, to accomplish this it is

necessary that the air in the flues should be exposed to as great an

extent of surface in contact with the water as possible. No

contrivance can be less adapted for the attainment of this end than

one or two large tubes traversing the boiler, as in the earliest

locomotive engines: the body of air which passes through the centre of

these tubes had no contact with their surface, and, consequently,

passed into the chimney at nearly the same temperature as that which

it had when it quitted the fire. The only portion of air which

imparted its heat to the water was that portion which passed next to

the surface of the tube.

Several methods suggest themselves to increase the surface of water in

contact with a given quantity of air passing through it. This would be

accomplished by causing the air to pass between plates placed near

each other, so as to divide the current into thin strata, having

between them strata of water, or it might be made to pass between

tubes differing slightly in diameter, the water passing through an

inner tube, and being also in contact with the external surface of the

outer tube. Such a method would be similar in principle to the

steam-jacket used in _Watt's_ steam engines, or to the condenser of

_Cartwright's_ engine already described. But, considering the facility

of constructing small tubes, and of placing them in the boiler, that

method, perhaps, is, on the whole, the best in practice; although the

shape of a tube, geometrically considered, is most unfavourable for

the exposure of a fluid contained in it to its surface. The air which

passes from the fire-chamber, being subdivided as it passes through

the boiler by a great number of very small tubes, may be made to

impart all its excess of heat to the water before it issues into the

chimney. This is all which the most refined contrivance can effect.

The Rocket engine was traversed by 25 tubes, each 3 inches in

diameter; and the principle has since been carried to a much greater

extent.

The abstraction of a great quantity of heat from the air before it

reaches the chimney is attended with one consequence, which, at first

view, would present a difficulty apparently insurmountable; the

chimney would, in fact, lose its power of draught. This difficulty,

however, was removed by using the waste steam, which had passed from

the cylinder after working the engine, for the purpose of producing a

draught. This steam was urged through a jet presented upwards in the

chimney, and driven out with such force in that direction as to create

a sufficient draught to work the furnace.

It will be observed that the principle of draught in the Novelty is

totally distinct from this: in that engine the draught is produced by

a bellows worked by the engine. The question, as far as relates to

these two methods, is, whether more power is lost in supplying the

steam through the jet, as in the Rocket, or in working the bellows, as

in the Novelty. The force requisite to impel the steam through the jet

must be exerted by the returning stroke of the piston, and,

consequently, must rob the working effect to an equivalent amount. On

the other hand, the power requisite to work the bellows in the Novelty

must be subducted from the available power of the engine. The former

method is found to be the more effectual and economical.

The importance of these details will be understood, when it is

considered that the only limit to the attainment of speed by

locomotive engines is the power to produce in a given time a certain

quantity of steam. Each stroke of the piston causes one revolution of

the wheels, and consumes two cylinders full of steam: consequently, a

cylinder of steam corresponds to a certain number of feet of road

travelled over: hence it is that the production of a rapid and

abundant supply of heat, and the imparting of that heat quickly and

effectually to the water, is the key to the solution of the problem to

construct an engine capable of rapid motion.

The method of subdividing the flue into tubes was carried much further

by Mr. _Stephenson_ after the construction of the Rocket; and, indeed,

the principle was so very obvious, that it is only surprising that, in

the first instance, tubes of smaller diameter than 3 inches were not

used. In engines since constructed, the number of tubes vary from 90

to 120, the diameter being reduced to 2 inches or less, and in some

instances tubes have been introduced, even to the number of 150, of

1-1/2 inch diameter. In the Meteor, 20 square feet are exposed to

radiation, and 139 to the contact of heated air; in the Arrow, 20

square feet to radiation, and 145 to the contact of heated air. The

superior economy of fuel gained by this means will be apparent by

inspecting the following table, which exhibits the consumption of fuel

which was requisite to convey a ton weight a mile in each of four

engines, expressing also the rate of the motion:--

+------------------+---------------+-----------------+

| |Average rate of|Consumption of |

| Engines. | speed in miles|Coke in pounds |

| | per hour. |per ton per mile.|

+------------------+---------------+-----------------+

|No. 1. Rocket | 14 | 2·41 |

| 2. Sanspareil | 15 | 2·47 |

| 3. Phoenix | 12 | 1·42 |

| 4. Arrow | 12 | 1·25 |

+------------------+---------------+-----------------+

(92.) Since the period at which the railway was opened for the actual

purposes of transport, the locomotive engines have been in a state of

progressive improvement. Scarcely a month has passed without

suggesting some change in the details, by which fuel might be

economised, the production of steam rendered more rapid, the wear of

the engine rendered slower, the proportionate strength of the

different parts improved, or some other desirable end obtained. The

consequence of this has been, that the particular engines to which we

have alluded, and others of the same class, without having, as it

were, lived their natural life, or without having been worn out by

work, have been laid aside to give place to others of improved powers.

By the exposure of the cylinders to the atmosphere in the Rocket, and

engines of a similar form, a great waste of heat was incurred, and it

was accordingly determined to remove them from the exterior of the

boiler, and to place them within a casing immediately under the

chimney: this chamber was necessarily kept warm by its proximity to

the end of the boiler, but more by the current of heated air which

constantly rushed into it from the tubes. This change, also, rendered

necessary another, which improved the working of the engine. In the

earlier engines the motion of the piston was communicated to the wheel

by a connecting rod attached to one of the spokes on the exterior of

the wheel, as represented in fig. 55. By the change to which we have

just alluded, the cylinders being placed between the wheels under the

chimney, this mode of working became inapplicable, and it was

considered better to connect the piston-rods with two cranks placed at

right angles on the axles of the great wheels. By this means, it was

found that the working of the machine was more even, and productive of

less strain than in the former arrangement. On the other hand, a

serious disadvantage was incurred by the adoption of a cranked axle.

The weakness necessarily arising from such a form of axle could only

be counterbalanced by great thickness and weight of metal; and even

this precaution does not prevent the occasional fracture of such axles

at the angles of the cranks. The advantages, however, of this plan, on

the whole, are considered to predominate.

In the most improved engines in present use two safety-valves are

provided, of which only one is in the power of the engine-man. The

tubes being smaller and more numerous than in the earlier engines, the

heat is more completely extracted from the air before it enters the

chimney. A powerful draft is rendered still more necessary by the

smallness of the tubes: this is effected by forcing the steam which

has worked the pistons through a contracted orifice, presented upwards

in the chimney, by the regulation of which any degree of draft may be

obtained.

One of the most improved engines at present in use is represented in

fig. 61.

A represents the cylindrical boiler, the lower half of which is

traversed by tubes, as described in the Rocket. They are usually from

80 to 100 in number, and about 1-1/2 inch in diameter; the boiler is

about 7 feet in length; the fire-chamber is attached to one end of it,

at F, as in the Rocket, and similar in construction; the cylinders are

inserted in a chamber at the other end, immediately under the chimney.

The piston-rods are supported in the horizontal position by guides;

and connecting rods extend from them, under the engine, to the two

cranks placed on the axle of the large wheels. The effects of any

inequality in the road are counteracted by springs, on which the

engine rests; the springs being below the axle of the great wheels,

and above that of the less. The steam is supplied to the cylinders,

and withdrawn, by means of the common sliding valves, which are worked

by an eccentric wheel placed on the axle of the large wheels of the

carriage. The motion is communicated from this eccentric wheel to the

valve by sliding rods. The stand is placed for the attendant at the

end of the engine, next the fire-place, F; and two levers, L, project

from the end, which communicate with the valves by means of rods, by

which the engine is governed, so as to stop or reverse the motion.

[Illustration: _Fig. 61._]

The wheels of these engines have been commonly constructed of wood,

with strong iron tires, furnished with flanges adapted to the rails.

But Mr. _Stephenson_ has recently substituted, in some instances,

wheels of iron with hollow spokes. The engine draws after it a tender

carriage containing the fuel and water; and, when carrying a light

load, is capable of performing the whole journey from Liverpool to

Manchester without a fresh supply of water. When a heavy load of

merchandise is drawn, it is usual to take in water at the middle of

the trip.

(93.) In reviewing all that has been stated, it will be perceived that

the efficiency of the locomotive engines used on this railway is

mainly owing to three circumstances: 1st, The unlimited power of draft

in the furnace, by projecting the waste steam into the chimney; 2d,

The unlimited abstraction of heat from the air passing from the

furnace, by Mr. _Booth's_ ingenious arrangement of tubes traversing

the boiler; and, 3d, Keeping the cylinders warm, by immersing them in

the chamber under the chimney.[27] There are many minor details which

might be noticed with approbation, but these constitute the main

features of the improvements, and should never, for a moment, be lost

sight of by projectors of locomotive engines.

[Footnote 27: Mr. Robert Stephenson, whose experience and skill in the

construction of locomotives attaches great importance to this

condition. It has lately, however, been abandoned by some other

engine-makers, for the purpose of getting rid of the cranked axle

which must accompany it.]

The successive introduction of improvements in the engines, some of

which we have mentioned, has been accompanied by corresponding

accessions to their practical power, and to the economy of fuel; and

they have now arrived at a point which is as far beyond the former

expectations of the most sanguine locomotive projectors, as it

assuredly is short of the perfection of which these wonderful machines

are still susceptible.

In the spring of the year 1832, I made several experiments on the

Manchester railway, with a view to determine, in the actual state of

the locomotive engines at that time, their powers with respect to the

amount of load and the economy of fuel. Since that time I am not aware

that, in these respects, the engine has received any material

improvement. The following are the particulars of three experiments

thus made:--

I.

On Saturday, the 5th of May, the engine called the "Victory" took 20

wagons of merchandise, weighing gross 92 tons 19 cwt. 1 qr., together

with the tender containing fuel and water, of the weight of which I

have no account, from Liverpool to Manchester (30 miles,) in 1 h. 34

min. 45 sec. The train stopped to take in water half-way, for 10

minutes, not included in the above mentioned time. On the inclined

plane rising 1 in 96, and extending 1-1/2 mile, the engine was

assisted by another engine called the "Samson," and the ascent was

performed in 9 minutes. At starting, the fire-place was well filled

with coke, and the coke supplied to the tender accurately weighed. On

arriving at Manchester the fire-place was again filled, and the coke

remaining in the tender weighed. The consumption was found to amount

to 929 pounds net weight, being at the rate of one third of a pound

per ton per mile.

Speed on the level was 18 miles an hour; on a fall of 4 feet in a

mile, 21-1/2 miles an hour; fall of 6 feet in a mile, 25-1/2 miles an

hour; on the rise over Chatmoss, 8 feet in a mile 17-5/8 miles an

hour; on level ground sheltered from the wind, 20 miles an hour. The

wind was moderate, but direct ahead. The working wheels slipped three

times on Chatmoss, and the train was retarded from 2 to 3 minutes.

The engine, on this occasion, was not examined before or after the

journey, but was presumed to be in good working order.

II.

On Tuesday, the 8th of May, the same engine performed the same

journey, with 20 wagons, weighing gross 90 tons 7 cwt. 2 qrs.,

exclusive of the unascertained weight of the tender. The time of the

journey was 1 h. 41 min. The consumption of coke 1040 lbs. net weight,

estimated as before. Rate of speed:--

Level 17-5/8 miles per hour.

Fall of 4 feet in a mile 22

---- 6 22-1/2

Rise of 8 15

On this occasion there was a high wind ahead on the quarter, and the

connecting rod worked hot, owing to having been keyed too tight. On

arriving at Manchester, I caused the cylinders to be opened, and found

that the pistons were so loose, that the steam blew through the

cylinders with great violence. By this cause, therefore, the machine

was robbed of a part of its power during the journey; and this

circumstance may explain the slight decrease in speed, and increase in

the consumption of fuel, with a lighter load in this journey compared

with that performed on the 5th of May.

The Victory weighs 8 tons 2 cwt., of which 5 tons 4 cwt. rest on the

drawing wheels. The cylinders are 11 inches diameter, and 16 inches

stroke; and the diameter of the drawing wheels is 5 feet.

III.

On the 29th of May, the engine called the "Samson," (weighing 10 tons

2 cwt., with 14-inch cylinders, and 16-inch stroke; wheels 4 feet 6

inches diameter, both pairs being worked by the engine; steam 50 lbs.

pressure, 130 tubes) was attached to 50 wagons, laden with

merchandise; net weight about 150 tons; gross weight, including

wagons, tender, &c., 223 tons 6 cwt. The engine with this load

travelled from Liverpool to Manchester (30 miles) in 2 h. and 40 min.,

exclusive of delays upon the road for watering, &c., being at the

rate of nearly 12 miles an hour. The speed varied according to the

inclinations of the road. Upon a level, it was 12 miles an hour; upon

a descent of 6 feet in a mile, it was 16 miles an hour: upon a rise of

8 feet in a mile, it was about 9 miles an hour. The weather was calm,

the rails very wet; but the wheels did not slip, even in the slowest

speed, except at starting, the rails being at that place soiled and

greasy with the slime and dirt to which they are always exposed at the

stations. The coke consumed in this journey, exclusive of what was

raised in getting up the steam, was 1762 lbs., being at the rate of a

quarter of a pound per ton per mile.

(94.) From the above experiments it appears that a locomotive engine,

in good working order, with its full complement of load, is capable of

transporting weights at an expense in fuel amounting to about 4 ounces

of coke per ton per mile. The attendance required on the journey is

that of an engine-man and a fire-boy; the former being paid 1_s._

6_d._ for each trip of 30 miles, and the latter 1_s._ In practice,

however, we are to consider, that it rarely happens that the full

complement of load can be sent with the engines; and when lesser loads

are transported, the _proportionate expense_ must for obvious reasons,

be greater.

The practical expenditure of fuel on the Liverpool and Manchester line

may, perhaps, be fairly estimated at half a pound of coke per ton per

mile.

(95.) Having explained the power and efficiency of these locomotive

engines, it is now right to notice some of the defects under which

they labour.

The great original cost, and the heavy expense of keeping the engines

used on the railway in repair, have pressed severely on the resources

of the undertaking. One of the best constructed of the later engines

costs originally about 800_l._ It may be hoped that, by the excitement

of competition, the facilities derived from practice, and from the

manufacture of a greater number of engines of the same kind, some

reduction of this cost may be effected. The original cost, however, is

far from being the principal source of expense: the wear and tear of

these machines, and the occasional fracture of those parts on which

the greatest strain has been laid, have greatly exceeded what the

directors had anticipated. Although this source of expense must be in

part attributed to the engines not having yet attained that state of

perfection, in the proportion and adjustment of their parts, of which

they are susceptible, and to which experience alone can lead, yet

there are some obvious defects which demand attention.

The heads of the boilers are flat, and formed of iron, similar to the

material of the boilers themselves. The tubes which traverse the

boiler were, until recently, copper, and so inserted into the flat

head or ends as to be water-tight. When the boiler is heated, the

tubes are found to expand in a greater degree than the other parts of

the boiler; which frequently causes them either to be loosened at the

extremities, so as to cause leakage, or to bend from want of room for

expansion. The necessity of removing and refastening the tubes causes,

therefore, a constant expense.

It will be recollected that the fire-place is situated at one end of

the boiler, immediately below the mouths of the tubes: a powerful

draught of air, passing through the fire, carries with it ashes and

cinders, which are driven violently through the tubes, and especially

the lower ones, situated near the fuel. These tubes are, by this

means, subject to rapid wear, the cinders continually acting upon

their interior surface. After a short time it becomes necessary to

replace single tubes, according as they are found to be worn, by new

ones; and it not unfrequently happens, when this is neglected, that

tubes burst. After a certain length of time the engines require new

tubing, which is done at the expense of about 70_l._, allowing for the

value of the old tubes. This wear of the tubes might possibly be

avoided by constructing the fire-place in a lower position, so as to

be more removed from their mouths; or, still more effectually, by

interposing a casing of metal, which might be filled with water,

between the fire-place and those tubes which are the most exposed to

the cinders and ashes. The unequal expansion of the tubes and boilers

appears to be an incurable defect, if the present form of the engine

be retained. If the fire-place and chimney could be placed at the same

end of the boiler, so that the tubes might be recurved, the unequal

expansion would then produce no injurious effect; but it would be

difficult to clean the tubes if they were exposed, as they are at

present, to the cinders. The next source of expense arises from the

wear of the boiler-head, which is exposed to the action of the fire.

These require constant patching and frequent renewal.

A considerable improvement has lately been introduced into the method

of tubing, by substituting brass for copper tubes. We are not aware

that the cause of this improvement has been discovered; but it is

certain, whatever be the cause, that brass tubes are subject to

considerably slower wear than copper.

It has been said by some whose opinions are adverse to the advantage

of railways, but more especially to the particular species of

locomotive engines now under consideration, that the repairs of one of

these engines cost so great a sum as 1500_l._ per annum, and that the

directors now think of abandoning them, or adopting either stationary

engines or horse-power. As to the first of these statements I must

observe, that the expense of repairs of such machines should never be

computed in reference to _time_, but rather to the work done, or the

distance travelled over. I have ascertained that engines frequently

travel a distance of from 25,000 to 30,000 miles before they require

new tubing. During that work, however, single tubes are, of course,

occasionally renewed, and other repairs are made, the expense of which

may safely be stated as under the original cost of the engine. The

second statement, that the company contemplate substituting stationary

engines, or horses, for locomotives, is altogether at variance with

the truth. Whatever improvements may be contemplated in locomotives,

the directors assuredly have not the slightest intention of going back

in the progress of improvement, in the manner just mentioned.

The expense of locomotive power having so far exceeded what was

anticipated at the commencement of the undertaking, it was thought

advisable, about the beginning of the year 1834, to institute an

inquiry into the causes which produced the discrepancy between the

estimated and actual expenses, with a view to the discovery of some

practical means by which they could be reduced. The directors of the

company, for this purpose, appointed a sub-committee of their own

body, assisted by Mr. _Booth_, their treasurer, to inquire and report

respecting the causes of the amount of this item of their expenditure,

and to ascertain whether any and what measures could be devised for

the attainment of greater economy. A very able and satisfactory report

was made by this committee, or, to speak more correctly by Mr.

_Booth_.

It appears that, previous to the establishment of the railway, Messrs.

_Walker_ and _Rastrick_, engineers, were employed by the company to

visit various places where steam power was applied on railways, for

the purpose of forming an estimate of the probable expense of working

the railway by locomotive and by fixed power. These engineers

recommended the adoption of locomotive power, and their estimate was,

that the transport might be effected at the rate of .278 of a penny,

or very little more than a farthing per ton per mile. In the year

1833, five years after this investigation took place, it was found

that the actual cost was .625 of a penny, or something more than a

halfpenny per ton per mile, being considerably above double the

estimated rate. Mr. _Booth_ very properly directed his inquiries to

ascertain the cause of this discrepancy, by comparing the various

circumstances assumed by Messrs. _Walker_ and _Rastrick_, in making

their estimate, with those under which the transport was actually

effected. The first point of difference which he observed was the

speed of transport: the estimate was founded on an assumed _speed_ of

ten miles an hour, and it was stated that a fourfold speed would

require an addition of 50 per cent. to the power, without taking into

account wear and tear. Now the actual speed of transport being double

the speed assumed in the statement, Mr. _Booth_ holds it to be

necessary to add 25 per cent. on that score.

The next point of difference is in the amount of the loads: the

estimate is founded upon the assumption, that every engine shall start

with its full complement of load, and that with this it shall go the

whole distance. "The facts, however, are," says Mr. _Booth_, "that,

instead of a _full load_ of profitable carriage _from_ Manchester,

about half the wagons _come back empty_, and, instead of the tonnage

being conveyed the whole way, many thousand tons are conveyed only

half the way; also, instead of the daily work being uniform, it is

extremely fluctuating." It is further remarked, that in order to

accomplish the transport of goods from the branches and from

intermediate places, engines are despatched several times a day, from

both ends of the line, _to clear the road_; the object of this

arrangement being rather to lay the foundation of a beneficial

intercourse in future, than with a view to any immediate profit. Mr.

_Booth_ makes a rough estimate of the disadvantages arising from these

circumstances by stating them at 33 per cent. in addition to the

original estimate.

The next point of difference is the fuel. In the original estimate

_coal_ is assumed as the fuel, and it is taken at the price of five

shillings and tenpence per ton: now the act of parliament forbids the

use of coal which would produce smoke; the company have, therefore,

been obliged to use _coke_, at seventeen shillings and sixpence a

ton. Taking coke, then, to be equivalent to coal, ton for ton, this

would add .162 to the original estimate.

These several discrepancies being allowed for, and a proportional

amount being added to the original estimate, the amount would be

raised to .601 of a penny per ton per mile, which is within one

fortieth of a penny of the actual cost. This difference is considered

to be sufficiently accounted for by the wear and tear produced by the

very rapid motion, more especially when it is considered that many of

the engines were constructed before the engineer was aware of the

great speed that would be required.

"What then," says Mr. _Booth_, in the Report already alluded to, "is

the result of these opposite and mutually counteracting circumstances?

and what is the present position of the company in respect of their

moving power? Simply, that they are still in a course of experiment,

to ascertain practically the best construction, and the most durable

materials, for engines required to transport greater weights, and at

greater velocities, than had, till very recently, been considered

possible; and which, a few years ago, it had not entered into the

imagination of the most daring and sanguine inventor to conceive: and,

farther, that these experiments have necessarily been made, not with

the calm deliberation and quiet pace which a salutary caution

recommends,--making good each step in the progress of discovery before

advancing another stage,--but amidst the bustle and responsibilities

of a large and increasing traffic; the directors being altogether

ignorant of the time each engine would last before it would be laid up

as inefficient, but compelled to have engines, whether good or bad;

being aware of various defects and imperfections, which it was

impossible at the time to remedy, yet obliged to keep the machines in

motion, under all the disadvantages of heavy repairs, constantly going

on during the night, in order that the requisite number of engines

might be ready for the morning's work. Neither is this great

experiment yet complete; it is still going forward. But the most

prominent difficulties have been in a great measure surmounted, and

your committee conceive, that they are warranted in expecting, that

the expenditure in this department will, ere long, be materially

reduced, more especially when they consider the relative performances

of the engines at the _present time_ compared with what it was two

years ago."

In the half year ending 31st December, 1831, the six best engines

performed as follows:--

Miles.

Planet 9,986

Mercury 11,040

Jupiter 11,618

Saturn 11,786

Venus 12,850

Etna 8,764

------

Making in all 66,044

------

In the half year ending 31st December, 1833, the six best engines

performed as follows:--

Miles.

Jupiter 16,572

Saturn 18,678

Sun 15,552

Etna 17,763

Ajax 11,678

Firefly 15,608

------

Making in all 95,851

------

(96.) The advantages derivable from railroads are greatly abridged by

the difficulty arising from those changes of level to which all roads

are necessarily liable; but in the case of railroads, from causes

peculiar to themselves, these changes of level occasion great

inconvenience. To explain the nature of these difficulties, it will be

necessary to consider the relative proportion which must subsist

between the power of traction on a level and on an inclined plane. On

a level railroad the force of traction necessary to propel any load,

placed on wheel carriages of the construction now commonly used, may

perhaps be estimated at 7-1/2 pounds,[28] for every ton gross in the

load; that is to say, if a load of one ton gross were placed upon

wheel carriages upon a level railroad, the traces of horses drawing it

would be stretched with a force equivalent to 7-1/2 pounds. If the

load amounted to two or three tons, the tension of the traces would be

increased to 15 or 22-1/2 pounds, and so on. The necessity of this

force of traction, arising from the want of perfect smoothness in the

road, and from the friction of the wheels and axles of the carriages,

must be the same whether the road be level or inclined; and

consequently, in ascending an inclined plane, the same force of

traction will be necessary in addition to that which arises from the

tendency of the load to fall down the plane. This latter tendency is

always in the proportion of the elevation of the plane to its length;

that is to say, a plane which rises 1 foot in 100 will give a weight

of 100 tons a tendency to fall down the plane amounting to 1 ton, and

would therefore add 1 ton to the force of traction necessary for such

a load on a level.

[Footnote 28: The estimate commonly adopted by engineers at present is

9 pounds per ton. I have no doubt, however, that this is too high. I

am now (November, 1835,) engaged in an extensive course of experiments

on different railways, with a view to determine with precision this

and other points connected with the full developement of their theory;

and I have reason to believe, from the observations I have already

made, that even 7-1/2 pounds per ton is above the average force of

traction upon the level.]

Now since 7-1/2 pounds is very nearly the 300th part of a ton, it

follows that if an inclination upon a railroad rises at the rate of 1

foot in 300, or, what is the same, 17-1/2 feet in a mile, such an

acclivity will add 7-1/2 pounds per ton to the force of traction. This

acclivity therefore would require a force of traction twice as great

as a level. In like manner a rise of 35 feet in a mile would require

three times the force of traction of a level, 52-1/2 feet in a mile

four times that force, and so on. In fact, for every 7 feet in a mile

which an acclivity rises, 3 pounds per ton will be added to the force

of traction. If we would then ascertain the power necessary to pull a

load up any given acclivity upon a railroad, we must first take 7-1/2

pounds as the force necessary to overcome the common resistance of the

road, and then add 3 pounds for every 7 feet which the acclivity rises

per mile. For example, suppose an acclivity to rise at the rate of 70

feet in a mile, the force of traction necessary to draw a ton up it

would be thus calculated:--

Friction 7-1/2 lbs.

70 feet = 10 times 3 lbs. 30

------

Total force 37-1/2

It will be apparent, therefore, that if a railroad undulates by

inclined planes, even of the most moderate inclinations, the

propelling power to be used upon it must be of such a nature as to be

capable of increasing its intensity in a great degree, according to

the elevation of the planes which it has to encounter. A plane which

rises 52-1/2 feet per mile presents to the eye scarcely the appearance

of an ascent, and yet requires the power of traction to be increased

in a fourfold proportion.

It is the property of animal power, that within certain limits its

energy can be put forth at will, according to the exigency of the

occasion; but the intensity of mechanical power, in the instance now

considered, cannot so conveniently be varied, except indeed within

narrow limits.

In the application of locomotive engines upon railways the difficulty

arising from inclined planes has been attempted to be surmounted by

several methods, which we shall now explain.

1. Upon arriving at the foot of the plane the load is divided, and the

engine carries it up in several successive trips, descending the

plane unloaded after each trip. The objection to this method is the

delay which it occasions,--a circumstance which is incompatible with a

large transport of passengers. From what has been stated, it would be

necessary, when the engine is fully loaded on a level, to divide its

load into four parts, to be successively carried up when the incline

rises 52 feet per mile. This method has been practised in the

transport of merchandise occasionally, when heavy loads were carried

on the Liverpool and Manchester line, upon the Rainhill incline.

2. A subsidiary or assistant locomotive engine may be kept in constant

readiness at the foot of each incline, for the purpose of aiding the

different trains, as they arrive, in ascending. The objection to this

mode is the cost of keeping such an engine with its boiler continually

prepared, and its steam up. It would be necessary to keep its fire

continually lighted, whether employed or not; otherwise, when the

train would arrive at the foot of the incline, it should wait until

the subsidiary engine was prepared for work. In cases where trains

would start and arrive at stated times, this objection, however, would

have less force. This method is at present generally adopted on the

Liverpool and Manchester line. This method, however, cannot be

profitably applied to planes of any considerable length.

3. A fixed steam engine may be erected on the crest of the incline, so

as to communicate by ropes with the train at the foot. Such an engine

would be capable of drawing up one or two trains together, with their

locomotives, according as they would arrive, and no delay need be

occasioned. This method requires that the fixed engine should be kept

constantly prepared for work, and the steam continually up in the

boiler. This expedient is scarcely compatible with a large transit of

passengers, except at the terminus of a line.

4. In working on the level, the communication between the boiler and

the cylinder in the locomotives may be so restrained by partially

closing the throttle valve, as to cause the pressure upon the piston

to be less in a considerable degree than the pressure of steam in the

boiler. If under such circumstances a sufficient pressure upon the

piston can be obtained to draw the load on the level, the throttle

valve may be opened on approaching the inclined plane, so as to throw

on the piston a pressure increased in the same proportion as the

previous pressure in the boiler was greater than that upon the piston.

If the fire be sufficiently active to keep up the supply of steam in

this manner during the ascent, and if the rise be not greater in

proportion than the power thus obtained, the locomotive will draw the

load up the incline without further assistance. It is, however, to be

observed, that in this case the load upon the engine must be less than

the amount which the adhesion of its working wheels with the railroad

is capable of drawing; for this adhesion must be adequate to the

traction of the same load up the incline, otherwise whatever increase

of power might be obtained by opening the throttle valve, the drawing

wheels would revolve without causing the load to advance. This method

has been generally practised upon the Liverpool and Manchester line in

the transport of passengers; and, indeed, it is the only method yet

discovered, which is consistent with the expedition necessary for that

species of traffic. The objections to this method are, the necessity

of maintaining a much higher pressure in the boiler than is sufficient

for the purposes of the load upon more level parts of the line.

In the practice of this method considerable aid may be derived also by

suspending the supply of feeding water during the ascent. It will be

recollected that a reservoir of cold water is placed in the tender

which follows the engine, and that the water is driven from this

reservoir into the boiler by a forcing-pump, which is worked by the

engine itself. This pump is so constructed that it will supply as much

cold water as is equal to the evaporation, so as to maintain

constantly the same quantity of water in the boiler. But it is

evident, on the other hand, that the supply of this water has a

tendency to check the rate of evaporation, since in being raised to

the temperature of the water with which it mixes, it must absorb a

considerable portion of the heat supplied by the fire. With a view to

accelerate the production of steam, therefore, in ascending the

inclines, the engine-man may suspend the action of the forcing-pump,

and thereby stop the supply of cold water to the boiler; the

evaporation will go on with increased rapidity, and the exhaustion of

water produced by it will be repaid by the forcing-pump on the next

level, or still more effectually on the next descending incline.

Indeed the feeding pump may be made to act in descending an incline if

necessary, when the action of the engine itself is suspended, and when

the train descends by its own gravity, in which case it will perform

the part of a brake upon the descending train.

This method, on railroads intended for passengers, may be successfully

applied on inclines which do not exceed 18 feet in a mile; and, with a

sacrifice of the expense of locomotive power, inclines so steep as 36

feet in a mile may be worked in this manner. As, however, the

sacrifice is considerable, it will, perhaps, be always better to work

the more steep inclines by assistant engines.

5. The mechanical connexion between the piston of the cylinder and the

points of contact of the working wheels with the road may be so

altered, upon arriving at the incline, as to give the piston a greater

power over the working wheels. This may be done in an infinite variety

of ways, but hitherto no method has been suggested sufficiently simple

to be applicable in practice; and even were any means suggested which

would accomplish this, unless the intensity of the impelling power

were at the same time increased, it would necessarily follow that the

speed of the motion would be diminished in exactly the same proportion

as the power of the piston over the working wheels would be increased.

Thus, on the inclined plane, which rises 55 feet per mile, upon the

Liverpool line, the speed would be diminished to nearly one fourth of

its amount upon the level.

Whatever be the method adopted to surmount inclined planes upon a

railway, inconvenience attends the descent upon them. The motion down

the incline by the force of gravity is accelerated; and if the train

be not retarded, a descent of any considerable length, even at a small

elevation, would produce a velocity which would be attended with great

danger. The shoe used to retard the descent down hills on turnpike

roads cannot be used upon railroads, and the application of brakes to

the faces of the wheels is likewise attended with some uncertainty.

The friction produced by the rapid motion of the wheel sometimes sets

fire to wood, and iron would be inadmissible. The action of the steam

on the piston may be reversed, so as to oppose the motion of the

wheels; but even this is attended with peculiar difficulty.

From all that has been stated, it will be apparent that, with our

present knowledge, considerable inclines are fatal to the profitable

performance on a railway, and even small inclinations are attended

with great inconvenience.[29]

[Footnote 29: A contrivance might be applied in changes of level in

railroads somewhat similar to locks in a canal. The train might be

rolled upon a platform which might be raised by machinery; and thus at

the change of level there would be as it were _steps_ from one level

to another, up which the loads would be lifted by any power applied to

work the machinery. The advantage in this case would be, that the

trains might be adapted to work always upon a level.]

(97.) To obtain from the locomotive steam engines now used on the

railway the most powerful effects, it is necessary that the load

placed on each engine should be very considerable. It is not possible,

with our present knowledge, to construct and work three locomotive

engines of this kind, each drawing a load of 30 tons, at the same

expense and with the same effect as one locomotive engine drawing 90

tons. Hence arises what must appear an inconvenience and difficulty in

applying these engines to one of the most profitable species of

transport--the transport of passengers. It is impracticable, even

between places of the most considerable intercourse to obtain loads of

passengers sufficiently great at each trip to maintain such an engine

working on a railway.[30] The difficulty of collecting so considerable

a number of persons, at any stated hour, to perform the journey, is

obvious; and therefore, the only method of removing the inconvenience

is _to cause the same engine which transports passengers also to

transport goods_, so that the goods may make up the requisite

supplement to the load of passengers. In this way, provided the

traffic in goods be sufficient, such engines may start with their full

complement of load, whatever be the number of passengers.

[Footnote 30: On the occasion of races held at Newton, a place about

15 miles from Liverpool, two engines were sent, with trains of

carriages, to take back to Liverpool the visitors to the races. Some

accident prevented one of the engines from working on the occasion,

and both trains were attached to the same engine: 800 persons were on

this occasion drawn by the single engine to Liverpool in the space of

about an hour.]

(98.) In comparing the extent of capital, and the annual expenditure

of the Liverpool and Manchester line, and adopting it as a modulus in

estimating the expenses of similar undertakings projected elsewhere,

there are several circumstances to which it is important to attend. I

have already observed on the large waste of capital in the item of

locomotive engines which ought to be regarded as little more than

experimental machines, leading to a rapid succession of improvements.

Most of these engines are still in good working order, but have been

abandoned for the reasons already assigned. Other companies will, of

course, profit by the experience which has been thus purchased at a

high price by the Liverpool Company. This advantage in favour of

future companies will go on increasing until such companies have their

works completed.

A large portion of the current expense of a line of railway is

independent of its length; and is little less for the line connecting

Liverpool and Manchester, than it would be for a line connecting

Birmingham with Liverpool or London.

The establishments of resident engineers, coach and wagon yards, &c.

at the extremities of the line, would be little increased by a very

great increase in the length of the railway; and the same observation

will apply to other heads of expenditure.

It has been the practice of the canal companies between Liverpool and

Manchester to warehouse the goods transported between these towns,

without any additional charge beyond the price of transport. The

Railway Company, in competing with the canals, were, of course,

obliged to offer like advantages: this compelled them to invest a

considerable amount of capital in the building of extensive

warehouses, and to incur the annual expense of porterage, salaries,

&c. connected with the maintenance of such storage. In a longer line

of railway such expenses (if necessary at all) would not be

proportionally increased.

(99.) The comparison of steam-transport with the transport by horses,

even when working on a railway, exhibits the advantage of this new

power in a most striking point of view. To comprehend these advantages

fully, it will be necessary to consider the manner in which animal

power is expended as a means of transport. The portion of the strength

of a horse available for the purpose of a load depends on the speed of

a horse's motion. To this speed there is a certain limit, at which the

whole power of the horse will be necessary to move his own body, and

at which, therefore, he is incapable of carrying any load; and, on the

other hand, there is a certain load which the horse is barely able to

support, but incapable of moving with any useful speed. Between these

two limits there is a certain rate of motion at which the useful

effect of the animal is greatest. In horses of the heavier class, this

rate of motion may be taken on the average as that of 2 miles an hour;

and in the lighter description of horses, 2-1/2 miles an hour. Beyond

this speed, the load which they are capable of transporting diminishes

in a very rapid ratio as the speed increases: thus, if 121 express the

load which a horse is able to transport a given distance in a day,

working at the rate of four miles an hour, the same horse will not be

able to transport more than the load expressed by 64, _the same

distance_, at 7 miles an hour; and, at 10 miles an hour, the load

which he can transport will be reduced to 25. The most advantageous

speed at which a horse can work being 2 miles an hour, it is found

that, at this rate, working for 10 hours daily, he can transport 12

tons, on a level railway, a distance of 20 miles; so that the whole

effect of a day's work may be expressed by 240 tons carried 1 mile.

But this rate of transport is inapplicable to the purposes of

travelling; and therefore it becomes necessary, when horses are the

moving power, to have carriages for passengers distinct from those

intended for the conveyance of goods; so that the goods may be

conveyed at that rate of speed at which the whole effect of the horse

will be the greatest possible; while the passengers are conveyed at

that speed which, whatever the cost, is indispensably necessary. The

weight of an ordinary mail-coach is about two tons; and, on a

tolerably level turnpike road, it travels at the rate of 10 miles an

hour. At this rate, the number of horses necessary to keep it

constantly at work, including the spare horses indispensably necessary

to be kept at the several stages, is computed at the rate of a horse

per mile. Assuming the distance between London and Birmingham at 100

miles, a mail-coach running between these two places would require 100

horses; making the journey to and from Birmingham daily. The

performance, therefore, of a horse working at this rate may be

estimated at 2 tons carried 2 miles per day, or 4 tons carried 1 mile

in a day. The force of traction on a good turnpike road is at least 20

times its amount on a level railroad. It therefore follows, that the

performance of a horse on a railroad will be 20 times the amount of

its performance on a common road under similar circumstances. We may,

therefore, take the performance of a horse working at 10 miles an

hour, on a level railroad, at 80 tons conveyed 1 mile daily.

The best locomotive engines used on the Liverpool railway are capable

of transporting 150 tons on a level railroad at the same rate; and,

allowing the same time for stoppage, its work per day would be 150

tons conveyed 200 miles, or 30,000 tons conveyed 1 mile; from which it

follows, that the performance of one locomotive engine of this kind is

equivalent to that of 7500 horses working on a good turnpike road, or

to 375 horses working on a railway. The consumption of fuel requisite

for this performance, with the most improved engines used at present

on the Manchester and Liverpool line, would be at the rate of

eight[31] ounces of coke per ton per mile, including the waste of fuel

incurred by the stoppages. Thus the daily consumption of fuel, under

such circumstances, would amount to 15000 lbs. of coke; and 2 lbs. of

coke daily would perform the work of one horse on a good turnpike

road; and 40 lbs. of coke daily would perform the work of one horse on

a railway.

[Footnote 31: In an experimental trip with a heavy train at 12 miles

an hour, I found the consumption of coke to be only _four_ ounces per

ton per hour. I believe, however, the practical consumption in

ordinary work to be very nearly eight ounces.]

In this comparison, the engine is taken at its most advantageous

speed, while horse-power is taken at its least advantageous speed, if

regard be only had to the total quantity of weight transported to a

given distance. But, in the case above alluded to, speed is an

indispensable element; and steam, therefore, possesses this great

advantage over horse power, that _its most advantageous speed is that

which is at once adapted to all the purposes of transport, whether of

passengers or of goods_.

(100.) The effects of steam compared with horse-power, at lower rates

of motion, will exhibit the advantages of the former, though in a

less striking degree. An eight-horse wagon commonly weighs 8 tons, and

travels at the rate of 2-1/2 miles an hour. Strong horses working in

this way can travel 8 hours daily; thus each horse performs 20 miles a

day. The performance, therefore, of each horse may be taken as

equivalent to 20 tons transported 1 mile; and his performance on a

railway being 20 times this amount, may be taken as equivalent to 400

tons transported 1 mile a day. The performance of a horse working in

this manner is, therefore, 5 times the performance of a horse working

at 10 miles an hour; the latter effecting only the performance of 4

tons transported 1 mile per day on a good turnpike road, or 80 tons on

a railway. We shall hence obtain the proportion of the performance of

horses working in wagons to that of a locomotive steam engine. Since 2

lbs. of coke are equivalent to the daily performance of a horse in a

mail-coach, and 40 lbs. on a railway, at 10 miles an hour, it follows

that 10 lbs. will be equivalent to the performance of a horse on a

turnpike road, and 200 lbs. on a railway, at 2-1/2 miles an hour.

Since a locomotive engine can perform the daily work of 7500

mail-coach horses, it follows that it performs the work of 1500 wagon

horses.

These results must be understood to be subject to modifications in

particular cases, and to be only average calculations. Different

steam-engines, as well as different horses, varying in their

performance to a considerable extent; and the roads on which horses

work being in different states of perfection, and subject to different

declivities, the performance must vary accordingly.

In the practical comparison, also, of the results of so powerful an

agent as steam applied on railways, with so slight a power as that of

horses on common roads, it must be considered that the great

subdivision of load, and frequent times of starting, operate in favour

of the performance of horses; inasmuch as it would oftener occur that

engines capable of transporting enormous weights would start with

loads inferior to their power, than would happen in the application of

horse-power, where small loads may start at short intervals. This, in

fact, constitutes a practical difficulty in the application of steam

engines on railroads; and will, perhaps, for the present, limit their

application to lines connecting places of great intercourse.

The most striking effect of steam power, applied on a railroad, is the

extreme speed of transport which is attained by it; and it is the more

remarkable, as this advantage never was foreseen before experience

proved it. When the Liverpool and Manchester line was projected, the

transport of heavy goods was the object chiefly contemplated; and

although an intercourse in passengers was expected, it was not

foreseen that this would be the greatest source of revenue to the

proprietors. The calculations of future projectors will, therefore, be

materially altered, and a great intercourse in passengers will be

regarded as a necessary condition for the prosperity of such an

undertaking.

If this advantage of speed be taken into account, horse-power can

scarcely admit of any comparison whatever with steam-power on a

railway. In the experiments which I have already detailed, it appears

that a steam engine is capable of drawing 90 tons at the rate of about

20 miles an hour, and that it could transport that weight twice

between Liverpool and Manchester in about 3 hours. Two hundred and

seventy horses working in wagons would be necessary to transport the

same load the same distance in a day. It may be objected, that this

was an experiment performed under favourable circumstances, and that

assistance was obtained at the difficult point of the inclined plane.

In the ordinary performance, however, of the engines drawing

merchandise, where great speed is not attempted, the rate of motion is

not less than 15 miles an hour. In the trains which draw passengers,

the chief difficulty of maintaining a great speed arises from the

stoppages on the road to take up and let down passengers. There are

two classes of carriages at present used: the first class stops but

once, at a point half-way between Liverpool and Manchester, for the

space of a few minutes. This class performs the thirty miles in an

hour and a half, and sometimes in 1 hour and 10 minutes. On the level

part of the road its common rate of motion is 27 miles an hour; and I

have occasionally marked its rate, and found it above 30 miles an

hour.

But these, which are velocities obtained in the regular working of the

engines for the transport of passengers and goods, are considerably

inferior to the power of the present locomotives with respect to

speed. I have made some experimental trips, in which more limited

loads were placed upon the engines, by which I have ascertained that

very considerably increased rates of motion are quite practicable. In

one experiment I placed a carriage containing 36 persons upon an

engine, with which I succeeded in obtaining the velocity of about 48

miles an hour, and I believe that an engine loaded only with its own

tender has moved over 15 miles in 15 minutes.

It will then perhaps be asked, if the engines possess these great

capabilities of speed, why they have not been brought into practical

operation on the railroad, where, on the other hand, the average speed

when actually in motion, does not exceed 25 miles an hour? In answer

to this it may be stated, that the distance of 30 miles between

Liverpool and Manchester is performed in an hour and a half, and that

10 trains of passengers pass daily between these places: the mail,

also, is transmitted three times a day between them. It is obvious

that any greater speed than this, in so short a distance, would be

quite needless. When, however, more extended lines of road shall be

completed, the circumstances will be otherwise, and the despatch of

mails especially will demand attention. Full trains of passengers,

commonly transported upon the Manchester railroad, weigh about 50 tons

gross: with a lighter load, a lighter and more expeditious engine

might be used. The expense of transport with such an engine would of

course be increased; but for this the increased expedition there

would be ample compensation. When, therefore, London shall have been

connected with Liverpool, by a line of railroad through Birmingham,

the commercial interest of these places will naturally direct

attention to the greatest possible expedition of intercommunication.

For the transmission of mails, doubtless, peculiar engines will be

built, adapted to lighter loads and greater speed. With such engines,

the mails, with a limited number of passengers, will be despatched;

and, apart from any possible improvement which the engines may

hereafter receive, and looking only at their present capabilities, I

cannot hesitate to express my conviction that such a load may be

transported at the rate of above 60 miles an hour. If we may indulge

in expectations of what the probable improvements of locomotive steam

engines may effect, I do not think that even double that speed is

beyond the limits of mechanical probability. On the completion of the

line of road from the metropolis to Liverpool we may, therefore,

expect to witness the transport of mails and passengers in the short

space of three hours. There will probably be about three posts a day

between these and intermediate places.

The great extension which the application of steam to the purpose of

inland transport is about to receive from the numerous railroads which

are already in progress, and from a still greater number of others

which are hourly projected, impart to these subjects of inquiry

considerable interest. Neither the wisdom of the philosopher, nor the

skill of the statistician, nor the foresight of the statesman is

sufficient to determine the important consequences by which the

realization of these schemes must affect the progress of the human

race. How much the spread of civilization, the diffusion of knowledge,

the cultivation of taste, and the refinement of habits and manners

depend upon the easy and rapid inter-mixture of the constituent

elements of society, it is needless to point out. Whilst population

exists in detached and independent masses, incapable of transfusion

amongst each other, their dormant affinities are never called into

action, and the most precious qualities of each are never imparted to

the other. Like solids in physics, they are slow to form combinations;

but when the quality of fluidity has been imparted to them, when their

constituent atoms are loosened by fusion, and the particles of each

flow freely through and among those of the other, then the affinities

are awakened, new combinations are formed, a mutual interchange of

qualities takes place, and compounds of value far exceeding those of

the original elements are produced. Extreme facility of intercourse is

the fluidity and fusion of the social masses, from whence such an

activity of the affinities results, and from whence such an

inestimable interchange of precious qualities must follow. We have,

accordingly, observed, that the advancement in civilization and the

promotion of intercourse between distant masses of people have ever

gone on with contemporaneous progress, each appearing occasionally to

be the cause or the consequence of the other. Hence it is that the

urban population is ever in advance of the rural in its intellectual

character. But, without sacrificing the peculiar advantages of either,

the benefits of intercourse may be extended to both, by the

extraordinary facilities which must be the consequence of the

locomotive projects now in progress. By the great line of railroad

which is in progress from London to Birmingham, the time and expense

of passing between these places will probably be halved, and the

quantity of intercourse at least quadrupled, if we consider only the

direct transit between the terminal points of the line; but if the

innumerable tributary streams which will flow from every adjacent

point be considered, we have no analogies on which to build a

calculation of the enormous increase of intercommunication which must

ensue.

Perishable vegetable productions necessary for the wants of towns must

at present be raised in their immediate suburbs; these, however, where

they can be transported with a perfectly smooth motion at the rate of

twenty miles an hour, will be supplied by the agricultural labourer

of more distant points. The population engaged in towns, no longer

limited to their narrow streets, and piled story over story in

confined habitations, will be free to reside at distances which would

now place them far beyond reach of their daily occupations. The

salubrity of cities and towns will thus be increased by spreading the

population over a larger extent of surface, without incurring the

inconvenience of distance. Thus the advantages of the country will be

conferred upon the town, and the refinement and civilization of the

town will spread their benefits among the rural population.[32]

[Footnote 32: Some of the preceding observations appeared in an

article contributed by me to the British and Foreign Review.]

(101.) The quantity of canal property in these countries gives

considerable interest to every inquiry which has for its object the

relative advantage of this mode of transport, compared with that of

railways, whether worked by horses or by steam-power; and this

interest has been greatly increased by the recent extension of railway

projects. This is a subject which I shall have occasion, in another

work, to examine in all its details; and, therefore, in this place I

shall advert to it but very briefly.

When a floating body is moved on a liquid, it will suffer a

resistance, which will depend partly upon the transverse section of

the part immersed, and partly on the speed with which it is moved. It

is evident that the quantity of the liquid which it must drive before

it will depend upon that transverse section, and the velocity with

which it will impel the liquid will depend upon its own speed. Now, so

long as the depth of its immersion remains the same, it is

demonstrable that the resistance will increase in proportion to the

square of the speed; that is, with a double velocity there will be a

fourfold resistance, with a triple velocity a ninefold resistance, and

so on. Again, if the part immersed should be increased or diminished

by any cause, the resistance, on that account alone, will be increased

or diminished in the same proportion.

From these circumstances it will be apparent that a vessel floating on

water, if moved with a certain speed, will require four times the

impelling force to carry it forward with double the speed, unless the

depth of its immersion be diminished as its speed is increased.

Some experiments which have been made upon canals with boats of a

peculiar construction, drawn by horses, have led to the unexpected

conclusion, that, after a certain speed has been attained, the

resistance, instead of being increased, has been diminished. This fact

is not at variance with the law of resistance already explained. The

cause of the phenomenon is found in the fact, that when the velocity

has attained a certain point, the boat gradually rises out of the

water; so that, in fact, the immersed part is diminished. The two

conditions, therefore, which determine the resistance, thus modify

each other: while the resistance is, on the one hand, increased in

proportion to the square of the speed, it is, on the other hand,

diminished in proportion to the diminution of the transverse section

of the immersed part of the vessel. It would appear that, at a certain

velocity, these two effects neutralise each other; and, probably, at

higher velocities the immersed part may be so much diminished as to

diminish the resistance in a greater degree than it is increased by

the speed, and thus actually to diminish the power of traction.

It is known that boats are worked on some of the Scottish canals, and

also on the canal which connects Kendal with Preston, by which

passengers are transported, at the rate of about ten miles an hour,

exclusive of the stoppages at the locks, &c. The power of horses,

exerted in this way, is, of course, exerted more economically than

they could be worked at the same speed on common roads; and, probably,

it is as economical as they would be worked by railroad. It is,

probably, more economical than the transport of passengers by steam

upon railroads; but the speed is considerably less, nor, from the

nature of the impelling power, is it possible that it can be

increased.

There is reason to suppose that a like effect takes place with steam

vessels. Upon increasing the power of the engines in some of the Post

Office steam packets, it has been found, that, while the time of

performing the same voyage is diminished, the consumption of fuel is

also diminished. Now, since the consumption of fuel is in the direct

ratio of the moving power, and the latter in the direct ratio of the

resistance, it follows that the resistance must in this case be

likewise diminished.

(102.) When a very slow rate of travelling is considered, the useful

effects of horse-power applied on canals is somewhat greater than the

effect of the same power applied on railways; but at all speeds above

three miles an hour, the effect on railways is greater; and when the

speed is considerable, the canal becomes wholly inapplicable, while

the railway loses none of its advantages. At three miles an hour, the

performance of a horse on a canal and a railway is in the proportion

of four to three to the advantage of the canal; but at four miles an

hour his performance on a railway has the advantage in very nearly the

same proportion. At six miles an hour, a horse will perform three

times more work on a railway than on a canal. At eight miles an hour,

he will perform nearly five times more work.

But the circumstance which, so far as respects passengers, must give

railways, as compared with canals, an advantage which cannot be

considered as less than fatal to the latter, is the fact, that the

great speed and cheapness of transit attainable upon a railway by the

aid of steam-power will always secure to such lines not only a

monopoly of the travelling, but will increase the actual amount of

that source of profit in an enormous proportion, as has been already

made manifest between Liverpool and Manchester. Before the opening of

the railway there were about twenty-five coaches daily running between

Liverpool and Manchester. If we assume these coaches on the average to

take ten persons at each trip, it will follow that the number of

persons passing daily between these towns was about 500. Let us, then,

assume that 3000 persons passed weekly. This gives in six months

78,000. In the six months which terminated on the 31st of December

1831, the number of passengers between the same towns, exclusive of

any taken up on the road, was 256,321; and if some allowance be made

for those taken up on the road, the number may be fairly stated at

300,000. At present there is but one coach on the road between

Liverpool and Manchester; and it follows, therefore, that, besides

taking the monopoly of the transit in travellers, the actual number

has been already increased in a fourfold proportion.

The monopoly of the transit of passengers thus secured to the line of

communication by railroad will always yield so large a profit as to

enable merchandise to be carried at a comparatively low rate.

In light goods, which require despatch, it is obvious that the

railroad will always command the preference; and the question between

that mode of communication and canals is circumscribed to the transit

of those classes of heavy goods in which even a small saving in the

cost of transport is a greater object than despatch.

(103.) The first effect which the Liverpool railroad produced on the

Liverpool and Manchester canals was a fall in the price of transport;

and at this time, I believe, the cost of transport per ton on the

railroads and on the canals is the same. It will, therefore, be

naturally asked, this being the case, why the greater speed and

certainty of the railroad does not in every instance give it the

preference, and altogether deprive the canals of transport? This

effect, however, is prevented by several local and accidental causes,

as well as by direct influence and individual interest. A large

portion of the commercial and manufacturing population of Liverpool

and Manchester have property invested in the canals, and are deeply

interested to sustain them in opposition to the railway. Such persons

will give the preference to the canals in their own business, and will

induce those over whom they have influence to do so in every case

where speed of transport is not absolutely indispensable.

Besides these circumstances, the canal communicates immediately with

the shipping at Liverpool, and it ramifies in various directions

through Manchester, washing the walls of many of the warehouses and

factories for which the goods transported are destined. The

merchandise is thus transferred from the shipping to the boat, and

brought directly to the door of its owner, or _vice versâ_. If

transported by the railway, on the other hand, it must be carried to

the station at one extremity; and, when transported to the station at

the other, it has still to be carried to its destination in different

parts of the town.

These circumstances will sufficiently explain why the canals still

retain, and may probably continue to retain, a share of the traffic

between these great marts.

CHAPTER XI.

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.

Railways and Turnpike Roads compared. -- Mr. Gurney's inventions.

-- His Locomotive Steam Engine. -- Its performances. --

Prejudices and errors. -- Committee of the House of Commons. --

Convenience and safety of Steam Carriages. -- Hancock's Steam

Carriage. -- Mr. N. Ogle. -- Trevithick's invention. --

Proceedings against Steam Carriages. -- Turnpike Bills. -- Steam

Carriage between Gloucester and Cheltenham. -- Its

discontinuance. -- Report of the Committee of the Commons. --

Present State and Prospects of Steam Carriages.

(104.) We have hitherto confined our observations to steam-power as a

means of transport applied on railways, but modern speculation has not

stopped here. Several attempts have been made, and some of them

attended with considerable success, to work steam-carriages on

turnpike roads. The practicability of this project has been hitherto

generally considered to be very questionable; but if we carry back our

view to the various epochs in the history of the invention of the

steam engine, we shall find the same doubt, and the same difficulty,

started at almost every important step in its progress. In comparing

the effect of a turnpike road with that of a railway, there are two

circumstances which obviously give facility and advantage to the

railway. One is, that the obstructions to the rolling motion of the

wheels, produced by the inequalities of the surface, are very

considerably less on a railway than on a road; less in the proportion

of at least 1 to 20. This proportion, however, must depend much on the

nature of the road with which the railway is compared. It is obvious

that a well-constructed road will offer less resistance than one ill

constructed; and it is ascertained that the resistance of a

Macadamised road is considerably more than that of a road well paved

with stones: the decision of this question, therefore, must involve

the consideration of another, viz. whether roads may not be

constructed by pavement or otherwise, smoother and better adapted to

carriages moved in the manner of steam-carriages than the roads now

used for horse-power?

But besides the greater smoothness of railroads compared with turnpike

roads, they have another advantage, which we suspect to have been

considerably exaggerated by those who have opposed the project for

steam-carriages on turnpike roads. One of the laws of adhesion, long

since developed by experiment, and known to scientific men, is, that

it is greater between the surfaces of bodies of the same nature than

between those of a different nature. Thus between two metals of the

same kind it is greater than between two metals of different kinds.

Between two metals of any kind it is greater than between metal and

stone, or between metal and wood. Hence, the wheels of steam-carriages

running on a railroad have a greater adhesion with the road, and

therefore offer a greater resistance to slip round without the advance

of the carriage, than wheels would offer on a turnpike road; for on a

railroad the iron tire of the wheel rests in contact with the iron

rail, while on a common road the iron tire rests in contact with the

surface of stone, or whatever material the road may be composed of.

Besides this, the dust and loose matter which necessarily collect on a

common road, when pressed between the wheels and the solid base of the

road act somewhat in the manner of rollers, and give the wheels a

greater facility to slip than if the road were swept clean, and the

wheels rested in immediate contact with its hard surface. The truth of

this observation is illustrated on the railroads themselves, where the

adhesion is found to be diminished whenever the rails are covered with

any extraneous matter, such as dust or moist clay. Although the

adhesion of the wheels of a carriage with a common road, however, be

less than those of the wheels of a steam-carriage with a railroad, yet

still the actual adhesion on turnpike roads is greater in amount than

has been generally supposed, and is quite sufficient to propel

carriages dragging after them loads of large amount.

The relative facility with which carriages are propelled on railroads

and turnpike roads equally affects any moving power, whether that of

horses or steam engines; and whether loads be propelled by the one

power or the other, the railroad, as compared with the turnpike road,

will always possess the same proportionate advantage; and a given

amount of power, whether of the one kind or the other, will always

perform a quantity of work less in the same proportion on a turnpike

road than on a railroad. But, on the other hand, the expense of

original construction, and of maintaining the repairs of a railroad,

is to be placed against the certain facility which it offers to

draught.

In the attempts which have been made to adapt locomotive engines to

turnpike roads, the projectors have aimed at the accomplishment of two

objects: first, the construction of lighter and smaller engines; and,

secondly, increased power. These ends, it is plain, can only be

attained, with our present knowledge, by the production of steam of

very high temperature and pressure, so that the smallest volume of

steam shall produce the greatest possible mechanical effect. The

methods of propelling the carriage have been in general similar to

that used in the railroad engines, viz. either by cranks placed on the

axles, the wheels being fixed upon the same axles, or by connecting

the piston-rods with the spokes of the wheels, as in the engine

represented in fig. 55. In some carriages, the boiler and moving

power, and the body of the carriage which bears the passengers, are

placed on the same wheels. In others, the engine is placed on a

separate carriage, and draws after it the carriage which transports

the passengers, as is always the case on railways.

The chief difference between the steam engines used on railways, and

those adapted to propel carriages on turnpike roads, is in the

structure of the boiler. In the latter it is essential that, while

the power remains undiminished, the boiler should be lighter and

smaller. The accomplishment of this has been attempted by various

contrivances for so distributing the water, as to expose a

considerable quantity of surface in contact with it to the action of

the fire; spreading it in thin layers on flat plates; inserting it

between plates of iron placed at a small distance asunder, the fire

being admitted between the intermediate plates; dividing it into small

tubes, round which the fire has play; introducing it between the

surfaces of cylinders placed one within another, the fire being

admitted between the alternate cylinders,--have all been resorted to

by different projectors.

(105.) First and most prominent in the history of the application of

steam to the propelling of carriages on turnpike roads, stands the

name of Mr. GOLDSWORTHY GURNEY, a medical gentleman and scientific

chemist, of Cornwall. In 1822, Mr. _Gurney_ succeeded Dr. Thompson as

lecturer on chemistry at the Surrey Institution; and, in consequence

of the results of some experiments on heat, his attention was directed

to the project of working steam carriages on common roads; and since

1825 he has devoted his exertions in perfecting a steam engine capable

of attaining the end he had in view. Numerous other projectors, as

might have been expected, have followed in his wake. Whether they, or

any of them, by better fortune, greater public support, or more

powerful genius, may outstrip him in the career on which he has

ventured, it would not, perhaps, at present, be easy to predict. But

whatever be the event, to Mr. _Gurney_ is due, and will be paid, the

honour of first proving the practicability of the project; and in the

history of the adaptation of the locomotive engine to common roads,

his name will stand before all others in point of time, and the

success of his attempts will be recorded as the origin and cause of

the success of others in the same race.

The incredulity, opposition, and even ridicule, with which the project

of Mr. _Gurney_ was met, are very remarkable. His views were from the

first opposed by engineers, without one exception. The contracted

habit of mind, sometimes produced by an education chiefly, if not

exclusively, directed to a merely practical object, subsequently

confirmed by exclusively practical pursuits, may, perhaps, in some

degree, account for this. But, I confess, it has not been without

surprise that I have observed, during the last ten years, the utter

incredulity which has prevailed among men of general science on this

subject,--an incredulity which the most unequivocal practical proof

has scarcely yet dispelled. "Among scientific men," says Mr. _Gurney_,

"my opinion had not a single supporter, with the exception of the late

Dr. _Wollaston_."

The mistake which so long prevailed in the application of locomotives

on railroads, and which, as we have shown, materially retarded the

progress of that invention, was shared by Mr. _Gurney_. Without

reducing the question to the test of experiment, he took for granted,

in his first attempts, that the adhesion of the wheels with the road

was too slight to propel the carriage. He was assured, he says, by

eminent engineers, that this was a point settled by actual experiment.

It is strange, however, that a person of his quickness and sagacity

did not inquire after the particulars of these "actual experiments."

So, however, it was; and, taking for granted the inability of the

wheels to propel, he wasted much labour and skill in the contrivance

of levers and propellers, which acted on the ground in a manner

somewhat resembling the feet of horses, to drive the carriage forward.

After various fruitless attempts of this kind, the experience acquired

in the trials to which they gave rise at last forced the truth upon

his notice, and he found that the adhesion of the wheels was not only

sufficient to propel the carriage heavily laden on level roads, but

was capable of causing it to ascend all the hills which occur on

ordinary turnpike roads. In this manner it ascended all the hills

between London and Barnet, London and Stanmore, Stanmore Hill,

Brockley Hill, and mounted Old Highgate Hill, the last at one point

rising one foot in nine.

It would be foreign to my present object to detail minutely all the

steps by which Mr. _Gurney_ gradually improved his contrivance. This,

like other inventions, has advanced by a series of partial failures;

but it has at length attained that state, in which, by practice alone,

on a more extensive scale, a further degree of perfection can be

obtained.

(106.) The boiler of this engine is so constructed that there is no

part of it, not even excepting the grate-bars, in which metal exposed

to the action of the fire is out of contact with water. If it be

considered how rapidly the action of an intense furnace destroys metal

when water is not present to prevent the heat from accumulating, the

advantage of this circumstance will be appreciated. I have seen the

bars of a new grate, never before used, melted in a single trip

between Liverpool and Manchester; and the inventor of another form of

locomotive engine has admitted to me that his grate-bars, though of a

considerable thickness, would not last more than a week. In the boiler

of Mr. _Gurney_, the grate-bars themselves are tubes filled with

water, and form, in fact, a part of the boiler itself. This boiler

consists of three strong metal cylinders placed in a horizontal

position one above the other. A section, made by a perpendicular or

vertical plane, is represented in fig. 62. The ends of the three

cylinders, just mentioned, are represented at D, H, and I. In the side

of the lowest cylinder D are inserted a row of tubes, a ground plan of

which is represented in fig. 63. These tubes, proceeding from the side

of the lowest cylinder D, are inclined slightly upwards, for a reason

which I shall presently explain. From the nature of the section, only

one of these tubes is visible in fig. 62. at C. The other extremities

of these tubes at A are connected with the same number of upright

tubes, one of which is expressed at E. The upper extremities G of

these upright tubes are connected with another set of tubes K, equal

in number, proceeding from G, inclining slightly upwards, and

terminating in the second cylinder H.

[Illustration: _Fig. 62._]

[Illustration: _Fig. 63._]

An end view of the boiler is exhibited in fig. 64., where the three

cylinders are expressed by the same letters. Between the cylinders D

and H there are two tubes of communication B, and two similar tubes

between the cylinders H and I. From the nature of the section these

appear only as a single tube in fig. 62. From the top of the cylinder

I proceeds a tube N, by which steam is conducted to the engine.

[Illustration: _Fig. 64._]

It will be perceived that the space F is enclosed on every side by a

grating of tubes, which have free communication with the cylinders D

and H, which cylinders have also a free communication with each other

by the tubes B. It follows, therefore, that if water be supplied to

the cylinder I, it will descend through the tubes, and first filling

the cylinder D and the tubes C, will gradually rise in the tubes B and

E, will next fill the tubes K and the cylinder H. The grating of water

pipes C E K forms the furnace, the pipes C being the fire-bars, and

the pipes E and K being the back and roof of the stove. The fire-door,

for the supply of fuel, appears at M, fig. 64. The flue issuing

between the tubes F is conducted over the tubes K, and the flame and

hot air are carried off through a chimney. That portion of the heat of

the burning fuel, which in other furnaces destroys the bars of the

grate, is here expended in heating the water contained in the tubes C.

The radiant heat of the fire acts upon the tubes K, forming the roof

of the furnace, on the tube E at the back of it, and partially on the

cylinders D and H, and the tubes B. The draft of hot air and flame

passing into the flue at A, acts upon the posterior surfaces of the

tubes E, and the upper sides of the tubes K, and finally passes into

the chimney.

As the water in the tubes C E K is heated, it becomes specifically

lighter than water of a less temperature, and consequently acquires a

tendency to ascend. It passes, therefore, rapidly into H. Meanwhile

the colder portions descend, and the inclined positions of the tubes C

and K give play to this tendency of the heated water, so that a

prodigiously rapid circulation is produced, when the fire begins to

act upon the tubes. When the water acquires such a temperature that

steam is rapidly produced, steam bubbles are constantly formed in the

tubes surrounding the fire; and if these remained stationary in the

tubes, the action of the fire would not only decompose the steam, but

render the tubes red hot, the water not passing through them to carry

off the heat. But the inclined position of the tubes, already noticed,

effectually prevents this injurious consequence. A steam bubble which

is formed either in the tubes C or K, having a tendency to ascend

proportional to its lightness as compared with water, necessarily

rushes upwards; if in C towards A, and if in K towards H. But this

motion of the steam is also aided by the rapid circulation of the

water which is continually maintained in the tubes, as already

explained, otherwise it might be possible, notwithstanding the levity

of steam compared with water, that a bubble might remain in a narrow

tube without rising. I notice this more particularly, because the

burning of the tubes is a defect which has been erroneously, in my

opinion, attributed to this boiler. To bring the matter to the test of

experiment, I have connected two cylinders, such as D and H, by a

system of glass tubes, such as represented at C E K. The rapid and

constant circulation of the water was then made evident: bubbles of

steam were formed in the tubes, it is true; but they passed with great

rapidity into the upper cylinder, and rose to the surface, so that the

glass tubes never acquired a higher temperature than that of the water

which passed through them.

This I conceive to be the chief excellence of Mr. _Gurney's_ boiler.

It is impossible that any part of the metal of which it is formed can

receive a greater temperature than that of the water which it

contains; and that temperature, as is obvious, can be regulated with

the most perfect certainty and precision. I have seen the tubes of

this boiler, while exposed to the action of the furnace, after that

action has continued for a long period of time, and I have never

observed the soot which covers them to redden, as it would do if the

tube attained a certain temperature.

Every part of the boiler being cylindrical, it has the form which,

mechanically considered, is most favourable to strength, and which,

within given dimensions, contains the greatest quantity of water. It

is also free from the defects arising from unequal expansion, which

are found to be most injurious in tubular boilers. The tubes C and K

can freely expand in the direction of their length, without being

loosened at their joints, and without straining any part of the

apparatus; the tubes E, being short, are subject to a very slight

degree of expansion; and it is obvious that the long tubes, with which

they are connected, will yield to this without suffering a strain, and

without causing any part of the apparatus to be loosened.

When water is converted into steam, any foreign matter which may be

combined with it is disengaged, and is deposited on the bottom of the

vessel in which the water is evaporated. All boilers, therefore,

require occasional cleansing, to prevent the crust thus formed from

accumulating; and this operation, for obvious reasons, is attended

with peculiar difficulty in tubular boilers. In the case before us,

the crust of deposited matter would gather and thicken in the tubes C

and K, and if not removed, would at length choke them. But besides

this, it would be attended with a still worse effect; for, being a bad

conductor, it would intercept the heat in its transit from the fire to

the water and would cause the metal of the tube to become unduly

heated. Mr. _Gurney_ of course foresaw this inconvenience, and

contrived an ingenious chemical method of removing it by occasionally

injecting through the tubes such an acid as would combine with the

deposite, and carry it away. This method was perfectly effectual; and

although its practical application was found to be attended with

difficulty in the hands of common workmen, Mr. _Gurney_ was persuaded

to adhere to it by the late Dr. _Wollaston_, until experience proved

the impossibility of getting it effectually performed, under the

circumstances in which boilers are commonly used. Mr. _Gurney_ then

adopted the more simple, but not less effectual, method of removing

the deposite by mechanical means. Opposite the mouths of the tubes,

and on the other side of the cylinders D and H, are placed a number of

holes, which, when the boiler is in use, are stopped by pieces of

metal screwed into them. When the tubes require to be cleaned these

stoppers are removed, and an iron scraper is introduced through the

holes into the tubes, which being passed backwards and forwards,

removes the deposite. The boiler may be thus cleaned by a common

labourer in half a day, at an expense of about 1_s._ 6_d._

The frequency of the periods at which a boiler of this kind requires

cleaning must depend, in a great degree, on the nature of the water

which is used; one in daily use with the water of the river Thames

would not require cleaning more than once in a month. Mr. _Gurney_

states that with water of the most unfavourable description, once a

fortnight would be sufficient.

(107.) In the more recent boilers constructed by Mr. _Gurney_, he has

maintained the draught through the furnace, by the method of

projecting the waste steam into the chimneys; a method so perfectly

effectual, that it is unlikely to be superseded by any other. The

objection which has been urged against it in locomotive engines,

working on turnpike roads, is, that the noise which it produces has a

tendency to frighten horses.

In the engines on the Liverpool road, the steam is allowed to pass

directly from the eduction pipe of the cylinder to the chimney, and it

there escapes in puffs corresponding with the alternate motion of the

pistons, and produces a noise, which, although attended with no

inconvenience on the railroad, would certainly be objectionable on

turnpike roads. In the engine used in Mr. _Gurney's_ steam-carriage,

the steam which passes from the cylinders is conducted to a

receptacle, which he calls a blowing box. This box serves the same

purpose as the upper chamber of a smith's bellows. It receives the

steam from the cylinders in alternate puffs, but lets it escape into

the chimney in a continued stream by a number of small jets. Regular

draught is by this means produced, and no noise is perceived. Another

exit for the steam is also provided, by which the conductor is enabled

to increase or diminish, or to suspend altogether, the draught in the

chimney, so as to adapt the intensity of the fire to the exigencies of

the road. This is a great convenience in practice; because, on some

roads, a draught is scarcely required, while on others a powerful

blast is indispensable.

Connected with this blowing box, is another ingenious apparatus of

considerable practical importance. The pipe through which the water

which feeds the boiler is conducted to it from the tank is carried

through this blowing box, within which it is coiled in a spiral form,

so that an extensive thread of the feeding water is exposed to the

heat of the waste steam which has escaped from the cylinders, and

which is enclosed in this blowing box. In passing through this pipe

the feeding water is raised from the ordinary temperature of about 60°

to the temperature of 212°. The fuel necessary to accomplish this is,

therefore, saved, and the amount of this is calculated at 1/6th of all

that is necessary to evaporate the water. Thus, 1/6th of the expense

of fuel is saved. But, what is much more important in a locomotive

engine, a portion of the weight of the engine is saved without any

sacrifice of its power. There is still another great advantage

attending this process. The feeding water in the worm just mentioned,

while it takes up the heat from the surrounding steam in the blowing

box, condenses 1/6th of the waste steam, which is thence conducted to

the tank, from which the feeding water is pumped, saving in this

manner 1/6th in weight and room of the water necessary to be carried

in the carriage for feeding the boiler.[33]

[Footnote 33: In boilers constructed for stationary purposes, or for

steam navigation, the steam-pipe, after it has passed through the

blowing box, is continued and made to form a series of returned flues

over the boiler, so as to take up the waste heat after it has passed

the boiler, and before it reaches the chimney. But in locomotive

engines for common roads, it has been found by experience, that the

power gained by the waste heat is not sufficient to propel the weight

of the material necessary for taking it up.]

So far as the removal of all inconvenience arising from noise, this

contrivance has been proved by experience to be perfectly

effectual.[34]

[Footnote 34: See Report of the Commons.]

In all boilers, the process of violent ebullition causes a state of

agitation in the water, and a number of counter currents, by which, as

the steam is disengaged from the surface of the water, it takes with

it a considerable quantity of water in mechanical mixture. If this be

carried through the cylinders, since it possesses none of the

qualities of steam, and adds nothing to the power of the vapour with

which it is combined, it causes an extensive waste of heat and water,

and produces other injurious effects. In every boiler therefore, some

means should be provided for the separation of the water thus

suspended in the steam, before the steam is conducted to the cylinder.

In ordinary plate boilers, the large space which remains above the

surface of the water serves this purpose. The steam being there

subject to no agitation or disturbance, the water mechanically

suspended in it descends by its own gravity, and leaves pure steam in

the upper part. In the small tubular boilers, this has been a matter,

however, of greater difficulty. The contracted spaces in which the

ebullition takes place, causes the water to be mixed with the steam in

a greater quantity than could happen in common plate boilers: and the

want of the same steam-room renders the separation of the water from

the steam a matter of some difficulty. These inconveniences have been

overcome by a succession of contrivances of great ingenuity. I have

already described the rapid and regular circulation effected by the

arrangement of the tubes. By this a regularity in the currents is

established, which alone has a tendency to diminish the mixture of

water with the steam. But in addition to this, a most effectual method

of separation is provided in the vessel I, which is a strong iron

cylinder of some magnitude, placed out of the immediate influence of

the fire. A partial separation of the steam from the water takes place

in the cylinder H; and the steam with the water mechanically suspended

in it, technically called moist steam, rises into the _separator_ I.

Here, being free from all agitation and currents, and being, in fact,

quiescent, the particles of water fall to the bottom, while the pure

steam remains at the top. This separator, therefore, serves all the

purposes of the steam-room above the surface of the water in the large

plate boilers. The dry steam is thus collected and ready for the

supply of the engine through the tube N, while the water, which is

disengaged from it, is collected at the bottom of the separator, and

is conducted through the tube T to the lowest vessel D, to be again

circulated through the boiler.

The pistons of the engine work on the axles of the hind wheels of the

carriage which bears the engine, by cranks, as in the locomotives on

the Manchester railway, so that the axle is kept in a constant state

of rotation while the engine is at work. The wheels placed on this

axle are not permanently fixed or keyed upon it, as in the Manchester

locomotives; but they are capable of turning upon it in the same

manner as ordinary carriage wheels. Immediately within these wheels

there are fixed upon the axles two projecting spokes or levers, which

revolve with the axle, and which take the position of two opposite

spokes of the wheel. These may be occasionally attached to the wheel

or detached from it; so that they are capable of compelling the wheels

to turn with the axle, or leaving the axle free to turn independent of

the wheel, or the wheel independent of the axle, at the pleasure of

the conductor. It is by these levers that the engine is made to propel

either or both of the wheels. If both pairs of spokes are thrown into

connexion with the wheels, the crank shaft or axle will cause both

wheels to turn with it, and in that case the operation of the carriage

is precisely the same as those of the locomotives already described

upon the Liverpool and Manchester line; but this is rarely found to be

necessary, since the adhesion of one wheel with the road is generally

sufficient to propel the carriage, and consequently only one pair of

these fixed levers are generally used, and the carriage propelled by

only one of the two hind wheels. The fore wheels of the carriage turn

upon a pivot similar to those of a four-wheeled coach. The position of

these wheels is changed at pleasure by a simple pinion and circular

rack, which is moved by the conductor, and in this manner the carriage

is guided with precision and facility.

The force of traction necessary to propel a carriage upon common

roads must vary with the variable quality of the road, and

consequently the propelling power, or the pressure upon the pistons of

the engine, must be susceptible of a corresponding variation; but a

still greater variation becomes necessary from the undulations and

hills which are upon all ordinary roads. This necessary change in the

intensity of the impelling power is obtained by restraining the steam

in the boiler by the throttle valve, as already described in the

locomotive engines on the railroad. This principle, however, is

carried much further in the present case. The steam in the boiler may

be at a pressure of from 100 to 200 lbs. on the square inch; while the

steam on the working piston may not exceed 30 or 40 lbs. on the inch.

Thus an immense increase of power is always at the command of the

conductor; so that when a hill is encountered, or a rough piece of

road, he is enabled to lay on power sufficient to meet the exigency of

the occasion.

The two difficulties which have been always apprehended in the

practical working of steam carriages upon common roads are, first, the

command of sufficient power for hills and rough pieces of road; and,

secondly, the apprehended insufficiency of the adhesion of the wheels

with the road to propel the carriage. The former of these difficulties

has been met by allowing steam of a very great pressure to be

constantly maintained in the boiler with perfect safety. As to the

second, all experiments tend to show that there is no ground for the

supposition that the adhesion of the wheels is in any case

insufficient for the purposes of propulsion. Mr. _Gurney_ states, that

he has succeeded in driving carriages thus propelled up considerable

hills on the turnpike roads about London. He made a journey to Barnet

with only one wheel attached to the axle, which was found sufficient

to propel the carriage up all the hills upon that road. The same

carriage, with only one propelling wheel, also went to Bath, and

surmounted all the hills between Cranford Bridge and Bath, going and

returning.

A double stroke of the piston produces one revolution of the

propelling wheels, and causes the carriage to move through a space

equal to the circumference of those wheels. It will therefore be

obvious, that the greater the diameter of the wheels, the better

adapted the carriage is for speed; and, on the other hand, wheels of

smaller diameter are better adapted for power. In fact, the propelling

power of an engine on the wheels will be in the inverse proportion to

their diameter. In carriages designed to carry great weights at a

moderate speed, smaller wheels will be used; while in those intended

for the transport of passengers at considerable velocities, wheels of

at least 5 feet in diameter are most advantageous.

Among the numerous popular prejudices to which this new 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 most clearly and successfully exposed in the evidence taken

before the committee of the House of Commons upon steam carriages. It

is there fully demonstrated, not only that carriages thus propelled

did 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 fully 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. In that report they will not only

find demonstrative evidence that the introduction of steam carriages

will materially contribute to the saving in the wear of turnpike

roads, but also that the practicability of working such carriages with

a great saving to the public--with great increase of speed and other

conveniences to the traveller--is fully established.

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 with the weight of a

common stage coach, with 4 horses inclusive.

(108.) 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 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.