described is not wanting in yet another class of machine-tools, namely,
those employed in converting timber into the forms required to adapt it
for the uses to which it is so extensively applied. And for popular
illustration, this class of tools presents the special advantage of
being readily understood as regards their purpose and mode of action,
while their simplicity in these respects does not prevent them from
showing the advantages of machine over hand labour. Everybody is
familiar with the up-and-down movement of a common saw, and in the
machine for sawing balks of timber into planks, represented in Fig. 36,
this reciprocating motion is retained, but there are a number of saws
fixed parallel to each other in a strong frame, at a distance
corresponding to the thickness of the planks. The saws are not placed
with their cutting edges quite upright, but these are a little more
forward at the top, so that as they descend they cut into the wood, but
move upwards without cutting, for the teeth then recede from the line of
the previous cut, while in the meantime the balk is pushed forward ready
for the next descent of the saw-frame. This pushing forward, or
_feeding_, of the timber is accomplished by means of ratchet-wheels,
which are made to revolve through a certain space after each descent of
the saw-frame, and, by turning certain pinions, move forward the
carriage on which the piece of timber is firmly fixed, so that when the
blades of the saws are beginning the next descent they are already in
contact with the edge of the former cut. To prevent the blades from
moving with injurious friction in the saw-cuts, these last are made of
somewhat greater width than the thickness of the blades, by the simple
plan of bending the teeth a little on one side and on the other
alternately. The rapidity with which the machine works, depends of
course on the kind of wood operated upon, but it is not unusual for such
a machine to make more than a hundred cuts in the minute. The figure
shows the machine as deriving its motion by means of a strap passing
over a drum, from shafting driven by a steam engine. This is the usual
plan, but sometimes the steam power is applied directly, by fixing the
piston-rod of a steam cylinder to the top of the saw-frame, and
equalizing the motion by a fly-wheel on a shaft, turned by a crank and
connecting-rod.
A very effective machine for cutting pieces of wood of moderate
dimensions is the _Circular Saw_, represented in Fig. 37. Here there is
a steel disc, having its rim formed into teeth; and the disc is made to
revolve with very great speed, in some cases making as many as five
hundred turns in a minute, or more than eight in a second. On the bench
is an adjustable straight guide, or fence, and when this has been fixed,
the workman has only to press the piece of wood against it, and push the
wood at the same time towards the saw, which cuts it at a very rapid
rate. Sometimes the circular saw is provided with apparatus by which the
machine itself pushes the wood forwards, and the only attention required
from the workman is the fixing of the wood upon the bench, and the
setting of the machine in gear with the driving-shaft. Similar saws are
used for squaring the ends of the iron rails for railways, two circular
saws being fixed upon one axle at a distance apart equal to the length
of the rails. The axle is driven at the rate of about 900 turns per
minute, and the iron rail is brought up parallel to the axle, being
mounted on a carriage, and still red hot, when the two ends are cut at
the same time by the circular saws, the lower parts of which dip into
troughs of water to keep them cool.
[Illustration:
FIG. 38.—_Pit-Saw._
]
[Illustration:
FIG. 39.—_Box Tunnel._
]
RAILWAYS.
[Illustration:
FIG. 40.—_Coal-pit, Salop._
]
Towards the end of last century, tramways formed by laying down narrow
plates of iron, were in use at mines and collieries in several parts of
England. These plates had usually a projection or flange on the inner
edge, thus—L, in order to keep the waggons on the track, for the wheels
themselves had no flange, but were of the kind used on ordinary roads.
These flat tramways were found liable to become covered up with dirt and
gravel, so that the benefit which ought to have been obtained from their
smoothness was in a great measure lost. _Edge rails_ were, therefore,
substituted, and the wheels were kept on the rails by having a _flange_
cast on the inner edge of the rim. The rails were then always made of
cast iron, for, although they were very liable to break, the great cost
of making them of wrought iron prevented that material from being used
until 1820, when the method of forming rails of malleable iron by
rolling came into use. The first time a tramway was used for the
conveyance of passengers was in 1825, when the Stockton and Darlington
Railway was opened—a length of thirty-seven miles. It appears that the
carriages were at first drawn by horses, although locomotives were used
on this and other colliery lines for dragging, at a slow rate, trains of
mineral waggons. At that time engineers were exercising their ingenuity
in overcoming a difficulty which never existed by devising plans for
giving tractive power to the locomotive through the instrumentality of
rack-work rails. It never occurred to them to first try whether the
adhesion of the smooth wheel to the smooth rail was not sufficient for
the purpose. During the first quarter of the present century the greater
part of the goods and much passenger traffic was monopolized by the
canals. It is quoted, as a proof of the careless manner in which this
service was performed, that the transport of bales of cotton from
Liverpool to Manchester sometimes occupied twice the length of time
required in their voyage across the Atlantic. When an Act of Parliament
authorizing the construction of a railway between Liverpool and
Manchester was applied for, the canal companies succeeded in retarding,
by their influence, the passing of that Act for two years. It was
passed, however, in 1828, and the construction of the line was proceeded
with. This line was at first intended only for the conveyance of goods,
especially of cotton and cotton manufactures, and the waggons were to be
drawn by horses. When the line was nearly finished the idea of employing
horses was, at the instigation of Mr. George Stephenson, abandoned in
favour of steam power. The directors were divided in opinion as to
whether the carriage should be dragged by ropes wound on large drums by
stationary engines, or whether locomotives should be employed. Finally,
the latter plan was adopted, and it was also suggested that passengers
might be carried. The directors offered a prize for the best locomotive,
and the result has been already mentioned. In the light of our
experience since that time, it is curious to read of the doubts then
entertained by skilful engineers about the success of the locomotive. In
a serious treatise on the subject, one eminent authority hoped “that he
might not be confounded with those hot-brained enthusiasts who
maintained the possibility of carriages being driven by a steam engine
on a railway at such a speed as twelve miles an hour.” When the “Rocket”
had accomplished the unprecedented velocity of twenty-nine miles an
hour, and the railway was opened for passengers as well as goods, the
thirty stage coaches daily plying between Liverpool and Manchester found
their occupation gone, and all ceased to run except one, which had to
depend on the roadside towns only, while the daily number of passengers
between the two cities rose at once from 500 to 1,600. In that
delightful book, Smiles’s “Life of George Stephenson,” may be found most
interesting details of the difficulties attending the introduction of
railways, especially with regard to the construction of this first
important line. Mr. Smiles relates how the promoters of the scheme
struggled against “vested interests;” how the canal proprietors,
confident at first of a secure and continuous enjoyment of their
monopoly, ridiculed the proposed railway, and continued their exorbitant
charges and tardy conveyance, pocketing in profits the prime cost of
their canal about every three years; how, roused into active opposition,
they did all in their power to thwart the new scheme; how the Lord Derby
and the Lord Sefton of that day, and other landowners, offered every
resistance to the surveyors; how the Duke of Bridgewater’s farmers would
not allow them to enter their fields, and the Duke’s gamekeepers had
orders to shoot them; how even a clergyman threatened them with personal
violence, and they had to do their work by stealth, while the reverend
gentleman was conducting the services in his church; how newspaper and
other writers declared that the locomotives would kill the birds,
prevent cows from grazing and hens from laying, burn houses, and cause
the extinction of the race of horses. All the civil engineers scouted
the idea of a locomotive railway, and Stephenson was held up to derision
as an ignoramus and a maniac by the “most eminent lawyers,” and the most
advanced and “respectable” professional C.E.s of the time. An article
appeared in the “Quarterly Review,” very favourable to the construction
of railways, but remarking in reference to a proposed line between
London and Woolwich: “What can be more palpably absurd and ridiculous
than the prospect held out of locomotives travelling _twice as fast as
stage coaches_! We should as soon expect the people of Woolwich to
suffer themselves to be fired off upon one of Congreve’s _ricochet_
rockets as trust themselves to the mercy of a machine going at such a
rate. We will back old Father Thames against the Woolwich Railway for
any sum. We trust that Parliament will, in all railways it may sanction,
limit the speed to _eight or nine miles an hour_, which we entirely
agree with Mr. Sylvester is as great as can be ventured on with safety.”
This passage, which reads so strangely now, may be seen in the
“Quarterly Review” for March, 1825. But still more curious appear now
the reports of the debates in Parliament, and of the evidence taken
before the Parliamentary Committee, in which we find the opinions and
fears of the best informed men of that period, and trace the frantic
efforts of the holders of the “vested interests” to retain them, however
obstructive of the public good.
[Illustration:
FIG. 41.—_Sankey Viaduct._
]
[Illustration:
FIG. 42.—_Rails and Cramp-gauge._
]
When it has been decided to construct a railway between two places, the
laying-out of the line is a subject requiring great consideration and
the highest engineering skill—for the matter is, on account of the great
cost, much more important than the setting-out of a common road. The
idea of a perfect railroad is that of a straight and level line from one
terminus to another; but there are many circumstances which prevent such
an idea from being ever carried into practice. First, it is desirable
that the line should pass through important towns situated near the
route; and then the cost of making the roadway straight and level, in
spite of natural obstacles, would be often so great, that to avoid it
detours and inclines must be submitted to—the inconvenience and the
increased length of road being balanced by the saving in the cost of
construction. It is the business of the engineer who lays out the line
to take all these circumstances into consideration, after he has made a
careful survey of the country through which the line is to pass. The
cost of making railways varies, of course, very much according to the
number and extent of the tunnels, cuttings, embankments, or other works
required. The average cost of each mile of railway in Great Britain may
be stated as about £35,000. The road itself when the rails are laid down
is called _the permanent way_, perhaps originally in distinction to the
temporary tramways laid down by the contractors during the progress of
the works. The permanent way is formed first of _ballast_, which is a
layer of gravel, stone, or other carefully chosen material, about 2 ft.
deep, spread over the roadway. Above the ballast and partly embedded in
it are placed the _sleepers_, which is the name given to the pieces of
timber on which the rails rest. These timbers are usually placed
transversely—that is, across the direction of the rails, in the manner
shown in Fig. 42. This figure also represents the form of rails most
commonly adopted, and exhibits the mode in which they are fastened down
to the sleepers by means of the iron _chairs_, _b_ _c_, the rail being
firmly held in its place by an oak wedge, _d_. These wedges are driven
in while the rails are maintained at precisely the required distance
apart by the implement, _e f_, called a _cramp gauge_, the chairs having
previously been securely attached to the sleepers by bolts or nails. The
double ⟙ form of rail has several important advantages, such as its
capability of being reversed when the upper surface is worn out, and the
readiness with which the ends of the rails can be joined by means of
_fish-plates_. These are shown in Fig. 43, where in a we are supposed to
be looking down on the rails, and in B to be looking at them sideways.
In Fig. 44 we have the rail and fish-plates in section. The holes in the
rails through which the bolts pass are not round but oval, so that a
certain amount of play is permitted to the ends of the rails.
[Illustration:
FIG. 43.—_Fish-plate._
]
It may easily be seen on looking at a line of rails that they are not
laid with the ends quite touching each other, or, at least, they are not
usually in contact. The reason of this is that space must be allowed for
the expansion which takes place when a rise in the temperature occurs.
If the rails are laid down when at the greatest temperature they are
likely to be subject to, they may then be placed in actual contact; but
in cold weather a space will be left by their contraction. For this
reason it is usual when rails are laid to allow a certain interval; thus
rails 20 ft. long laid when the temperature is 70°, are placed with
their ends 1/20th of an inch apart, at 30° 1/10th of an inch apart, and
so on. The neglect of this precaution has sometimes led to damage and
accidents. A certain railway was opened in June, and after an excursion
train had in the morning passed over it, the midday heat so expanded the
iron, that the rails became in some places elevated 2 ft. above the
level, and the sleepers were torn up; so that, in order to admit of the
return of the train, the rails had to be hastily relaid in a kind of
zigzag. In June, 1856, a train was thrown off the metals of the
North-Eastern Railway, in consequence of the rails rising up through
expansion.
[Illustration:
FIG. 44.—_Section of Rails and Fish-plates._
]
The distance between the rails in Great Britain is 4 ft. 8½ in., that
width having been adopted by George Stephenson in the construction of
the earlier lines. Brunel, the engineer of the Great Western, adopted,
however, in the construction of that railway, a gauge of 7 ft., with a
view of obtaining greater speed and power in the engines, steadiness in
the carriages, and increased size of carriages for bulky goods. The
proposal to adopt this gauge gave rise to a memorable dispute among
engineers, often called “The Battle of the Gauges.” It was stated that
any advantages of the broad gauge were more than compensated by its
disadvantages. The want of uniformity in the gauges was soon felt to be
an inconvenience to the public, and a Parliamentary Committee was
appointed to consider the subject. They reported that either gauge
supplied all public requirements, but that the broad gauge involved a
great additional outlay in its construction without any compensating
advantages of economy in working; and, as at that time 2,000 miles of
railway had been constructed on the narrow gauge, whereas only 270 miles
were in existence on the broad gauge, they recommended that future
railways should be made the prevailing width of 56½ in. The Great
Western line had engines, bridges, tunnels, viaducts, &c., on a larger
scale than any other railway in Britain. The difference of gauge was
after a time felt to involve so much inconvenience that lines which
adopted the 7–ft. gauge have since relaid the tracks at the more common
width. At the present day we find the Great Western Railway completely
reconstructed on the narrow gauge system, in order that trains may run
without interruption in connection with other lines.
[Illustration:
FIG. 45.—_Conical Wheels._
]
[Illustration:
FIG. 46.—_Centrifugal Force._
]
The wheels of railway carriages and engines differ from those of
ordinary carriages in being fastened in pairs upon the axles, with which
they revolve (see Fig. 45). The tire of the wheel is conical, the slope
being about 1 in 20; that is, in a wheel 5 in. broad the radius of the
outer edge is ¼ in. less than that of the inner; and the rails are
placed sloping a little inwards. The effect of this conical figure is to
counteract any tendency to roll off the rails; for if a pair of wheels
were shifted a little to one side, the parts of the tires rolling upon
the rails being then of unequal circumference, would cause the wheels to
roll towards the other side. The conical shape produces this kind of
adjustment so well that the flanges do not in general touch the rails.
They act, however, as safeguards in passing over curves and junctions.
In curves the outer line of rails is laid higher than the inner, so that
in passing over them the train leans slightly inwards, in order to
counteract what is called the centrifugal force, to which any body
moving in a curve is subject. This so-called force is merely the result
of that tendency which every moving body has to continue its motion in a
straight line. A very good example of the effect of this may be seen
when a circus horse is going rapidly round the ring. The inclination
inwards is still more perceptible when a rider is standing on the
horse’s back, as shown in Fig. 46. The earth’s attraction of gravity is
pulling the performer straight down, and the centrifugal force would of
itself throw her outwards horizontally. The resultant or combined effect
of both acts is seen in the exact direction in which she is leaning, and
it presses her feet on the horse’s back, the animal itself being under
similar conditions. It is obvious that the amount of centrifugal force,
and therefore of inward slope, will increase with the speed and
sharpness of the curve, and on the railways the rails are placed so that
the slope counteracts the centrifugal force when the train travels at
about the rate of twenty miles per hour.
[Illustration:
FIG. 47.—_Points._
]
A very important part of the mechanism of a railway is the mode of
passing trains from one line of rails to another. Engines and single
carriages are sometimes transferred by means of _turn-tables_, but the
more general plan is by _switches_, which are commonly constructed as
shown in Fig. 47. There are two rails, A and B, tapering to a point and
fixed at the other end, so that they have sufficient freedom to turn
horizontally. A train passing in the direction shown by the arrow would
continue on the main line, if the points are placed as represented; but
if they be moved so that the _long tongue_ is brought into contact with
the rail of the main line, then the train would run on to the side
rails. These _points_ are worked by means of a lever attached to the
rod, C, the lever being either placed near the rails, or in a
_signal-box_, where a man is stationed, whose sole duty it is to attend
to the points and to the signals. The interior of a signal-box near an
important junction or station is shown in Fig. 48, and we see here the
numerous levers for working the points and the signals, each of these
having a connection, by rods or wires, with the corresponding point or
signal-post. The electric telegraph is now an important agent in railway
signalling, and in a signal-box we may see the bells and instruments
which inform the pointsman whether a certain section of the line is
“blocked” or “clear.” The signals now generally used on British railways
are made by the semaphore, which is simply a post from which an arm can
be made to project. When the driver of the train sees the arm projecting
from the left-hand side of the post, it is an intimation to him that he
must stop his train; when the arm is dropped half-way, so as to project
45° from the post, it is meant that he must proceed cautiously; when the
arm is down the line is clear. These signals, of course, are not capable
of being seen at night, when their place is supplied with lamps,
provided with coloured glasses—red and green—and also with an uncoloured
glass. The lamp may have the different glasses on three different sides,
and be turned round so as to present the required colour; or it may be
made to do so without turning, if provided with a frame having red and
green glasses, which can be moved like spectacles in front of it. The
meanings of the various coloured lights and the corresponding semaphore
signals are these:
| White _All right_ Go on.
↿ Green _Caution_ Proceed slowly.
┓ Red _Danger_ Stop.
[Illustration:
FIG. 48.—_Signal-box on the North London Railway._
]
A very clear account of the mode of working railway signals on what is
now called the _block system_, together with a graphic description of a
signal-box, was given in a paper which appeared some years ago in “The
Popular Science Review,” from the pen of Mr. Charles V. Walker, F.R.S.,
the telegraph engineer to the South-Eastern Railway Company, who was the
first to organize an efficient system of electric signalling for
railways. We may remark that the signalling instruments on the
South-Eastern line, and indeed on all the lines at the present day,
address themselves both to the ear and to the eye, for they consist
of—first, bells, on which one, two, or more blows are struck, each
series of blows having its own particular meaning; and, second, of a
kind of miniature signal-post, with arms capable of being moved by
electric currents into positions similar to those of the arm of an
actual signal-post, so that the position of the arms is made always to
indicate the state of the line. One arm of the little signal-post—the
left—is red, and it has reference to _receding_ trains; the other—viz.,
the right—arm is white, and relates to _approaching_ trains. Mr. Walker
thus describes the signalling:
“The ordinary position of the arms of the electro-magnetic telegraph
semaphores will be down; that is to say, when the line is clear of all
trains, and business begins, say in early morning, all the arms will be
down, indicating that no train is moving. When the first train is ready
to start, say from Charing Cross, the signalman will give the proper
bell-signal to Belvidere—two, three, or four blows, according as the
train is for Greenwich, for North Kent, or Mid-Kent, or for the main
line; and the Belvidere man will acknowledge this by one blow on the
bell in reply, and without raising the Charing Cross red or left arm.
This is the signal that the train may go on; and when the train has
passed, so that the Charing Cross man can see the tail lights, he gives
the out signal a second time, which the Belvidere man acknowledges, at
the same time raising the red arm at Charing Cross, behind the train,
and so protecting it until it has passed him at Belvidere, when he
signals to that effect to Charing Cross, at the same time putting down
the red arm there, as an indication that the line is again clear. While
these operations are going on for down trains, others precisely similar,
but in the reverse direction, are going on for up trains.... One and the
same pressure on the key sends a bell signal and raises or depresses the
semaphore arm as the case may require, a single telegraph wire only
being required for the combined system, as for the more simple bell
system.” In one of the signal-boxes on the South-Eastern line, Mr.
Walker states, on a certain day 650 trains or engines were signalled and
all particulars accurately entered in a book, the entries requiring the
writing down of nearly 8,000 figures: an illustration of the amount of
work quietly carried on in a signal-box for the advantage and security
of the travelling public.