June 1894, another great enterprise which had been commenced eight years
before, was inaugurated by the Prince and Princess of Wales as
representatives of Her Majesty the Queen. This was the Tower Bridge,
which not only is one of the most important public works of the century,
but one that presents features of interest and novelty that have never
before been combined in any single structure. The want of an adequate
communication between the shores of the Thames eastward of London Bridge
had long been felt, and was for years a subject of serious consideration
for the Metropolitan authorities. The congested state of the traffic
across London Bridge has often furnished a spectacle for the sight-seer,
and figures are not wanting to show that the number of foot-passengers
alone who daily traverse that bridge, which altogether is only 54 feet
wide, would be equal to the whole population of many considerable
cities: for in 1882 a count showed the daily average of pedestrians to
be 110,525, while the number of vehicles was 22,242. There was much
difference of opinion as to the best method of providing the required
means of communication; but there was an almost universal agreement as
to its position being selected just eastward of the Tower of London. The
map of the districts connected by the Tower Bridge which is given in
Fig. 147_d_, will show a reader who has any acquaintance with London the
suitability of the site. The problem of traversing the river at this
point involved complex conditions as affecting the vehicular traffic and
the navigation, and many different schemes were proposed and examined,
comprised under the three heads of bridges, tunnels and ferries. But a
ferry is always an imperfect means of communication, liable to accidents
and interruptions from fogs, and in severe weather from ice, rendering
the transit impossible for sometimes many days together. A tunnel
beneath the river would, of course, leave the navigation without
impediment, but among its special disadvantages are the great expense of
construction and maintenance, for it has been found that tunnels beneath
waterways are very costly in both respects. Besides, there would have to
be long inclined approaches at each end, and the cost would be
enormously increased by the amount of valuable land these would occupy.
It was indeed proposed that the tunnel should be provided instead with
hydraulic lifts at each end, like those often found in connection with
the sub-ways at railway stations; but such would have to be of
Brobdignagian dimensions, and would daily entail heavy expense. Then, as
regards the bridges, schemes of various kinds were proposed, some even
bridging the whole 850 feet width of the river at a single span, but all
distinguishable by these important characteristics: they either provided
a high level roadway which requires long inclines to reach it, but
permitted lofty-masted ships to pass under it; or, on the other hand,
the roadway was to be made at a low level with a clear headway above the
water of moderate height. While avoiding the inclined approaches, this
plan would either prevent fully rigged vessels passing to the wharves
above the bridge, or some part of the structure would have to open or
swing aside, that the ships might pass through the opening, thus
completely interrupting the pedestrian and vehicular traffic for the
time, with an amount of inconvenience that may be imagined when, as
often happens, twenty large ships or more might pass in the course of a
day, each causing a stoppage of five minutes in the road traffic. Nor
would it be without risks that large vessels could pass through a
comparatively narrow opening in a strong tide-way. Plans for sub-ways,
for high level roadways and for low level roadways, were examined by
Parliamentary Committees when powers to construct the works were
successively applied for by the Metropolitan authorities, and much
valuable evidence having been given, such objectionable features of each
scheme as have been already referred to were duly noted. At length in
1878, Mr. Horace Jones, the late architect to the City of London, in a
report on the various projects, suggested the general plan on which the
present bridge is built, and this having been approved of by the Common
Council, steps were taken to obtain Parliamentary powers to raise the
necessary capital and to proceed with the works; but, for various
reasons, it was not until 1885 that the Act authorising the undertaking
was passed. In the meantime Mr. John Wolfe Barry was appointed engineer
of the structure, while Mr. Jones was to superintend the architectural
details; but after having received the honour of knighthood in 1885, he
died in the same year; and Mr. Barry, reconsidering the joint design,
introduced some new features and somewhat modified the architectural
expression of the structure. One striking point of originality about the
Tower Bridge is that while it is essentially an iron and steel
construction as much as the Forth Bridge, the heavy stiff metal-work is
encased in masonry of elegant and appropriate architectural design, by
which the general desire that the bridge should harmonize so far as
might be, with the ancient historical fortress it adjoins, has been
happily realised. Then again, by the ingenious engineering, the public
have the advantage of a low level roadway, while the largest vessels may
pass freely through a wide space without risk. These apparently
incompatible advantages have been obtained by the adoption of what is
the _bascule_ principle on a hitherto unattempted scale. _Bascule_ is a
French engineering term, which is probably less familiar to most of our
readers than the thing itself. It is applied to the platform of a
draw-bridge which turns as the lid of a box does on its hinges, to
afford a passage over the stream or moat when it is horizontal, and when
drawn up vertically denies such passage. Smaller _bascule_ bridges on
exactly the same plan as in the Tower Bridge may often be seen in places
having docks or canals, such as Hull, &c. In these a flap or platform is
let down from each side from the vertical position, in which the
water-way is open until the free edges meet together to form the
roadway. These platforms turn on horizontal pivots, and are
counterpoised by loads of stone or metal, so that they are without
difficulty raised and lowered by a winch or handle that turns a cogged
pinion engaging the teeth of a large quadrant.
[Illustration:
PLATE XIV.
THE TOWER BRIDGE IN COURSE OF CONSTRUCTION.
]
[Illustration:
“THE ENGINEER” SWAIN ENG.
FIG. 147_d_.—_Map of the Tower Bridge and its Approaches._
]
The following general description of the Tower Bridge is mainly
abstracted from a very full and excellent account of it drawn up in 1894
by Mr. J. E. Tuit, engineer to Sir W. Arrol & Co., the contractors, in
which are embraced the whole of the technical details of the structure.
The map, Fig. 147_d_, shows the site of the bridge and its approaches,
of which the northern one begins close to the mint and passes along the
east side of the Tower of London to the northern abutment. This approach
is formed of a series of brick arches, and is nearly 1,000 feet long and
35 feet wide in the roadway, with a footpath 12½ feet wide on either
side of it. The incline is only a rise of 1 in 60, but the southern
approach is slightly steeper, namely, 1 in 40 leaving the street level
at Tooley Street. At each abutment there are also stairs connecting the
banks of the river with the roadway of the bridge. The width of the
river between the two abutments is 880 feet, and this is divided, as
shown in Fig. 147_e_, into two side spans, each 270 feet wide, and one
central span of 200 feet clear, making together 740 feet, the river
piers, each of which is 70 feet wide, completing the total span. The
clear headway above high water, when the _bascules_ or leaves are down,
is, in the middle span, 29½ feet in the centre, but only 15 feet at the
ends; but when the leaves are raised for ships to pass, it is about 143
feet. The headway at the shore sides of the piers is 27 feet, but this
is lessened to 23 feet and 20 feet at the north and south abutments
respectively. The roadway and footpaths are continued along the side
spans of the same width as on the approaches, but over the central span
the road is 32 feet, and each footway 8½ feet wide. The river piers are
said to be the largest in the world of the same kind, and their great
area was necessitated by the nature of the London clay on which they
rest, which was found incapable of bearing a load much exceeding four
tons per square foot without some risk of undue settlement.
The part of the piers below the bed of the river is formed of concrete,
while the upper part is brickwork, set in cement and faced with Cornish
granite. Upon each of the river piers rest four octagonal columns, built
up of flat steel plates, connected together at their edges by splayed
angle-bars. The columns are 120 feet high, and 5½ feet in diameter;
those on each pier are securely braced together, at certain stages also
by plate girders, 6 feet deep, to form a floor or landing, and the tops
of the columns are similarly joined together. At the height of 143 feet
above high water there are two footways, each 12 feet wide and 230 feet
long, carried on girders over the central span, and supported by the
columns on each pier. It must be noted that all the roadway, and, in
fact, all the practical and useful structure of the bridge, depend upon
the steel-work alone, which is supported mainly by the eight octagonal
columns just mentioned. The architectural features, which so
appropriately clothe all the steel columns, are added for æsthetic
considerations, and their masonry takes no part in bearing the weights
and strains of the structure. Indeed, the stone-work of the towers is
carefully separated from the columns, which were covered with canvas
while the masonry was built round them, and spaces were left at every
point where compression of the steel-work would bring weight upon the
stone-work. This investment of the metal-work by beautiful architecture
is, as already mentioned, one of the most original features of the Tower
Bridge. The view of the work in progress, as given in Plate VIII., which
is one of the many beautiful illustrations in Mr. Tuit’s book, will give
the reader an opportunity of judging how much the structure gains in
sightliness by the addition of the architectural features. Two hydraulic
lifts are placed in each tower to convey pedestrians to and from the
higher level footways, when the moving parts of the bridge are open, and
stairs also are provided for the same purpose for those who prefer them
to using the lifts.
[Illustration:
FIG. 147_e._—_The Tower Bridge._
]
Length of Bridge with its approaches 2680 feet.
Length of Northern approach 1000 feet.
Length of Southern approach 800 feet.
Width between N. and S. abutments 830 feet.
Width of central span 200 feet.
Width of side spans, each 270 feet.
Depth of River at high water under central span 33½ feet.
Depth of River at lowest tides under central span 12 feet.
Clear headway at high water when the leaves are down (varies 20 to 29½
from one part of the bridge to another) feet.
Clear headway in centre span at high water with the leaves 143 feet.
raised
The side spans are really suspension bridges, but the chains have only
two links, connected at the lowest point by a pin 2½ feet in diameter,
while their higher ends are supported on the columns of the piers, and
on similar but shorter columns on the abutments. The horizontal pulls of
the chains on the piers are made to balance each other by connecting the
chains to tie bars stretching across the central span, and the landward
ends of the chains, after passing over the lower columns of the
abutments, are securely anchored in enormous masses of concrete.
Each of the opening parts, or _bascules_, or leaves, as they may be
called, consists of four girders 18½ feet apart, rigidly braced
together, and connected at the pier end with a great shaft, 48 feet long
and 1 foot 9 inches in diameter, which turns in massive bearings,
resting upon four fixed girders. The leaf is counterbalanced on the
shore side of the pivot shaft by 350 tons of lead and iron; the short
leverage of the centre-weight and small space available for it required
the greater part of this weight to be of lead, rather than of the less
expensive metal. The pivot shaft passes through the centre of gravity of
the whole, so that, although the total weight is nearly 1,200 tons, no
very great power is required to set it in motion, as the pivot shaft
rests on rollers to diminish the friction. The power for moving the leaf
is applied to toothed quadrants of 42 feet radius, of which two are
fixed to the outside girders of each leaf, and are geared into cogs
moved by eight large hydraulic engines, with six accumulators, into
which water is pumped by two engines, each of 360 horse-power.
The total length of the bridge, including the approaches, is just half a
mile, and the height of the towers from the foundations is 293 feet, so
that if one of them were placed beside St. Paul’s Cathedral, it would
compare with it in height as shown in the sketch, Fig. 147_f_.
[Illustration:
FIG. 147_f_.—_Sketch._
]
_THE GREAT BROOKLYN BRIDGE._
The Clifton Bridge at Niagara Falls, which for a time had the
distinction of being the longest in span of any suspension bridge in the
world, has been fully described in previous pages; but more recently
this bridge has been surpassed in span, and in all other respects, by a
structure that immediately connects two of the most populous localities
in the United States of America. The Island of Manhattan, which is
occupied by the city of New York proper, has a population of nearly two
millions, and a strait on its eastern side, connecting Long Island Sound
with New York Harbour, alone divides it from the other great seats of
population, called respectively Long Island City and Brooklyn. This
channel is about ten miles long, and of a varying width, which may
average three-quarters of a mile. There are many ferries between the
opposite shores, and the waters are busy with steamers, sailing-boats,
tugs, and craft of all kinds, engaged either in traffic with ports near
at hand, or in trade with distant lands. At the southern end of this
strait, near the point of its junction with New York Bay, is the
narrowest part of its course, and it is here that it is crossed by the
magnificent suspension bridge, known indifferently as the East River
Bridge, or Brooklyn Bridge, which provides land communication between
New York, with its population of two millions, and Brooklyn, the fourth
city of the States in point of size, with inhabitants numbering about
one million. Brooklyn is largely a residential place for persons whose
daily business is in New York. It has wide, well-planned streets, many
shaded by the luxuriant foliage of double rows of trees, and possesses
parks, public buildings, institutes, churches, etc., on a scale
commensurate with its importance.
The central span of Brooklyn Bridge, from tower to tower, is 1,595 feet,
and each shore part, extending from the tower to the anchorage of the
cables, is 930 feet span, while the two approaches beyond the anchorage
together add 2,534 feet to the total length, which is 5,989 feet, or
considerably over a mile. The centre span, it will be observed, is much
greater than that of the Niagara Falls Clifton Bridge, which was less
than one quarter of a mile, whereas the Brooklyn Bridge span extends to
something approaching one-third of a mile, or, more exactly, a few yards
longer than three-tenths. The width of the Brooklyn is another one of
its remarkable features, for this is no less than 85 feet, and includes
two roadways for ordinary vehicles, and two tramway tracks, on which the
carriages are moved by an endless cable, worked by a stationary engine
on the Brooklyn side. There is also a footpath, 13 feet wide, for
pedestrians. In this structure, as in many other suspension bridges,
advantage has been taken of the great tenacity of steel wire as compared
with iron bars. But here the wires are not twisted in strands like
ropes, but are laid straight together, and bound into a cylindrical
form, each wire being 3,572 feet long, and extending from end to end of
the cables, which are four in number, each calculated to bear a strain
of 12,200 tons. The number of wires in each cable is very great, for
instead of about the thousand of which the stranded wire cables usually
consist, there are 5,296 steel wires wrapped closely round, and forming
a cylinder 15¾ inches in diameter. Each wire is galvanised, that is,
coated with zinc, and then coated with oil. The towers over which the
cables pass are of masonry, and rise to 272 feet above high-water; their
dimensions at the water level are 140 feet by 50 feet, which offsets
diminish until at the top they are 120 feet by 40 feet. At the anchor
structures, the cables enter the masonry at nearly 80 feet above
high-water, and pass 28 feet into the stonework for connection with the
anchor chains. The anchorages are masses of masonry, measuring at the
base 129 feet by 119 feet, and at the top 117 feet by 104 feet, with a
height of 89 feet in front and 85 feet in the rear. The weight of each
anchor-plate is 23 tons. The roadway of the bridge is suspended from the
cables above the buildings and streets between the towers and the
anchorages. The approaches, on the Brooklyn side 971 feet, on the New
York side 1,563 feet, are carried on stonework arches, which are
utilised as warehouses, but where these approaches cross streets, iron
bridges are thrown over. The clear headway between the centre of the
roadway over the river at high-water is 135 feet, so that there is no
obstruction to navigation, and the headway at the towers is 119 feet, so
that the roadway rises towards the centre about 3 feet 3 inches in 100
feet. The two towers comprise more than 85,000 cubic yards of masonry,
and for various purposes 13,670 tons of concrete were used. The work was
commenced in January, 1870, and the first wire was carried across on
29th May, 1877. The bridge was opened to the public on the 24th of May,
1883, and the tramway four months later. The bridge was made free for
pedestrians in 1891, and in 1894 the tram-car fares were reduced to five
cents (2½_d._) for two journeys. In that year, 41,927,122 passengers
were carried on the cars. The average number of persons daily crossing
the bridge is estimated at about 115,000, although on one day (11th
Feb., 1895) as many as 225,645 passengers have been carried on the cars.
The cost of the work connected with this great bridge was $15,000,000
(£3,125,000).
In relation to the subject of wide-spanning bridges, the erection has
been contemplated of structures which would surpass in magnitude and
boldness any of those yet named. Thus, in 1894, the New York Chamber of
Commerce proposed to throw across the River Hudson, which washes the
western side of New York, a bridge with a clear span of 3,200 feet
(six-tenths of a mile), and 500 feet clear height; and the project was
declared by an eminent and experienced engineer to be quite feasible.
[Illustration:
PLATE XV.
THE BROOKLYN BRIDGE.
]
[Illustration:
FIG. 148.—_Newspaper Printing-Room, with Walter Machines._
]
PRINTING MACHINES.
A volume might be filled with descriptions of the machines which in
every department of industry have taken the place of slow and laborious
manual labour. But if even we selected only such machines as from the
beautiful mechanical principles involved in their action, or from their
effects in cheapening for everybody the necessaries and comforts of
life, might be considered of universal interest, the limits of the space
we can afford for this class of inventions would be far exceeded. The
machines for spinning, for weaving fabrics, for preparing articles of
food, are in themselves worthy of attention; then there is a little
machine which in almost every household has superseded one of the most
primitive kinds of hand-work, and that is the sewing machine. But all
these we must pass over, and confine our descriptions of special
machines to a class in which the interest is of a still more general and
higher character, since their effect in promoting the intellectual
progress of mankind is universally acknowledged. We need hardly say that
we allude to Printing Presses, and if we add a few lines on printing
machines other than those which have given us cheap literature, it is
because these other machines also have contributed to the general
culture by giving us cheap decorative art, and in their general
principles they are so much akin to the former that but little
additional description is necessary.
_LETTERPRESS PRINTING._
The manner in which the youthful assistants of printers came to receive
their technical appellation of “devils” has been the subject of many
ingenious explanations. One of these is to the effect that the earlier
productions of the press, having imitated the manuscript characters, the
uninitiated supposed the impressions were produced by hand-copying, and
in consequence of their rapid production and exact conformity with each
other, it was thought that some diabolical agency must have been
invoked. Another story relates that one of Caxton’s first assistants was
a negro boy, who of course soon became identified in the popular mind
with an imp from the nether world. A very innocent explanation is put
forward in another tale, relating that one of the first English printers
had in his employment a boy of the name of De Ville, or Deville, which
name was soon corrupted into the now familiar title, and became the
inheritance of this youth’s successors in the craft. Perhaps a more
probable and natural explanation might be found in the personal
appearance which the apprentices must have presented, with hands, and no
doubt faces also, smeared over with the black ink which it was their
duty to manipulate. For the ink was formerly always laid upon large
round pads or balls of leather, stuffed with wool. When these balls,
Fig. 149, which were, perhaps, about 12 in. in diameter, had received a
charge of ink, the apprentice dabbed the one against the other, working
them with a twisting motion, and after having obtained a uniform
distribution of the ink on their surfaces with many dexterous
flourishes, he applied them to the face of the types with both hands,
until all the letters were completely and evenly charged. The operation
was very troublesome, and much practice was required before the
necessary skill was obtained, while it was always a most difficult
matter to keep the balls in good working condition.
[Illustration:
FIG. 149.—_Inking Balls._
]
[Illustration:
FIG. 150.—_Inking Roller._
]
The first important step towards the possibility of a printing machine
was made, when for these inking balls was substituted a cylindrical
roller, mounted on handles, Fig. 150. The body of the roller is of wood,
but it is thickly coated with a composition which unites the qualities
of elasticity, softness, and readiness to take up the ink and distribute
it evenly over the types. The materials used for this composition are
chiefly glue and treacle, and sometimes also tar, isinglass, or other
substances. Glycerine and various other materials have also been
proposed as suitable ingredients for these composition rollers, but it
is doubtful whether the original compound is not as efficacious as any
yet tried. The composition is not unlike india-rubber in its appearance
and some of its properties. Fig. 150 represents equally the mode in
which the roller is applied to the type in hand presses, and that in
which it is charged with ink, by being moved backwards and forwards over
a smooth table upon which the ink has been spread.
From the time of the first appearance of printing presses in Europe down
to almost the beginning of the present century, a period of 350 years,
no improvement in the construction appears to have been attempted. They
were simply wooden presses with screws, on exactly the same plan as the
cheese-presses of the period. Earl Stanhope first, in 1798, made a press
entirely of iron, and he provided it with an excellent combination of
levers, so that the “platen,” or flat plate which overlies the paper and
receives the pressure, is forced down with great power just when the
paper comes in contact with the types. Such presses are capable of
turning out about 250 impressions per hour, and it should be noted that
the very finest book printing is still done by presses upon this
principle. One reason is that in such cases, where it is desired to
print with the greatest clearness and depth of colour, the ink employed
is much thicker, or stiffer, and requires more thorough distribution and
application to the type than a machine can effect. Stanhope’s press was
not of a kind to meet the desire for rapid production, to which the
increasing importance of newspapers gave rise. The first practical
success in this direction was achieved by König, who, in 1814, set up
for Mr. Walter, the proprietor of the “Times,” two machines, by which
that newspaper was printed at the rate of 1,100 impressions per hour,
the machinery being driven by steam power.
The “Times” of the 28th November, 1814, in the following words made its
readers acquainted with the fact that they had in their hands for the
first time a newspaper printed by steam power:
“Our journal of this day presents to the public the practical result of
the greatest improvement connected with printing since the discovery of
the art itself. The reader of this paragraph now holds in his hand one
of many thousand impressions of ‘The Times’ newspaper, which were taken
off by a mechanical apparatus. A system of machinery almost organic has
been devised and arranged, which, while it relieves the human frame of
its most laborious efforts in printing, far exceeds all human powers in
rapidity and dispatch. That the magnitude of the invention may be justly
appreciated by its effects, we shall inform the public that after the
letters are placed by the compositors, and enclosed in what is called
the ‘form,’ little more remains for man to do than to attend upon and
watch this unconscious agent in its operations. The machine is then
merely supplied with paper, itself places the form, inks it, adjusts the
paper to the form newly inked, stamps the sheet, and gives it forth to
the hands of the attendant, at the same time withdrawing the form for a
fresh coat of ink, which itself again distributes, to meet the ensuing
sheet now advancing for impression, and the whole of these complicated
acts is performed with such a velocity and simultaneousness of movement
that no less than 1,100 sheets are impressed in one hour. That the
completion of an invention of this kind, not the effect of chance, but
the result of mechanical combinations, methodically arranged in the mind
of the artist, should be attended with many obstructions and much delay
may be readily admitted. Our share in this event has, indeed, only been
the application of the discovery, under an agreement with the patentees,
to our own particular business; yet few can conceive, even with this
limited interest, the various disappointments and deep anxiety to which
we have for a long course of time been subjected. Of the person who made
the discovery we have little to add. Sir Christopher Wren’s noblest
monument is to be found in the building which he erected: so is the best
tribute of praise which we are capable of offering to the inventor of
the printing machine comprised in the preceding description, which we
have feebly sketched, of the powers and utility of his invention. It
must suffice to say further, that he is a Saxon by birth, that his name
is König, and that the invention has been executed under the direction
of his friend and countryman, Bauer.”
[Illustration:
FIG. 151.—_Diagram of Cowper and Applegath’s Single Machine._
]