Anecdotes of Painters, Engravers, Sculptors and Architects and Curiosities of Art (Vol. 3 of 3) - S. Spooner (ap literature book list .TXT) 📗

commenced by closing the valves in the pontoons at low

water; as the tide rises, the pontoons will begin to float, and shortly

afterwards to bear the weight of the tube, which will at last be raised

by them entirely off its temporary supporting piers; about an hour and a

half before high water, the current running about four miles an hour, it

will be dragged out into the middle of the stream, by powerful capstans

and hawsers, reaching from the pontoons at each end, to the opposite

shore. In order to guide it into its place with the greatest possible

certainty, three large hawsers will be laid down the stream, one end of

two of them being made fast to the towers (piers) between which the tube

is intended to rest, and the other to strong fixed points on the two

shores, near to and opposite the further end of the tube platforms; in

their course, they will pass over and rest upon the pontoons, being

taken through 'cable-stoppers' which are contrivances for embracing and

gripping the hawser extended across the stream, and thereby retarding,

or if necessary entirely destroying, the speed induced by the current."

 

 

 

 

RAISING THE TUBES

 

 

The tubes of the Britannia bridge were raised by means of three

hydraulic presses of the most prodigious size, strength, weight, and

power; two of which were placed in the Britannia pier, above the points

where the tubes rest, and the other alternately on the Anglesea and

Carnarvon piers.

 

In order that all who read these pages may understand this curious

operation, it is necessary to describe the principle of the hydraulic

press. If a tube be screwed into a cask or vessel filled with water, and

then water poured into the tube, the pressure on the bottom and sides of

the vessel will not be the contents of the vessel and tube, but that of

a column of water equal to the length of the tube and the depth of the

vessel. This law of pressure in fluids is rendered very striking in the

experiment of bursting a strong cask by the action of a few ounces of

water. This law, so extraordinary and startling of belief to those who

do not understand the reasoning upon which it is founded, has been

called the _Hydrostatic paradox_, though there is nothing in reality

more paradoxical in it, than that one pound at the long end of a lever,

should balance ten pounds at the short end. This principle has been

applied to the construction of the Hydrostatic or Hydraulic press,

whose power is only limited by the strength of the materials of which it

is made. Thus, with a hydraulic press no larger than a common tea-pot, a

bar of iron may be cut as easily as a slip of pasteboard. The exertion

of a single man, with a short lever, will produce a pressure of 1500

atmospheres, or 22,500 pounds on every square inch of surface inside the

cylinder. By means of hydraulic presses, ships of a thousand tons

burthen, with cargo on board, are lifted out of the water for repairs,

and the heaviest bodies raised and moved, without any other expense of

human labor beyond the management of the engine.

 

The tubes on the Anglesea side were raised first. The presses in the

Britannia tower were each capable of raising a weight of 1250 tons; that

in the Anglesea tower, larger than the others, 1800 tons, or the whole

weight of the tube. These presses were worked by two steam engines of 40

horse power each, which forced the water into the cylinders, through a

tube half an inch in diameter. These steam engines were placed in the

Britannia and Anglesea piers. The press in the Anglesea pier is thus

described, the others being constructed in the same manner. The

hydraulic press stands on massive beams of wrought iron plates

constructed on the principle of the arch, placed in the tower above the

points where the tubes rest. The press consists of a huge cylinder, 9

feet 2 inches in length, 3 feet 6 inches outside diameter, and the ram 1

foot 8 inches in diameter, making the sides and bottom of the cylinder

11 inches thick; it was calculated that it would resist a pressure of

8000 or 9000 pounds to the square inch. The ram or piston was attached

to an exceedingly thick and heavy beam of cast iron, called the

cross-head, strengthened with bars of wrought iron. To the cross-head

were attached the huge chains that descended to the tubes far below, to

which they were secured, so that, as the ram was forced up 6 feet at

each stroke, the tube was raised the same distance. "The power of the

press is exerted on the tube by aid of chains, the links of which are 6

feet in length, bolted together in sets of eight or nine links

alternately.--The ram raises the cross-head 6 feet at each stroke, and

with it the tube, when that height is attained, a lower set of chains on

the beams grip the next set of links, and thus prevent them from

slipping down, whilst the clamps on the cross-heads are unscrewed, the

upper links taken off, and the ram and cross-head lowered to take

another stroke." To guard against all chances of injury to the tubes in

case of accident to the machinery, a contrivance was adopted by which

the tubes were followed up with wedges. The importance of this

precaution was fully proved on the very first attempt to raise the tube

on the Anglesea side, when the huge cylinder broke, almost at the

commencement of the operations. The following is the engineer's

interesting report of the accident:

 

"On Friday last (August 17, 1849), at a quarter to twelve o'clock, we

commenced lifting the tube at the Anglesea end, intending to raise it

six feet, and afterwards to have raised the opposite end the same

height.

 

"The tube rose steadily to the height of two feet six inches, being

closely followed up by inch wooden boards packed beneath it, when

suddenly, and without any warning, the bottom of the hydraulic press

gave way, separating completely from the body of the press.

 

"The ram, cross-head, and chains descended violently on the press, with

a tremendous noise, the tube sinking down upon the wooden packing

beneath it. The bottom of the press, weighing nearly two tons and a

half, fell on the top of the tube, a depth of eighty feet.

 

"A sailor, named Owen Parry, was ascending a rope ladder at the time,

from the top of the tube into the tower; the broken piece of press in

its descent struck the ladder and shook him off; he fell on to the tube,

a height of fifty feet, receiving a contusion of the skull, and other

injuries, of so serious a nature that he died the same evening. He was

not engaged in the raising, and had only chosen to cross the tube, as

being the nearest road from one tower to the other. An inquest was held

on the following day, and a verdict of accidental death returned. No one

actually engaged in the operation was injured, although Mr. Edwin

Clark, who was superintending the operation, on the top of the

cross-head, and his brother, Mr. L. Clark, who was standing beneath it,

had both a very narrow escape.

 

"The tube is not at all injured, but some portions of the cast iron

lifting frames are broken, and require repairing; some weeks must elapse

before a new cylinder is made, and the operation continued."

 

Sir Francis Head, when he saw one of the tubes raised, and in its place,

observed, "It seemed surprising to us that by any arrangement of

materials, it could possibly be made strong enough to support even

itself,--much less heavily laden trains of passengers and goods, flying

through it, and actually passing each other in the air at railway speed.

And the more we called reason and reflection to our assistance, the more

incomprehensible did the mystery practically appear; for the plate iron

of which the aërial gallery is composed is literally _not so thick_ as

the lid, sides, and bottom which, by heartless contract, are _required_

for an elm coffin 6½ feet long, 2¼ wide, and 2 deep, of strength

merely sufficient to carry the corpse of an emaciated pauper from the

workhouse to his grave! The covering of this iron passage, 1841 feet in

length, is literally not thicker than the hide of an elephant; lastly,

it is scarcely thicker than the bark of the good old English oak,--and

if this noble sovereign, notwithstanding 'the heart' and interior

substance of which it boasts, is, even in the well-protected park in

which it has been born and bred, often prostrated by the storm, how

difficult is it to conceive that an attenuated aërial hollow beam, no

thicker than its mere rind, should, by human science, be constructed

strong enough to withstand, besides the weights rushing through it, the

natural gales and artificial squalls of wind to which, throughout its

entire length, and at its fearful height, it is permanently to be

exposed."

 

Notwithstanding these "incomprehensible" speculations, the tubes are

abundantly strong to sustain the pressure of the heaviest trains, even

were they to stand still in the middle of the bridge. It is calculated

that each tube, in its weakest part, would sustain a pressure of four or

five thousand tons, "support a line of battle ship, with all her

munitions and stores on board," and "bear a line of locomotives covering

the entire bridge." The bridge was completed, and the first train passed

through it March 5th, 1850. The total cost of this gigantic structure

was only £601,865.

 

 

 

 

GLORY OF ANCIENT ROME.

 

 

Ancient Rome was built upon seven hills, which are now scarcely

discoverable on account of the vast quantities of rubbish with which the

valleys are filled. Pliny estimates the circumference of the city in his

time at 13,000 paces (which nearly agrees with modern measurements), and

the population at 3,000,000. Rome was filled with magnificent public

edifices, temples, theatres, amphitheatres, circuses, naumachiæ,

porticos, basilicæ, baths, gardens, triumphal arches, columns, sewers,

aqueducts, sepulchres, public and private palaces, etc.

 

In the time of the Cæsars, fourteen magnificent aqueducts, supported by

immense arches, conducted whole rivers into Rome, from a distance of

many miles, and supplied one hundred and fifty public fountains, one

hundred and eighteen large public baths, the artificial seas in which

naval combats were represented in the Colosseum, and the golden palace

of Nero, besides the water necessary to supply the daily use of the

inhabitants. One hundred thousand marble and bronze statues ornamented

the public squares, the temples, the streets, and the houses of the

nobility: ninety colossal statues raised on pedestals; and forty-eight

Egyptian obelisks of red granite, some of the largest size, also adorned

the city.

 

Such was ancient Rome, "the Eternal City." Although visited for more

than a thousand years by various calamities, she is still the most

majestic of cities; the charm of beauty, dignity, and grandeur still

lingers around the ruins of ancient, as well as the splendid structures

of modern Rome, and brilliant recollections of every age are connected

with the monuments which the passing traveler meets at every step.

 

 

 

 

THE CAPITOL.

 

 

The Capitol or Citadel of ancient Rome stood on the Capitoline hill, the

smallest of the seven hills of Rome, called the _Saturnine_ and

_Tarpeian rock_. It was begun B.C. 614, by Tarquinius Priscus, but was

not completed till after the expulsion of the kings. After being thrice

destroyed by fire and civil commotion, it was rebuilt by Domitian, who

instituted there the Capitoline games. Dionysius says the temple, with

the exterior palaces, was 200 feet long, and 185 broad. The whole

building consisted of three temples, which were dedicated to Jupiter,

Juno, and Minerva, and separated from one another by walls. In the wide

portico, triumphal banquets were given to the people. The statue of

Jupiter, in the Capitol, represented the god sitting on a throne of

ivory and gold, and consisted in the earliest times of clay painted red;

under Trajan, it was formed of gold. The roof of the temple was made of

bronze; it was gilded by Q. Catulus. The doors were of the same metal.

Splendor and expense were profusely lavished upon the whole edifice. The

gilding alone cost 12,000 talents (about $12,000,000), for which reason

the Romans called it the _Golden Capitol_. On the pediment stood a

chariot drawn by four horses, at first of clay, and afterwards of brass

gilded. The temple itself contained an immense quantity of the most

magnificent presents. The most important state papers, and particularly

the Sibylline books were preserved in it. A few pillars and some ruins

are all that now remain of the magnificent temple of Jupiter

Capitolinus. Its site is mostly occupied by the church of the

Franciscans, and partly by the modern capitol called the _Campidoglio_,

which was erected after the design of