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Scientific American Supplement, No. 841, February 13, 1892 online

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to the fort as the range of its guns and the nature of the ground will
permit. From this line the troops rush forward at night and open the
trenches, beginning with what is called the first parallel, which
should be so laid out as to envelop those parts of the fort which are
to be made the special objects of attack. From this first parallel a
number of zigzag trenches are started toward the fort and at proper
intervals other parallels, batteries, and magazines are built; this
method of approach being continued until the besieged fort is reached,
or until such batteries can be brought to bear upon it as to breech
the walls and allow the attacking troops to make an assault.

During these operations of course many precautions must be observed,
both by the attacking and defending force, to annoy each other and to
prevent surprise, and the work is mostly carried on under cover of the
earth thrown from the trenches. These operations were supposed to
occupy, under normal conditions, about forty-one days, or rather
nights, as most of the work is done after dark, at the end of which
time the fort should be reduced to such a condition that its
commander, having exhausted all means of defense, would be justified
in considering terms of surrender.

The _Theoretical Journal_ of the siege prescribes just what is to be
done each day by both attack and defense up to the final catastrophe,
and this somewhat discouraging outlook for the defenders was forcibly
illustrated by the late Captain Derby, better known by the reading
public as "John Phoenix," who, when a cadet, was called upon by
Professor Mahan to explain how he would defend a fort, mounting a
certain number of guns and garrisoned by a certain number of men, if
besieged by an army of another assumed strength in men and guns,
replied:

"I would immediately evacuate the fort and then besiege it and capture
it again in forty-one days."

Of course the fallacy of this reasoning was in the fact that the
besieging army is generally supposed to be four or five times as large
as the garrison of the fort; the primary object of forts being to
enable a small force to hold a position, at least for a time, against
a much larger force of the enemy.

Sieges have changed with the development of engines of war, from the
rude and muscular efforts of personal prowess like that described in
Ivanhoe, where the Black Knight cuts his way through the barriers with
his battle axe, to such sieges as those at Vicksburg, Petersburg, and
Plevna, where the individual counted for very little, and the results
depended upon the combined efforts of large numbers of men and
systematic siege operations. It should also be noticed that modern
sieges are not necessarily hampered by the rules laid down in text
books, but vary from them according to circumstances.

For example, many sieges have been carried to successful issues
without completely investing or surrounding the fortress. This was the
case at Petersburg, where General Lee was entirely free to move out,
or receive supplies and re-enforcements up to the very last stages of
the siege. In other cases, as at Fort Pulaski, Sumter, and Macon, the
breeching batteries were established at very much greater distances
than ever before attempted, and the preliminary siege operations were
very much abbreviated and some of them omitted altogether. This is not
an argument against having well defined rules and principles, but it
shows that the engineer must be prepared to cut loose from old rules
and customs whenever the changed state of circumstances requires
different treatment.


MILITARY BRIDGES.

In the movement of armies, especially on long marches in the enemy's
country, one of the greatest difficulties to be overcome is the
crossing of streams, and this is usually done by means of portable
bridges. These may be built of light trestles with adjustable legs to
suit the different depths, or of wooden or canvas boats supporting a
light roadway wide enough for a single line of ordinary wagons or
artillery carriages. The materials for these bridges, which are known
as Ponton Bridges, are loaded upon wagons and accompany the army on
its marches, and when required for use the bridge is rapidly put
together, piece by piece, in accordance with fixed rules, which
constitute, in fact, a regular drill. The wooden boats are quite heavy
and are used for heavy traffic, but for light work, as, for example,
to accompany the rapid movements of the cavalry, boats made of heavy
canvas, stretched upon light wooden frames, that are put together on
the spot, are used.

During Gen. Sherman's memorable Georgia campaign and march to the sea,
over three miles of Ponton bridges were built in crossing the numerous
streams met with, and nearly two miles of trestle bridges. In Gen.
Grant's Wilderness campaign the engineers built not less than
thirty-eight bridges between the Rappahannock and the James Rivers,
these bridges aggregating over 6,600 feet in length. Under favorable
circumstances such bridges can be built at the rate of 200 to 300 feet
per hour, and they can be taken up at a still more rapid rate. When
there is no bridge train at hand the engineer is obliged to use such
improvised materials as he can get; buildings are torn down to get
plank and trees are cut to make the frame. Sometimes single stringers
will answer, but if a greater length of bridge is required it may be
supported on piles or trestles, or in deep water on rafts of logs or
casks. But the heavy traffic of armies, operating at some distance
from their bases, must be transported by rail, and the building of
railway bridges or rebuilding those destroyed by the enemy is an
important duty of the engineer. On the Potomac Creek, in Virginia, a
trestle bridge 80 feet high and 400 feet long was built in nine
working days, from timber out of the neighborhood. Another bridge
across the Etowah River, in Georgia, was built in Gen. Sherman's
campaign, and a similar bridge was also built over the Chattahoochee.


SURVEYS AND EXPLORATIONS.

For more than half a century before the building of the great Pacific
railways, engineer officers were engaged in making surveys and
explorations in the great unknown country west of the Mississippi
River, and the final map of that country was literally covered with a
network of trails made by them. Several of these officers lost their
lives in such expeditions, while others lived to become more famous as
commanders during the great rebellion. Generals Kearney, J.E.
Johnston, Pope, Warren, Fremont and Parke, and Colonels Long, Bache,
Emory, Whipple, Woodruff and Simpson, Captains Warner, Stansbury,
Gunnison and many other officers, generally in their younger days,
contributed their quota to the geographical knowledge of the country,
and made possible the wonderful network of railways guarded by
military posts that has followed their footsteps. Their reports fill
twelve large quarto volumes.


BOUNDARY AND LAKE SURVEYS.

The astronomical location of the boundaries of the several States and
Territories, as well as of the United States, is a duty frequently
required of the engineer officer, and such a survey between this
country and Mexico is now in progress. The entire line of the 49th
parallel of latitude from the Lake of the Woods to the Pacific Ocean,
which forms our northern boundary, was located a few years ago by a
joint commission of English and United States engineers, and monuments
were established at short intervals over its entire length.

A careful geodetic and hydrographic survey of the Great Northern
Lakes, including every harbor upon them and the rivers connecting
them, was carried on for many years and was finally completed some ten
years ago. Maps and charts of these surveys are published from time to
time for use of pilots navigating these waters.

Not only are the duties of the military engineer similar in many
respects to those of the civil engineer, but there are many instances
in which the duties of one branch of the profession have been
performed by members of the other branch, quite as efficiently as
though they had been performed by engineers specially educated for the
purpose. During the late civil war there were many illustrations of
this, all showing that an ingenious engineer can readily adapt himself
to circumstances entirely different from those to which he has been
accustomed. A very good example of this occurred in the Red River
expedition of General Banks and Admiral Porter. In that memorable but
disastrous campaign an army accompanied by a fleet of transports and
light draught gunboats, sometimes called "tin clads" because some
parts of them were covered with boiler plate to stop the bullets of
the enemy, ascended the Red River in Louisiana; but the advance having
been checked and a retreat commenced, it was found that the river had
fallen to such a low state that the fleet was caught above the rapids
near Alexandria, and it would in all probability have been a complete
loss had it not been for the timely application of engineering skill
by Lieut. Col. Joseph Bailey, a civil engineer from Wisconsin, who
built a temporary dam across the river below the rapids and floated
out the entire fleet. This dam was over 750 feet long and in
connection with some auxiliary dams raised the water level some 6½
feet. It was built under many difficulties, but by the skill and
ability of the engineer and the co-operation of the troops it was
completed in ten days. Another case was at the siege of Petersburg,
Va., where Lieut. Col. Pleasants, a Pennsylvania coal miner, ran a
gallery from our lines, under the rebel battery, some 500 feet
distant, and blew it entirely out of existence. The mine contained
four tons of powder and produced a crater 200 feet by 50 feet and 25
feet deep, and was completed in one month. The sequel to this was to
be an attack on the enemy's line through the gap made by the
explosion, and such an attack properly followed up would doubtless
have had a marked effect in shortening the duration of the war, but
this attack was so badly managed that it utterly failed and caused a
severe loss to our own army. The mine itself, however, was a great
success and produced a decided moral effect on both sides which lasted
until the end of the war.

It may be out of place to digress a moment to illustrate the moral
effect of such a convulsion. Several weeks after this great mine
explosion, the 18th Army Corps, to which I then belonged, was holding
a line of works recently captured from the rebels, about six miles
from Richmond, when one night the colonel commanding Fort Harrison, a
large field work forming a part of this line, came down to
headquarters and reported that some old Pennsylvania coal miners in
his command had heard mining going on under the fort. As the nearest
part of the enemy's line was some 400 yards from the fort, I was quite
certain that they could not have run a gallery that distance in the
time that had elapsed since we occupied the work, but there was of
course the possibility that the mine had been partly built beforehand
so as to be ready in just such a case as had arisen, viz., the capture
of the fort by our troops. I therefore went with the colonel up to the
fort to listen for the mining operations, and got the men who claimed
to have heard the subterranean noises, down in the bottom of the ditch
of the fort, which was ten feet deep, and at the angles formed a
fairly good listening gallery, but nothing unusual could be heard. I
therefore made arrangements to sink a line of pits in the bottom of
the ditch, something like ordinary wells; the bottoms of these pits to
be finally connected by a horizontal gallery which would envelop the
fort and enable us to hear the enemy and blow him up, before he could
get under the fort. Although the commanding officer of that fort was
as brave an officer as the war developed, he would not keep his men in
the fort after dark, but withdrew them quietly to the flanks of the
work, where they not only would be safe from an explosion, but would
be ready to fall upon the enemy in case he should blow up the fort and
rush in to capture the line, as our troops had attempted to do at
Petersburg. No explosion took place, however, and after our
countermining work was completed, the garrison became reassured and
remained in the fort at night as well as in day time. A few months
later, when the enemy was driven from his lines, I went through his
works to see whether any mining had been attempted, and found that a
gallery leading toward Fort Harrison had been carried quite a
distance, but was still incomplete, and it is barely possible that the
old miners were right, after all, in thinking that they could hear the
sound of the pick, although the distance was almost too great to make
this theory very probable.

Still another illustration of the way in which civil engineers can
make themselves extremely useful in military operations was the
wonderful system of military railways, or railways operated for
military purposes, that formed complete lines of transportation for
the armies and their enormous quantities of supplies and munitions,
more especially those in the West and Southwest. Construction trains
were organized in the most complete style, and when a piece of track
or a number of bridges were destroyed by the enemy, they would be
rebuilt so rapidly that our trains would hardly seem to be delayed by
it. The trains carried spare rails, ties, and bridges of various
lengths ready to put up, and they also carried the necessary rolling
stock and tools for destroying the roads and bridges of the enemy. So
expert had this construction corps become that the enemy was ready to
believe almost any statement in regard to it. General Sherman tells of
an instance where it was proposed to blow up a tunnel, to check his
"March to the Sea," when one of the men objected, saying it was of no
use, for Sherman had a duplicate tunnel in his train.

Although this is not a sermon, it may not be out of place to point out
a few qualifications common to all engineers, for they all deal more
or less with the same materials and forces and employ similar methods
of investigation and construction. Wood, iron, steel, copper and stone
and their compounds are the materials of the civil, mining, mechanical
and electrical, as well as of the military engineers. They all deal
with the forces of gravitation, cohesion, inertia and chemical
affinity. They all require skill, intelligence, industry, confidence,
accuracy, thoroughness, ingenuity and, beyond all, sound judgment.
Wanting in any one of these qualifications, an engineer is more or
less disqualified for important work. It is said that a distinguished
engineer was always afraid to cross his own bridges, although built in
the most thorough and approved manner. He was deficient in confidence.
Another engineer distinguished for his mathematical attainments built
a bridge which promptly collapsed at the first opportunity. On
overhauling his computations he ejaculated somewhat forcibly, "That
confounded minus sign! It should have been plus." He was deficient in
sound judgment, or what is sometimes called "horse sense."

Another and more common defect in young engineers is a want of
thoroughness. It is generally best to go to the bottom of a question
at first and keep at it until it is thoroughly and fully completed.
Confucius says, "If thou hast aught to do, first consider, second act,
third let the soul resume her tranquillity." Those who begin a great
many things and never fully complete them lose a great deal of
valuable time, but do very little valuable work. The way to avoid this
difficulty is to be cautious about beginning things, but when once
started don't leave it until you are satisfied to leave it for good.
There is an Arabian saying, "Never undertake _all_ you can do, for he
who undertakes _all_ he can do will frequently undertake _more_ than
he can do."

Another common error is extravagance. On the plea that "the best is
always the cheapest," and to be sure of a large factor of safety, or
as the late Mr. Holley called it a "factor of ignorance," without much
trouble to themselves, some engineers use more or better materials
than the work requires, and thus greatly increase the cost without any
corresponding advantage. Almost any engineer can do almost anything in
the way of engineering if not limited by the cost, but the man who
knows just what materials to use and how to use them so that they will
answer the purpose as to strength and durability can save his own
salary to his employer many times over by simply omitting unnecessary
expense.

* * * * *




HOW MECHANICAL RUBBER GOODS ARE MADE.


While the manufacture of rubber goods is in no sense a secret
industry, the majority of buyers and users of such goods have never
stepped inside of a rubber mill, and many have very crude ideas as to
how the goods are made up. In ordinary garden hose, for instance, the
process is as follows: The inner tubing is made of a strip of rubber
fifty feet in length, which is laid on a long zinc-covered table and
its edges drawn together over a hose pole. The cover, which is of what
is called "friction," that is cloth with rubber forced through its
meshes, comes to the hose maker in strips, cut on the bias, which are
wound around the outside of the tube and adhere tightly to it. The
hose pole is then put in something like a fifty foot lathe, and while
the pole revolves slowly, it is tightly wrapped with strips of cloth,
in order that it may not get out of shape while undergoing the process
of vulcanizing. When a number of these hose poles have been covered in
this way they are laid in a pan set on trucks and are then run into a
long boiler, shut in, and live steam is turned on. When the goods are
cured steam is blown off, the vulcanizer opened and the cloths are
removed. The hose is then slipped off the pole by forcing air from a
compressor between the rubber and the hose pole. This, of course, is
what is known as hose that has a seam in it.

For seamless hose the tube is made in a tubing machine and slipped
upon the hose pole by reversing the process that is used in removing
hose by air compression. In other words, a knot is tied in one end of
the fifty foot tube and the other end is placed against the hose pole
and being carefully inflated with air it is slipped on without the
least trouble. For various kinds of hose the processes vary, and there
are machines for winding with wire and intricate processes for the
heavy grades of suction hose, etc. For steam hose, brewers', and acid
hose, special resisting compounds are used, that as a rule are the
secrets of the various manufacturers. Cotton hose is woven through
machines expressly designed for that purpose, and afterward has a
half-cured rubber tube drawn through it. One end is then securely
stopped up and the other end forced on a cone through which steam is
introduced to the inside of the hose, forcing the rubber against the
cotton cover, finishing the cure and fixing it firmly in its place.


CORRUGATED MATTING.

After the mixing of the compound and the calendering, that is the
spreading it in sheets, the great roll of rubber and cloth that is to
be made into corrugated matting is sent to the pressman. Here it is
hung in a rack and fifteen or twenty feet of it drawn between the
plates of the huge hydraulic steam press. The bottom plate of this
press is grooved its whole length, so that when the upper platen is
let down the plain sheet of rubber is forced into the grooves and the
corrugations are formed. While in that position steam is let into the
upper and lower platens and the matting is cured. After it has been in
there the proper time, cold water is let into the press, it is cooled
off, and the upper platen being raised, it is ready to come out. A
simple device for loosening the matting from the grooves into which it
has been forced is a long steel rod, with a handle on one hand like an
auger handle, which, being introduced under the edge and twisted,
allows the air to enter with it and releases it from the mould.


PACKING.

Sheet packing is often times made in a press, like corrugated matting.
The varieties, however, known as gum core have to go through a
different process. Usually a core is squirted through a tube machine
and the outside covering of jute or cotton, or whatever the fabric may
be, is put on by a braider or is wrapped about it somewhat after the
manner of the old fashioned cloth-wrapped tubing. The fabric is either
treated with some heat-resisting mixture or something that is a
lubricant, plumbago and oil being the compound. Other packings are
made from the ends of belts cut out in a circular form and treated
with a lubricant. There are scores of styles that make special claims
for excellences that are made in a variety of ways, but as a rule the
general system as outlined above is followed.


JAR RINGS.

The old fashioned way of making jar rings was first to take a large
mandrel and wrap it around with a sheet of compounded rubber until the
thickness of the ring was secured. It was then held in place by a
further wrapping of cloth, vulcanized, put in a lathe and cut up into
rings by hand. That manner of procedure, however, was too slow, and it
is to-day done almost wholly by machinery. For example, the rubber is
squirted out of a mammoth tubing machine in the shape of a huge tube,
then slipped on a mandrel and vulcanized. It is then put in an
automatic lathe and revolving swiftly is brought against a sharp
knife blade which cuts ring after ring until the whole is consumed,
without any handling or watching. - _India Rubber World_.

* * * * *




HOW ENAMELED LETTERS ARE MADE.


The following is a description of a brief visit by a representative of
the _Journal of Decorative Art_ to the new factory of the Patent
Letter and Enamel Company, Ltd., situate in the East End of London.

The company have recently secured a large freehold plot in the center
of the East End of London, and have built for themselves a most
commodious and spacious factory, some hundreds of feet in length, all
on one floor, and commanded from one end by the manager's office, from
whence can be seen at a glance the entire premises.

The works are divided into two large compartments, and are lighted
from the roof, ample provision being made for ventilation, and
attention being given to those sanitary conditions which are, or
should be, imperative on all well managed establishments.

We first explore the stockroom. Here are stored the numerous dies, of
all sizes and shapes, which the company possess, varying in size from
half an inch to twelve or sixteen inches. Here, too, is kept the large
store of thin sheet copper out of which the letters are stamped. Our
readers are familiar with the form or principle upon which these
letters are made. It is simply a convex surface, the reverse side
being concave, and being fixed on to the glass or other material with
a white lead preparation. When these letters were first made, the
practice was to cut or stamp them out in flat copper, and then to
round or mould them by a second operation. Recent improvements in the
machinery, however, have dispensed with this dual process, and the
stamping and moulding is done in the one swift, sharp operation.

The process of making an enameled letter has four stages - stamping,
enameling, firing, and filing. There are other and subsequent
processes for elaborating, but those named are of the essence of the
transaction.


STAMPING.

The stamping is done by means of presses, and is a very rapid and
complete operation.

The operator takes a piece of the sheet copper, places it on the
press, the lever descends, there is a sharp crunching, bursting sound,
and in a time shorter than it has taken to describe, the letter is
made, sharp and perfect in every way.


ENAMELING.

The letters are now taken charge of by a girl, who lays them out on a
wire tray, the hollow side up, and paints them over with a thin
mordant. While they are in this position, and before the mordant
dries, they are taken on the gridiron-like tray to a kind of large
box, which is full of the powdered enamel, and, holding the tray in
her left hand, the girl takes a fine sieve full of the powder and
dusts it over the letter, all superfluous powder falling through the
open wirework and into the bin again, so that there is absolutely no
waste.

[Illustration: DUSTING THE LETTERS BEFORE FIRING.]


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Online LibraryVariousScientific American Supplement, No. 841, February 13, 1892 → online text (page 8 of 11)