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Scientific American Supplement, No. 520, December 19, 1885 online

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consisted of concrete, formed with Roman cement so hard that it turns the
points of pickaxes when employed against it, with layers of tiles at
regular intervals. The surface of the concrete is covered with small
cubical blocks of stone placed so that their diagonals are horizontal and
vertical, and forming what is known as _opus reticulatum_. After crossing
the bridge the pipes were carried up the other side of the valley into a
reservoir, of which little remains, and then the aqueduct was continued
to the next valley, passing over three bridges in its course. This
valley, that of St. Irenée, is much smaller than either of the others,
but nevertheless it was deep enough to necessitate the construction of
inverted siphons, of which there were eight. Leaving the reservoir on the
other side of this valley, the aqueduct was carried on a long bridge (the
twentieth on its course) which crossed the plateau on the top of
Fourvieres and opened into a large reservoir, the remains of which are
still to be seen on the top of that hill.

From this reservoir, which was 77 ft. long and 51 ft. wide, pipes of lead
conveyed the water to the imperial palace and to the other buildings near
the top of the hill. Some of these lead pipes were found in a vineyard
near the top of Fourvieres at the beginning of the eighteenth century,
and were described by Colonia in his history of Lyons. They are made of
thick sheet lead rolled round so as to form a tube, with the edges of the
sheet turned upward, and applied to one another in such a way as to leave
a small space, which was probably filled with some kind of cement. These
pipes, of which it is said that twenty or thirty, each from 15 ft. to 20
ft. long, were found, were marked with the initial letters TI. CL. CAES.
(Tiberius Claudius Cæsar), and afford positive evidence that the work was
carried out under the emperor Claudius. Lead pipes, constructed in a
similar manner, have also been found at Bath, in this country, in
connection with the Roman baths. The great difference between this
aqueduct and those near Rome arises from the fact that, instead of being
carried across a nearly flat country, it was carried across one
intersected with deep ravines, and that it was therefore necessary to
have recourse to the system of inverted siphons. There can be no doubt
that the inverted siphons were made of lead, although no remains of them
have been found; for we know that the Romans used lead largely, and, as
we have seen, pieces of the lead distribution pipes have been found. It
is possible, and even likely, that strong cords of hemp were wound round
the pipes forming the siphons, as is related by Delorme in describing a
similar Roman aqueduct siphon near Constantinople; Delorme also
describes, in the aqueduct last mentioned, a pipe for the escape of air
from the lowest part of the siphon carried up against a tower, which was
higher than the aqueduct, and it is certain that there must have been
some such contrivance on the siphons of the aqueduct constructed at
Lyons.

Flacheron supposes that they consisted of small pipes carried from the
lowest part of the siphons up along the side of the valley and above the
reservoirs, or, in some instances, of taps fixed at the lowest part of
the siphons. The Romans have been blamed for not using inverted siphons
in the aqueducts at Rome, and it has been said that this is a sufficient
proof that they did not understand the simplest principles of hydraulics,
but the remains of the aqueducts at Lyons negative this assumption
altogether. The Romans were not so foolish as to construct underground
siphons, many miles long, for the supply of Rome; but where it was
necessary to construct them for the purpose of crossing deep valleys,
they did so. The same emperor Claudius who built the aqueduct at Rome
known by his name built the aqueduct of Mont Pila, at Lyons, and it is
quite clear, therefore, that his engineers were practically well
acquainted with the principles of hydraulics. It is thus seen that the
ancient Romans spared no pains to obtain a supply of pure water for their
cities, and I think it is high time that we followed their example, and
went to the trouble and expense of obtaining drinking water from
unimpeachable sources, instead of, as is too often the case, taking
water which we know perfectly well has been polluted, and then attempting
to purify it for domestic purposes.

* * * * *




STEAM ENGINE ECONOMY.

By Chief Engineer JOHN LOWE, U.S. Navy.


The purpose of this article is to point out an easy method whereby any
intelligent engineer can determine the point at which it is most
economical to cut off the admission of steam into his cylinder.

In the attack upon such a problem, it is useful to employ all the senses
which can be brought to bear upon it; for this purpose, diagrams will be
used, in order that the sense of sight may assist the brain in forming
its conclusions.

[Illustration: STEAM ENGINE ECONOMY. - BY JOHN LOWE, CHIEF ENGINEER
U.S.N.]

Fig. XABCX is an ideal indicator card, taken from a cylinder, imagined to
be 600 feet long, in which the piston, making one stroke per minute, has
therefore a piston speed of 600 feet per minute. Divide this card into
any convenient number of ordinates, distant _dx_ feet from each other,
writing upon each the absolute pressure measured upon it from the zero
line XX.

By way of example, let the diameter of the cylinder be 29.59 inches, and
let the back pressure from all causes be 7 pounds uniformly throughout.
It will be represented by the line b_{1}, b_{2}, etc. This quantity
subtracted from the pressures p_{1}, p_{2}, etc., leaves the remainder
(p-b) upon each ordinate, which remainder represents the net pressures
which at that point may be applied to produce external power.

If, now, A is the area of the piston, then the external power (d W)
produced between each ordinate is:

To any convenient scale, upon each ordinate, set off the appropriate
power as calculated by this equation (1).

A(p-b)dx
dW = - - - - - - - . (1.)
33,000

There will result the curve _w, w, w_, determining the power which at any
point in the diagram is to be regarded as a gain, to be carried to the
credit side of the account.

It is evident that, so long as the gains from expansion exceed the losses
from expansion, it is profitable to proceed with expansion, but that
expansion should cease at that point at which gains and losses just
balance each other.


TO CALCULATE THE LOSSES.

The requisite data are furnished by the experiments conducted some years
since by President D.M. Greene, of Troy College, for the Bureau of Steam
Engineering, U.S. Navy.

According to these experiments, the heat which is lost per hour by
radiation through a metallic plate of ordinary thickness, exposed to dry
air upon one side and to the source of heat upon the other, for one
degree difference in temperature, is as follows:

Condition. Heat units.

Naked...................................... 2.9330672
Covered with hair felt, 0.25 inch thick.... 1.0540710
" " 0.50 " .... 0.5728647
" " 0.75 " .... 0.4124625
" " 1.00 " .... 0.3070554
" " 1.25 " .... 0.2746387
" " 1.50 " .... 0.2507097

If now t' = temperature of steam at the ordinate,
t = temperature of the surrounding atmosphere,
dS = surface of the cylinder included between each ordinate,
k = that figure from the table satisfying the conditions,
then the power loss (dR) per minute will be:

k (t'-t)dS
dR = ( - ) - - - - - . (2)
60 33,000


To the same scale as the power gains, upon each ordinate, set off the
appropriate power loss, as calculated by this equation (2).

There will result the curve r, r, r, which determines the power which at
any point in the diagram is to be regarded as a loss, to be carried to
the debit side of the account. This curve of losses intersects the curve
of gains at a point (it is evident) where each equals the other.

Therefore this is the point at which expansion should cease, and this
absolute pressure is the economic terminal pressure, which determines the
number of expansions profitable under the given conditions.

In the foregoing example are taken k = 0.3070554, t' = 331.169, t = 60,
while the back pressure was taken at 7 pounds.

By way of further illustration, first let the back pressure be changed
from 7 to 5.

By equation 1 there will result a new curve of gains, W, W, W, a portion
only being plotted.

Second, let t' = 331.169 as before.
t = 150 instead of 60.
k = 0.2507097 instead of 0.3070554.

There will result the second curve of losses, R, R, R, intersecting the
second curve of gains at the point F, the new economic point for our new
conditions.

These two examples fully illustrate the whole subject, furnishing an easy
and, when carefully made, a very exact calculation and result.

The following are a few of the general conclusions to be drawn:

1. That radiation is a tangible and measurable cause, sufficient to
account for all losses heretofore ascribed to an intangible,
immeasurable, and wholly imaginary cause, viz., "internal evaporation and
re-evaporation."

2. In order to prevent the high initial temperatures now used becoming a
source of loss, it is necessary to prevent the quantity dS (t'-t)
becoming great, by making dS as small as possible. In other words, we
must compound our engines. Thus for the first time is pointed out the
true reason why compound engines are economical heat engines.

3. The foregoing reasoning being correct, it follows that steam jackets
are a delusion.

4. In order to attain economy, we must have high initial temperatures,
small high pressure cylinders, low back pressures from whatsoever cause,
high piston speeds, short rather than long strokes, to avoid the cooling
effects of a long piston rod; but especially must we have scrupulous and
perfect protection from radiation, especially about the cylinder heads,
now oftentimes left bare.

* * * * *




ELECTRICITY IN WARFARE.

[Footnote: From a recent lecture before the Franklin Institute,
Philadelphia.]

By Lieut. B.A. FISKE, U.S.N.


Lieutenant Fiske began by paying a tribute to the remarkable pioneer
efforts of Colonel Samuel Colt, who more than forty years ago blew up
several old vessels, including the gunboat Boxer and the Volta, by the
use of electricity. Congress voted Colt $17,000 for continuing his
experiments, which at that day seemed almost magical; and he then blew up
a vessel in motion at a distance of five miles. Lieut. Fiske next
referred briefly to the electrical torpedoes employed in the Crimean war
and our civil war.

At the present day, an electrical torpedo may be described as consisting
of a strong, water-tight vessel of iron or steel, which contains a large
amount of some explosive, usually gun-cotton, and a device for detonating
this explosive by electricity. The old mechanical mine used in our civil
war did not know a friendly ship from a hostile one, and would sink
either with absolute impartiality. But the electrical submarine mine,
being exploded only when a current of electricity is sent through it from
ship or shore, makes no such mistake, and becomes harmless when detached
from the battery. The condition of the mine at any time can also be told
by sending a very minute current through it, though miles away and buried
deep beneath the sea.

When a current of electricity goes through a wire, it heats it; and if
the current be made strong enough, and a white hot wire thus comes in
contact with powder or fulminate of mercury in a torpedo, an explosion
will result. But it is important to know exactly when to explode the
torpedo, especially during the night or in a fog; and hence torpedoes are
often made automatic by what is called a circuit closer. This is a device
which automatically bridges over the distance between two points which
were separated, thus allowing the current to pass between them. In
submarine torpedoes it is usual to employ a small weight, which, when the
torpedo is struck, is thrown by the force of the blow across two contact
points, one of which points is in connection with the fuse and the other
in connection with the battery, so that the current immediately runs over
the bridge thus offered, and through the fuse. In practice, these two
contact points are connected by a wire, even when the torpedo is not in
the state of being struck; but the wire is of such great resistance that
the current is too weak to heat the wire in the fuse. Yet when the weight
above mentioned is thrown across the two contact points, the current runs
across the bridge, instead of through the resistance wire, and is then
strong enough to heat the wire in the fuse and explode the torpedo. The
advantage of having a wire of high resistance between the contact points,
instead of having no wire between them, is that the current which then
passes through the fuse, though too weak to fire it, shows by its very
existence to the men on shore that the circuit through the torpedo is all
right.

But instead of having the increased current caused by striking the
torpedo to fire the torpedo directly, a better way is to have it simply
make a signal on shore. Then, when friendly vessels are to pass, the
firing battery can be disconnected; and when the friendly ship bumps the
torpedo, the working of the signal shows not only that the circuit
through the fuse is all right, but also that the circuit closer is all
right, so that, had the friendly ship been a hostile ship, she would
certainly have been destroyed.

While the management of the torpedo is thus simple, the defense of a
harbor becomes a complex problem, on account of the time and expense
required to perfect it, and the training of a corps of men to operate the
torpedoes.

In order to detect the presence of torpedoes in an enemy's harbor, an
instrument has been invented by Capt. McEvoy, called the "torpedo
detecter," in which the action is somewhat similar to that of the
induction balance, the iron of a torpedo case having the effect of
increasing the number of lines of force embraced by one of two opposing
coils, so that the current induced in it overpowers that induced in the
other, and a distinct sound is heard in a telephone receiver in circuit
with them. As yet, this instrument has met with little practical success,
but, its principle being correct, we can say with considerable confidence
that the reason of its non-success probably is that the coils and current
used are both too small.

Lieut. Fiske described the spar torpedo and the various classes of
movable torpedoes, including the Lay. His conclusion is that the most
successful of the movable torpedoes is the Simms, with which very
promising experiments have been conducted under the superintendence of
Gen. Abbot.

Recent experiments in England have shown that the Whitehead torpedo, over
which control ceases after it is fired, is not so formidable a weapon
when fired at a ship _under way_ as many supposed, for the simple reason
that it can be dodged. But an electrical torpedo, over which control is
exercised while it is in motion through the water, cannot be dodged,
provided it receives sufficient speed. For effective work against ships
capable of steaming fifteen knots per hour, the torpedo should have a
speed of twenty knots. There is no theoretical difficulty in the way of
producing this, for a speed of eleven knots has already been recorded,
though an electric torpedo, to get this speed, would have to be larger
than a Whitehead having the same speed. It may be conceived that a
torpedo carrying 50 lb. of gun-cotton, capable of going 20 knots per
hour, so that it would pass over a distance of 500 yards in about 45
sec., and yet be absolutely under control all the time, so that it can be
constantly kept pointed at its target, would be a very unpleasant thing
for an enemy to meet.

Military telegraphy is a second use of electricity in warfare. Lieut.
Fiske traces its origin to our own civil war. Foreign nations took the
hint from us, and during the invasion of France the telegraph played a
most important part. In military telegraph trains, miles of wire are
carried on reels in specially constructed wagons, which hold also
batteries and instruments. Some of the wire is insulated, so that it can
rest on the ground, and thus be laid out with great speed, while other
wire is bare, and is intended to be put on poles, trees, etc. For
mountain service the wires and implements are carried by pack animals.
Regularly trained men are employed, and are drilled in quickly running
lines, setting up temporary stations, etc. In the recent English
operations in Egypt, the advance guard always kept in telegraphic
communication with headquarters and with England, and after the battle of
Tel-el-Kebir news of the victory was telegraphed to the Queen and her
answer received in forty-five minutes.

The telephone is also used with success in warfare, and in fact sometimes
assists the telegraph in cases where, by reason of the haste with which a
line has been run, the current leaks off. A telephone may then be used to
receive the message - and for a transmitter a simple buzzer or automatic
circuit breaker, controlled by an ordinary key. In the case of vessels
there is much difficulty in using the telegraph and the telephone, as the
wire may be fouled and broken when the ship swings by a long chain. In
England in the case of a lightship this difficulty has been surmounted,
or rather avoided, by making hollow the cable by which the ship rides,
and running an insulated wire along the long tube thus formed inside. But
the problem is much simplified when temporary communication only is
desired between ships at anchor, between a ship and the shore, or even
between a ship and a boat which has been sent off on some special
service, such as reconnoitering, sounding, etc. In this case portable
telephones are used, in which the wire is so placed on a reel in circuit
with the telephone that communication is preserved, even while the wire
is running off the reel.

The telegraph and telephone are both coming largely into use in artillery
experiments, for example, in tracking a vessel as she comes up a channel
so that her exact position at each instant may be known, and in
determining the spot of fall of a projectile. In getting the time of
flight of projectiles electricity is of value; by breaking a wire in
circuit with a chronograph, the precise instant of start to within a
thousandth of a second being automatically registered. Velocimeters are a
familiar application of electricity somewhat analogous. In these, wires
are cut by the projectile at different points in its flight, and the
breaking of the electric current causes the appearance of marks on a
surface moving along at a known speed. The velocity of the projectile in
going from one wire to another can then be found.

Electricity is also used for firing great guns, both in ships and forts.
In the former, it eliminates the factor of change produced by the rolling
of the ship during the movement of the arm to fire the gun. The touch of
a button accomplishes the same thing almost instantaneously. Moreover, an
absolutely simultaneous broadside can be delivered by electricity. The
officer discharges the guns from a fighting tower, whither the wires
lead, and the men can at once lie down out of the enemy's machine guns,
as soon as their own guns are ready for discharge. The electric motor
will certainly be used very generally for handling ordnance on board
ships not very heavily plated with armor, since a small wire is a much
more convenient mode of conveying energy to a motor of any kind, and is
much less liable to injury, than a comparatively large pipe for conveying
steam, compressed air, or water under pressure. Besides, the electric
motor is the ideal engine for work on shipboard, by reason of its smooth
and silent motion, its freedom from dirt and grease, the readiness with
which it can be started, stopped, and reversed, and its high efficiency.
Indeed, in future we may look to a protected apparatus for all such uses
in every fort and every powerful ship.

In photographing the bores of great guns, electric lights are used, and
they make known if the gun is accurately rifled and how it is standing
the erosion of the powder gases.

In the case of a fort, electricity can be employed in connection with the
instruments used for determining at each instant the position of an
approaching vessel or army. Whitehead torpedoes are now so arranged that
they can be ejected by pressing an electric button.

Electric lights for vessels are now of recognized importance. At first
they were objected to on the ground that if the wire carrying the current
should be shot away in action, the whole ship would be plunged in
darkness; and so it would be in an accident befalling the dynamo that
generates the current. The criticism is sensible, but the answer is that
different circuits must be arranged for different parts of the ship, and
the wires carrying the current must be arranged in duplicate. It is also
easy to repair a break in a copper wire if shot away. As to the dynamo
and engines, they must be placed below the water line, under a protective
deck, and this should be provided for in building the vessel. There
should be several dynamos and engines. All the dynamos should, of course,
be of the same electromotive force, and feed into the same mains, from
which all lamps draw their supply, and which are fed by feeders from the
dynamo at different points, so that accident to the mains in one part of
the ship will affect that part only. But it is the arc light, used as
what is called a search light, that is most valuable in warfare. Lieut.
Fiske thinks its first use was by the French in the siege of Paris, to
discover the operations of the besiegers. It can be carried by an army in
the field, and used for examining unknown ground at night, searching for
wounded on the battle field, and so on. On fighting vessels the search
light is useful in disclosing the attack of torpedo boats or of hostile
ships, in bringing out clearly the target for guns, and in puzzling an
enemy by involving him successively in dazzling light and total darkness.
Lieut. Fiske suggests that this use would be equally effective in
embarrassing troops groping to the attack of a fort at night by sudden
alternations of blinding light and paralyzing darkness. There should be
four search lights on each side of a ship.

As to the power and beauty of the search light, Lieut. Fiske refers to
the magnificent one with which he lighted up Philadelphia last autumn,
during the electric exhibition in that city. One night he went to the
tower of the Pennsylvania railroad station and watched the light
stationed at the Exhibition building on 32d street. The ray of light when
turned at right angles to his direction looked like a silver arrow going
through the sky; and when turned on him, he could read the fine print of
a railroad time table at arm's length. Flashes from his search light were
seen at a distance of thirty miles.

In using incandescent lamps for night signaling, the simplest way is to
arrange a keyboard with keys marked with certain numbers, indicating the
number of lamps arranged in a prominent position, which will burn while
that key is being pressed. For example, suppose the number 5348 means
"Prepare to receive a torpedo attack." Press keys 5, 3, 4, 8, and the
lights of lamps 5, 3, 4, 8, successively blaze out.

Electrical launches have been used to some extent, their storage
batteries being first charged ashore or on board the ship to which the
launch belongs. They have carried hundreds of people, and have made eight
knots an hour. The improvement of storage batteries, steadily going on,
will eventually cause the electrical launch to replace the steam launch.
One of its advantages is in having no noise from an exhaust and no flame
flaring above a smoke pipe to betray its presence. In warfare two sets of
storage batteries should be provided for launches, one being recharged
while the other is in use.

Mr. Gastine Trouse has recently invented "an electric sight," a filament
of fine wire in a glass tube covered with metal on all sides save at the


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Online LibraryVariousScientific American Supplement, No. 520, December 19, 1885 → online text (page 5 of 9)