Scientific American Supplement, No. 385, May 19, 1883

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Small pieces of combustible material were piled up beforehand on the two
altars, the bodies of which were of metal, and in the interior of which
were hidden small lamps that were separated from the combustible by a
metal plate which was drawn aside at the proper moment by a small
chain. The flame, on traversing the orifice, thus communicated with the
combustible.

The milk and wine which flowed out at two different times through the
thyrsus and cup of Bacchus came from a double reservoir hidden under the
roof of the temple, over the orifices. The latter communicated, each of
them, with one of the halves of the reservoir through two tubes inserted
in the columns of the small edifice. These tubes were prolonged under
the floor of the stage, and extended upward to the hands of Bacchus. A
key, maneuvered by cords, alternately opened and closed the orifices
which gave passage to the two liquids.

As for the noise of the drums and cymbals, that resulted from the
falling of granules of lead, contained in an invisible box provided with
an automatic sliding-valve, upon an inclined tambourine, whence they
rebounded against little cymbals in the interior of the base of the car.

[Illustration: FIG. 2.--MARVELOUS ALTAR (According to Heron).]

Finally, the crowns and garlands that suddenly made their appearance on
the four faces of the base of the stage were hidden there in advance
between the two walls surrounding the base. The space thus made for the
crowns was closed beneath, along each face, by a horizontal trap moving
on hinges that connected it with the inner wall of the base, but which
was held temporarily stationary by means of a catch. The crowns were
attached to the top of their compartment by cords that would have
allowed them to fall to the level of the pedestal, had they not been
supported by the traps.

At the desired moment, the catch, which was controlled by a special
cord, ceased to hold the trap, and the latter, falling vertically, gave
passage to the festoons and crowns that small leaden weights then drew
along with all the quickness necessary.

Two points here are specially worthy of attracting our attention, and
these are the flow of wine or milk from the statue of Bacchus, and
the spontaneous lighting of the altar. These, in fact, were the two
illusions that were most admired in ancient times, and there were
several processes of performing them. Father Kircher possessed in his
museum an apparatus which he describes in _Oedipus Egyptiacus_ (t. ii.,
p. 333), and which probably came from some ancient Egyptian temple.
(Fig. 1.)

It consisted of a hollow hemispherical dome, supported by four columns,
and placed over the statue of the goddess of many breasts. To two of
these columns were adapted movable brackets, at whose extremities there
were fixed lamps. The hemisphere was hermetically closed underneath by a
metal plate. The small altar which supported the statue, and which was
filled with milk, communicated with the interior of the statue by a tube
reaching nearly to the bottom. The altar likewise communicated with
the hollow dome by a tube having a double bend. At the moment of the
sacrifice the two lamps were lighted and the brackets turned so that the
flames should come in contact with and heat the bottom of the dome. The
air contained in the latter, being dilated, issued through the tube, X
M, pressed on the milk contained in the altar, and caused it to rise
through the straight tube into the interior of the statue as high as
the breasts. A series of small conduits, into which the principal tube
divided, carried the liquid to the breasts, whence it spurted out, to
the great admiration of the spectators, who cried out at the miracle.
The sacrifice being ended, the lamps were put out, and the milk ceased
to flow.

Heron, of Alexandria, describes in his _Pneumatics_ several analogous
apparatus. Here is one of them. (We translate the Greek text literally.)

[Illustration: Fig. 3.--MARVELOUS ALTAR (According to Heron).]

"To construct an altar in such a way that, when a fire is lighted
thereon, the statues at the side of it shall make libations. (Fig. 2.)

"Let there be a pedestal. A B [Gamma] [Delta], on which are placed
statues, and an altar, E Z H, closed on every side. The pedestal should
also be hermetically closed, but is communicated with the altar through
a central tube. It is traversed likewise by the tube, e [Lambda] (in
the interior of the statue to the right), not far from the bottom which
terminates in a cup held by the statue, e. Water is poured into the
pedestal through a hole, M, which is afterward corked up.

"If, then, a fire be lighted on the altar, the internal air will be
dilated and will enter the pedestal and drive out the water contained in
it. But the latter, having no other exit than the tube, e [Lambda], will
rise into the cup, and so the statue will make a libation. This will
last as long as the fire does. On extinguishing the fire the libation
ceases, and occurs anew as often as the fire is relighted.

"It is necessary that the tube through which the heat is to introduce
itself shall be wider in the middle; and it is necessary, in fact, that
the heat, or rather that the draught that it produces, shall accumulate
in an inflation in order to have more effect."

According to Father Kircher (_l. c._), an author whom he calls Bitho
reports that there was at Sais a temple of Minerva in which there was an
altar on which, when a fire was lighted, Dyonysos and Artemis (Bacchus
and Diana) poured milk and wine, while a dragon hissed.

It is easy to conceive of the modification to be introduced into the
apparatus above described by Heron, in order to cause the outflow of
milk from one side and of wine from the other.

After having indicated it, Father Kircher adds: "It is thus that Bacchus
and Diana appeared to pour, one of them wine, and the other milk, and
that the dragon seemed to applaud their action by hisses. As the people
who were present at the spectacle did not see what was going on within,
it is not astonishing that they believed it due to divine intervention.
We know, in fact, that Osiris or Bacchus was considered as the
discoverer of the vine and of milk; that Iris was the genius of the
waters of the Nile; and that the Serpent, or good genius, was the first
cause of all these things. Since, moreover, sacrifices had to be made to
the gods in order to obtain benefits, the flow of milk, wine, or water,
as well as the hissing of the serpent, when the sacrificial flame was
lighted, appeared to demonstrate clearly the existence of the gods."

In another analogous apparatus of Heron's, it is steam that performs the
role that we have just seen played by dilated air. But the ancients do
not appear to have perceived the essential difference, as regards motive
power, that exists between these two agents; indeed, their preferences
were wholly for air, although the effects produced were not very great.
We might cite several small machines of this sort, but we shall confine
ourselves to one example that has some relation to our subject. This
also is borrowed from Heron's _Pneumatics_. (Fig. 3.)

"Fire being lighted on an altar, figures will appear to execute a round
dance. The altars should be transparent, and of glass or horn. From the
fire-place there starts a tube which runs to the base of the altar,
where it revolves on a pivot, while its upper part revolves in a tube
fixed to the fire-place. To the tube there should be adjusted other
tubes (horizontal) in communication with it, which cross each other
at right angles, and which are bent in opposite directions at their
extremities. There is likewise fixed to it a disk upon which are
attached figures which form a round. When the fire of the altar is
lighted, the air, becoming heated, will pass into the tube; but being
driven from the latter, it will pass through the small bent tubes and
... cause the tube as well as the figures to revolve."

Father Kircher, who had at his disposal either many documents that we
are not acquainted with, or else a very lively imagination, alleges
(_Oedip. AEg._, t. ii., p. 338) that King Menes took much delight in
seeing such figures revolve.

Nor are the examples of holy fire-places that kindled spontaneously
wanting in antiquity.

Pliny (_Hist. Nat_., ii., 7) and Horace (_Serm., Sat. v._) tell us that
this phenomenon occurred in the temple of Gnatia, and Solin (Ch. V.)
says that it was observed likewise on an altar near Agrigentum.
Athenaeus (_Deipn_. i., 15) says that the celebrated prestidigitator,
Cratisthenes, of Phlius, pupil of another celebrated prestidigitator
named Xenophon, knew the art of preparing a fire which lighted
spontaneously.

Pausanias tells us that in a city of Lydia, whose inhabitants, having
fallen under the yoke of the Persians, had embraced the religion of the
Magi, "there exists an altar upon which there are ashes which, in color,
resemble no other. The priest puts wood on the altar, and invokes I
know not what god by harangues taken from a book written in a barbarous
tongue unknown to the Greeks, when the wood soon lights of itself
without fire, and the flame from it is very clear."

The secret, or rather one of the secrets of the Magi, has been revealed
to us by one of the Fathers of the Church (Saint Hippolytus, it is
thought), who has left, in a work entitled _Philosophumena_, which
is designed to refute the doctrines of the pagans, a chapter on the
illusions of their priests. According to him, the altars on which this
miracle took place contained, instead of ashes, calcined lime and a
large quantity of incense reduced to powder; and this would explain the
unusual color of the ashes observed by Pausanias. The process, moreover,
is excellent; for it is only necessary to throw a little water on the
lime, with certain precautions, to develop a heat capable of setting on
fire incense or any other material that is more readily combustible,
such as sulphur and phosphorus. The same author points out still another
means, and this consists in hiding firebrands in small bells that were
afterward covered with shavings, the latter having previously been
covered with a composition made of naphtha and bitumen (Greek fire).
As may be seen, a very small movement sufficed to bring about
combustion.--_A. De Rochas, in La Nature_.

* * * * *

TORPEDO BOATS.

There are several kinds of torpedoes. The one which is most used in the
French navy is called the "carried" torpedo (_torpille portee_), thus
named because the torpedo boat literally _carries_ it right under the
sides of the enemy's ship. It consists of a cartridge of about 20
kilogrammes of gun cotton, placed at the extremity of an iron rod, 12
meters in length, projecting in a downward direction from the fore part
of the boat. The charge is fired by an electric spark by means of an
apparatus placed in the lookout compartment. Our engraving represents an
attack on an ironclad by means of one of these torpedoes. Under cover of
darkness, the torpedo boat has been enabled to approach without being
disabled by the projectiles from the revolving guns of the man-of-war,
and has stopped suddenly and ignited the torpedo as soon as the latter
came in contact with the enemy's hull.

The water spout produced by the explosion sometimes completely covers
the torpedo boat, and the latter would be sunk by it were not
all apertures closed so as to make her a true buoy. What appears
extraordinary is that the explosion does not prove as dangerous to the
assailant as to the adversary. To understand this it must be remembered
that, although the material with which the cartridges are filled is of
an extreme _shattering_ nature, and makes a breach in the most resistant
armor plate, when in _contact_ with it, yet, at a distance of a few
meters, no other effect is felt from it than the disturbance caused by
the water. This is why a space of 12 meters, represented by the length
of the torpedo spar, is sufficient to protect the torpedo boat. The
attack of an ironclad, however, under the conditions that we have just
described, is, nevertheless, a perilous operation, and one that requires
men of coolness, courage, and great experience.

[Illustration: ATTACK BY A TORPEDO BOAT UPON AN IRON CLAD SHIP OF WAR.]

There is another system which is likewise in use in the French navy, and
that is the Whitehead torpedo. This consists of a metallic cylinder,
tapering at each end, and containing not only a charge of gun cotton,
but a compressed air engine which actuates two helices. It is, in fact,
a small submarine vessel, which moves of itself in the direction toward
which it has been launched, and at a depth that has been regulated
beforehand by a special apparatus which is a secret with the inventor.
The torpedo is placed in a tube situated in the fore part of the torpedo
boat, and whence it is driven out by means of compressed air. Once
fired, it makes its way under the surface to the spot where the shock of
its point is to bring about an explosion, and the torpedo boat is thus
enabled to operate at a distance and avoid the dangers of an immediate
contact with the enemy. Unfortunately this advantage is offset by grave
drawbacks; for, in the first place, each of the Whitehead torpedoes
costs about ten thousand francs, without counting the expense of
obtaining the right to use the patent, and, in the second place, its
action is very uncertain, since currents very readily change its
direction. However this may be, the inventor has realized a considerable
sum by the sale of his secret to the different maritime powers, most of
whom have adopted his system.

All our ports are provided with flotillas and torpedo boats, and with
schools in which the officers and men charged with this service are
trained by frequent exercises. It was near L'Orient, at Port Louis, that
we were permitted to be witnesses of these maneuvers, and where we saw
the torpedo boats that were lying in ambush behind Rohellan Isle glide
between the rocks, all of which appeared familiar to them, and start out
seaward at the first signal. It was here, too, that we were witnesses
of the sham attack against a pleasure yacht, shown in one of our
engravings. A torpedo boat, driven at full speed, stopped at one meter
from the said yacht with a precision that denoted an oft-repeated study.

[Illustration: MODE OF FIRING TORPEDOES.]

Before we close, we must mention some very recent experiments that have
been made with a torpedo analogous to Whitehead's, that is to say, one
that runs alone by means of helices actuated by compressed air, but
having the great advantage that it can be steered at a distance from the
very place whence it has been launched. This extraordinary result is
obtained by the use of a rudder actuated by an electric current which is
transmitted by a small metallic cable wound up in the interior of the
torpedo, and paying out behind as the torpedo moves forward on its
mission. The operator, stationed at the starting point, is obliged to
follow the torpedo's course with his eyes in order to direct it during
its submarine voyage. For this reason the torpedo carries a vertical
mast, that projects above the surface, and at the top of which is placed
a lantern, whose light is thrown astern but is invisible from the front,
that is, from the direction of the enemy. A trial of this ingenious
invention was made a few weeks ago on the Bosphorus, with complete
success, as it appears. From the shore where the torpedo was put into
the water, the weapon was steered with sufficient accuracy to cause it
to pass, at a distance of two kilometers, between two vessels placed in
observation at a distance apart of ten meters. After this, it was made
to turn about so as to come back to its starting point. What makes this
result the more remarkable is that the waters of the Bosphorus are
disturbed by powerful currents that run in different directions,
according to the place.--_L'Illustration_.

* * * * *

PICTET'S HIGH SPEED BOAT.

It is now nearly a year ago since we announced to our readers the
researches that had been undertaken by the learned physicist, Raoul
Pictet, in order to demonstrate theoretically and practically the forms
that are required for a fast-sailing vessel, and since we pointed out
how great an interest is connected with the question, while at the same
time promising to revert to the subject at some opportune moment. We
shall now keep our promise by making known a work that Mr. Pictet has
just published in the _Archives Physiques et Naturelles_, of Geneva,
in which he gives the first results of his labors, and which we shall
analyze rapidly, neglecting in doing so the somewhat dry mathematical
part of the article.

For a given tonnage and identical tractive stresses, the greater or less
sharpness of the fore and aft part of the keel allows boats to attain
different speeds, the sharper lines corresponding to the highest speeds,
but, in practice, considerably diminishing the weight of freight capable
of being carried by the boat.

[Illustration: FIG. 1. PICTET'S HIGH SPEED BOAT.

A. Lateral View. B. Plan. C. Section of the boiler room. D. Section of
the cabin.]

Mr. Pictet proposed the problem to himself in a different manner, and as
follows:

Determine by analysis, and verify experimentally, what form of keel will
allow of the quickest and most economical carriage of a given weight of
merchandise on water.

We know that for a given transverse or midship section, the tractive
stress necessary for the progression of the ship is proportional to the
_square_ of the velocity; and the motive power, as a consequence, to the
_cube_ of such velocity.

[Illustration: Fig. 2.--Diagram of tractive stresses at different
speeds.]

The _friction_ of water against the polished surfaces of the vessel's
sides has not as yet been directly measured, but some indirect
experiments permit us to consider the resistances due thereto as small.
The entire power expended for the progress of the vessel is, then,
utilized solely in displacing certain masses of water and in giving them
a certain amount of acceleration. The masses of water set in motion
depend upon the surface submerged, and their acceleration depends upon
the speed of the vessel. Mr. Pictet has studied a form of vessel in
which the greatest part possible of the masses of water set in motion
shall be given a vertical acceleration, and the smallest part possible
a horizontal one; and this is the reason why: All those masses of water
which shall receive a vertical acceleration from the keel will tend to
move downward and produce a vertical reaction in an upward direction
applied to the very surface that gives rise to the motion. Such reaction
will have the effect of changing the level of the floating body; of
lifting it while relieving it of a weight exactly equal to the value
of the vertical thrust; and of diminishing the midship section, and,
consequently, the motive power.

[Illustration: Fig. 3.--Diagram of variations in tractive stresses and
tonnage taken as a function of the speed.]

All those masses of water which receive a horizontal acceleration from
the keel run counter, on the contrary, to the propulsive stress, and it
becomes of interest, therefore, to bring them to a minimum. The vertical
stress is limited by the weight of the boat, and, theoretically, with an
infinite degree of speed, the boat would graze the water without being
able to enter it.

The annexed diagram (Fig. 1) shows the form that calculation has led Mr.
Pictet to. The sides of the boat are two planes parallel with its axis,
and perfectly vertical. The keel (properly so called) is formed by
the joining of the two vertical planes. The surface thus formed is a
parabola whose apex is in front, the maximum ordinate behind, and the
concavity directed toward the bottom of the water. The stern is a
vertical plane intersecting at right angles the two lateral faces and
the parabolic curve, which thus terminates in a sharp edge. The prow of
the boat is connected with the apex of the parabola by a curve whose
concavity is directed upward.

[Illustration: Fig. 4.--Diagram of the variations in the power as a
function of the speed.]

When we trace the curve of the tractive stresses in a boat thus
constructed, by putting the speeds in abscisses and the tractive
stresses in ordinates, we obtain a curve (Fig. 2) which shows that the
same tractive stress applied to a boat may give it three different
speeds, M, M', and M'', only two of which, M and M'', are stable.

Experimental verifications of this study have been partially realized
(thanks to the financial aid of a number of persons who are interested
in the question) through the construction of a boat (Fig. 1) by the
Geneva Society for the Construction of Physical Instruments. The vessel
is 20.25 m. in length at the water line, has an everywhere equal width
of 3.9 m., and a length of 16 m. from the stern to the apex of the
parabola of the keel. The bottom of the boat is nearly absolutely flat.
The keel, which is 30 centimeters in width, contains the shaft of the
screw. The boiler, which is designed for running at twelve atmospheres,
furnishes steam to a two cylinder engine, which may be run at will,
either the two cylinders separately, or as a _compound_ engine. The
bronze screw is 1.3 m. in diameter, and has a pitch of 2.5 m. The vessel
has two rudders, one in front for slight speeds, and the other at the
stern. At rest, the total displacement is 52,300 kilogrammes.
This weight far exceeds what was first expected, by reason of the
superthickness given the iron plates of the vertical sides, of the
supplementary cross bracing, and of the superposition of the netting
necessary to resist the flexion of the whole. On another hand,
the tractive stress of the screw, which should reach about 4,000
kilogrammes, has never been able to exceed 1,800, because of the
numerous imperfections in the engine. It became necessary, therefore,
to steady the vessel by having her towed by the _Winkelried_, which was
chartered for such a purpose, to the General Navigation Company. It
became possible to thus carry on observations on speeds up to 27
kilometers per hour.

Fig. 3 shows how the tractive stress varies with each speed in a
theoretic case (dotted curve) in which the stress is proportional to the
square of the speed, in Madame Rothschild's boat, the _Gitana_ (curve
E), and in the Pictet high speed vessel (curve B).

The _Gitana_ was tried with speeds varying between 0 and 4 kilometers.
The corresponding tractive stresses have been reduced to the same
transverse section as in the Pictet model in order to render the
observations comparable. At slight speeds, and up to 19.5 kilometers per
hour, the _Gitana_, which is the sharper, runs easier and requires a
slighter tractive stress. At such a speed there is an equality; but,
beyond this, the Pictet boat presents the greater advantages, and, at a
speed of 27 kilometers, requires a stress about half less than does the
_Gitana_. Such results explain themselves when we reflect that at these
great speeds the _Gitana_ sinks to such a degree that the afterside
planks are at the level of the water, while the Pictet model rises
simultaneously fore and aft, thus considerably diminishing the submerged
section.

With low or moderate speeds there is a perceptible equality between the
theoretic curve and the curve of the fast boat; but, starting from 16
kilometers, the stress diminishes. The greater does the speed become,
the more considerable is the diminution in stress; and, starting from a
certain speed, the rise of the boat is such as to diminish its absolute
tractive stress--a fact of prime importance established by theory and
confirmed by experiment.

The curves in Fig. 4 show the power in horses necessary to effect
progression at different speeds. The curve, A, has reference to an
ordinary boat that preserves its water lines constant, and the curve,
B, to a swift boat of the same tonnage. Up to 16 kilometers, the swift
vessel presents no advantage; but beyond that speed, the advantage
becomes marked, and, at a speed of 27 kilometers, the power to be
expended is no more than half that which corresponds to the same speed
for an ordinary boat.

The water escapes in a thin and even sheet as soon as the tractive
stress exceeds 2,000 kilogrammes; and the intensity and size of
the eddies from the boat sensibly diminish in measure as the speed
increases.

The interesting experiments made by Mr. Pictet seem, then to clearly
establish the fact that the forms deduced by calculation are favorable
to high speeds, and will permit of realizing, in the future, important
saving in the power expended, and, consequently, in the fuel (much less
of which will need to be carried), in order to perform a given passage
within a given length of time. Thus is explained the great interest that
attaches to Mr. Pictet's labors, and the desire that we have to soon be
able to make known the results obtained with such great speeds, not when
the boat is towed, but when its propulsion is effected through its
own helix actuated by its own engine, which, up to the present,
unfortunately, has through its defects been powerless to furnish the
necessary amount of power for the purpose.--_La Nature_.

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