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

V >> Various >> Scientific American Supplement, No. 385, May 19, 1883

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INITIAL STABILITY INDICATOR FOR SHIPS.

For a vessel with a given displacement, the metacenter and center of
gravity being known, it is easy to lay off in the form of a diagram
its stability or power of righting for any given angle of heel. Such a
diagram is shown in Fig. 3, in which the abscissae are the angles of the
heel, and the ordinates the various lengths of the levers, at the end
of which the whole weight of the vessel is acting to right itself.
The curve may be constructed in the following manner: Having found by
calculation the position of the transverse metacenter, M, for a given
displacement--Figs. 1 and 2--the metacentric height, G M, is then
determined either by calculations, or more correctly by experiment, by
varying the position of weights of known magnitude, or by the stability
indicator itself. Suppose, now, the vessel to be listed over to various
angles of heel--say 20 deg., 40 deg., 60 deg., and 80 deg.--the water
lines will then be A C, D E, F K, and H J respectively, and the centers
of buoyancy, which must be found by calculation, will be B1, B2, B3, and
B4. If lines are drawn from these points at right angles to the water
levels at the respective heels, the righting power of the vessel in each
position is found by taking the perpendicular distances between these
lines and the center of gravity, G. This method of construction is shown
to an enlarged scale in Fig. 2, where G is the center of gravity, B1
Z1, B2 Z2, B3 Z3, and B4 Z4 the lines from centers of buoyancy to water
levels; and G N, G O, and G P the distances showing the righting power
at the angles of 20 deg., 40 deg., and 60 deg. respectively, and which
to any convenient scale are set off as the ordinates in the stability
curve shown in Fig 3.

[Illustration: STABILITY INDICATOR FOR SHIPS. Fig. 1.]

Having obtained the curve, A, in this manner for a given metacentric
height, we will suppose that on the next voyage, with the same
displacement, it is found that, owing to some difference in stowage,
the center of gravity is 6 in. higher than before. The ordinates of the
curve will then be G N and G O--Fig.2--and the stability curve will
be as at C--Fig. 3--showing that at about 47 deg. all righting power
ceases. Similarly, if the center of gravity is lowered 6 in. on the
same displacement, the curve, B, will be found, and in this manner
comparative diagrams can be constructed giving at a glance the stability
of a vessel for any given draught of water and metacentric height.

[Illustration: STABILITY INDICATOR FOR SHIPS. Fig. 2.]

[Illustration: STABILITY INDICATOR FOR SHIPS. Fig. 3.]

The object of Mr. Alexander Taylor's indicator is to measure and show
by simple inspection the metacentric height under every condition of
loading, and therefore to make known the stability of the vessel. It
consists of a small reservoir, A, Fig. 4, placed at one side of the
ship, in the cabin, or other convenient locality, communicating by a
tube with the glass gauge, B, secured at the opposite side, the whole
being half filled with glycerine, which is the fluid recommended by Mr.
Wm. Denny, though water or any other liquid will answer the purpose.
At one side of the gauge is the circular scale, C, capable of being
revolved round its vertical axis, as well as adjusted up and down, so
as to bring the zero pointer exactly to the top of the fluid when the
vessel is without list. Round the top of the scale, at D, are engraved
four different draughts, and under these are the metacentric heights.
Test tanks of known capacity are placed at each side of the vessel, but
in no way connected with the reservoir or gauge. The metacentric height
is found as follows: The ship being freed from bilge water, the roller
scale is turned round to bring to the front the mark corresponding with
the mean draught of the vessel at the time, and the zero pointer is
placed opposite the surface of the liquid in the gauge. One of the test
tanks being filled with a known weight of water, the vessel is caused
to list, and in consequence the liquid in the tube takes a new position
corresponding with the degree of heel, the disturbance being greater
according as the vessel has been more or less overbalanced. The scale
having previously been properly graduated, the metacentric height for
the draught and state of loading can be at once read off in inches,
while as a check the water can be transferred from the one test tank to
the other, and the metacentric height read off as before, but on the
opposite side of the zero pointer. At the same time the angle of heel is
shown on a second graduated scale, E. Having obtained the metacentric
height, reference to a diagram will at once show the whole range of
stability; and this being ascertained at each loading, the stowage of
the cargo can be so adjusted as to avoid excessive stiffness in the one
hand and dangerous tenderness on the other. It will thus be seen that
Mr. Taylor's invention promises to be of great practical value both in
the hands of the ship-builder and ship-owner, who have now an instrument
placed before them, by the proper use of which all danger from
unskillful loading can be entirely avoided.--_The Engineer_.

[Illustration: STABILITY INDICATOR FOR SHIPS. Fig. 4.]

* * * * *

SCRIVANOW'S CHLORIDE OF SILVER PILE.

Considerable attention has been attracted lately at Paris among those
who are interested in electrical novelties to a chloride of silver
pile invented by Mr. Scrivanow. The experiments to which it has been
submitted are, in some respects, sufficiently extraordinary to cause us
to make them known to our readers, along with the inventor's description
of the apparatus.

Mr. Scrivanow's intention appears to be to apply this pile to the
lighting of apartments, and even to the running of small motors, and,
for the purpose of actuating sewing machines, he has already constructed
a small model whose external dimensions are 160 x 100 x 90 millimeters.

"My invention," says the inventor, "is intended as an electric pile
capable of regeneration. The annexed Fig. 1 shows a vertical arrangement
of the apparatus, and Fig. 2 a horizontal one. In the latter, two
elements are represented superposed.

"My pile consists of a prism of retort carbon (a) covered on every side
with pure chloride of silver (b). The carbon thus prepared is immersed
in a solution of hydrate of potassium (KHO) or of hydrate of sodium
(NaHO), marking 1.30 to 1.45 by the Baume areometer, the solvent being
water.

"In the vicinity of the carbon is arranged the plate to be attacked--a
plate of zinc (c) of good quality. The surface of the electrodes, and
their distance apart, depends upon the effects that it is desired to
obtain, and is determined in accordance with the well known principles
of electro-kinetics.

"The chemical reactions that take place in this couple are multiple.
In contact with a sufficiently concentrated solution of hydrate of
potassium or sodium, the chloride of silver, especially if it has been
recently prepared, passes partially into the state of brown or black
oxide, so that the carbon becomes covered, after remaining sufficiently
long in the exciting liquid, with a mixture of chloride and oxide of
silver. When the circuit is closed, the chloride becomes reduced to a
spongy metallic state and adheres to the surface of the carbon. At the
same time the zinc passes, in the alkaline solution, into a state of
chloride and of soluble combination of zinc oxide and of alkali.

"To avoid all loss of silver I cover the carbon with asbestos paper, or
with cloth of the same material, d. My piles are arranged in ebonite
vessels, A, which are flat, as in Fig. 1, or round, as in Fig. 2.

"In Fig 1 there is seen, at e, gutta-percha separating the zinc from the
carbon at the base.

"Under such conditions, we obtain a powerful couple that possesses an
electro-motive power of 1.5 to 1.8 volts, according to the concentration
of the exciting liquid. The internal resistance is extremely feeble. I
have obtained with piles arranged like those shown in the figures nearly
0.06 ohm, the measurements having been taken from a newly charged pile.

"When the element is used up, and, notably, when all the chloride of
silver is reduced, it is only necessary to plunge the carbon with its
asbestos covering (after washing it in water) into a chloridizing bath,
in order to bring back the metallic silver that invests the carbon to a
state of chloride, and thus restore the pile to its primitive energy.
After this the carbon is washed and put back into the exciting liquid.

"These reductions of the chloride of silver during the operation of the
pile can be reproduced _ad infinitum_, since they are accompanied by no
loss of metal. The alkaline liquid is sufficient in quantity for two
successive charges of the couple.

"The chloridizing bath consists of 100 parts of acetic acid, 5 to 6
parts, by weight, of hydrochloric acid, and about 30 parts of water.

[Illustration: FIG. 1.--SCRIVANOW'S CHLORIDE OF SILVER PILE.]

"Other acids may be employed equally as well. A bath composed of
chlorochromate of potassium and nitric or sulphuric acid makes an
excellent regenerator.

"To sum up, I claim as the distinctive characters of my pile:

"1. The use of the potassic or sodic alkaline liquid conjointly with
chloride of silver, and the oxide of the same, that forms through the
immersion of the carbon in a chloridizing bath.

"2. The use of retort or other carbon covered with the salt of silver
above specified.

"3. The arrangement and construction of my pile as I have described."

In the experiments recently tried with Mr. Scrivanow's pile, a large
sized battery was made use of, whose dimensions were 300 x 145 x 125
millimeters, and whose weight was from 5 to 6 kilogrammes. The results
were: intensity, 1 ampere; electro-motive power, 25 volts, corresponding
to an energy of 25 volt-amperes, or about 2.5 kilogrammeters per second.
The pile was covered with a copper jacket whose upper parts supported
two Swan lamps. Upon putting on the cover a contact was formed with the
electrodes, and it was possible by means of a commutator key with three
eccentrics to light or extinguish one of the lamps or both at once.
A single element would have sufficed to keep one Swan lamp of feeble
resistance lighted for 20 hours. Accepting the data given above and
the 20 hours' uninterrupted duration of the pile's operation the power
furnished by this large model is equal to 2.5 x 20 x 3,600 = 180,000
kilogrammeters.

[Illustration: FIG. 1.--SCRIVANOW'S CHLORIDE OF SILVER PILE.]

In our opinion, Mr. Scrivanow's pile is not adapted for industrial use
because of the expense of the silver and the frequent manipulations it
requires, but it has the advantage, however, of possessing, along with
its small size and little weight, a disposable energy of from 150,000
to 200,000 kilogrammeters utilizable at the will of the consumer and
securing to him a certain number of applications, either for lighting or
the production of power. It appears to us to be specially destined to
become a rival to the bichromate of potash pile for actuating electric
motors applied to the directing of balloons.--_Revue Industrielle_.

* * * * *

ON THE LUMINOSITY OF FLAME.

The light emitted from burning gases which burn with bright flame is
known to be a secondary phenomenon. It is the solid, or even liquid,
constituents separated out by the high temperature of combustion, and
rendered incandescent, that emit the light rays. Gases, on the other
hand, which produce no glowing solid or liquid particles during
combustion burn throughout with a weakly luminous flame of bluish or
other color, according to the kind of gas. Now, it is common to say,
merely, in explanation of this luminosity, that the gas highly heated in
combustion is self-incandescent. This explanation, however, has not been
experimentally confirmed. Dr Werner Siemens was, therefore, led recently
to investigate whether highly-heated pure gases really emit light.

The temperature employed in such experiments should, to be decisive,
be higher than those produced by luminous combustion. The author had
recourse to the regenerative furnace used by his brother, Friedrich, in
Dresden, in manufacture of hard glass. This stands in a separate room
which at night can be made perfectly dark. The furnace has, in the
middle of its longer sides, two opposite apertures, allowing free vision
through. It can be easily heated to the melting temperature of steel,
which is between 1,500 deg. and 2,000 deg. C. Before the furnace apertures were
placed a series of smoke blackened screens with central openings, which
enabled one to look through without receiving, on the eye, rays from the
furnace walls. If, now, all air exchange was prevented in the furnace,
and all light excluded from the room, it was found that not the least
light came to the eye from the highly-heated air in the furnace. For
success of the experiment, it was necessary to avoid any combustion in
the furnace, and to wait until the furnace-air was as free from dust as
possible. Any flame in the furnace (even when it did not reach into the
line of sight), and the least quantity of dust in it, illuminated the
field of vision.

As a result of these experiments, Dr. Siemens considers that the view
hitherto held, that highly-heated gases are self-luminous, is not
correct. In the furnace were the products of the previous combustion
and atmospheric air: consequently oxygen, nitrogen, carbonic acid, and
aqueous vapor. If even one of these gases was self-luminous, the field
of vision must have been always illuminated. The weak light given by
the flame of burning gases that separate out no solid nor liquid
constituents cannot, therefore, be explained as a phenomenon of glow of
the gaseous products.

It appealed to the author probable, that heated gases did not, either,
emit heat rays; and he set himself to test this idea, experimenting, in
company with Herr Froehlich, in Dresden. They first convinced themselves
in this case that the light emission of pure heated gases sunk to zero,
even when the field of vision was not always quite dark, and it was
only possible to observe this a short time; but the repeatedly observed
perfect darkness of the field of vision was demonstrative. On the other
hand, experiments made with sensitive thermopiles, in order to settle
the question of emission of heat-rays from highly-heated gases, failed.

Afterward, however, Dr. Siemens was convinced, by a quite simple
experiment of a different kind, that his supposition was erroneous. An
ordinary lamp, with circular wick, and short glass cylinder, was wholly
screened with a board, and a thermopile was so placed that its axis lay
somewhat higher than the edge of the board. As the room-walls had pretty
much a uniform temperature, the deflection of the galvanometer was but
slight, when the tube-axis of the thermopile was directed anywhere
outside of the hot-air current rising from the flame. When, however, the
axis was directed to this current, a deflection occurred, which was as
great as that from the luminous flame itself. That the heat radiation
from hot gases is but very small in comparison with that from equally
hot solid bodies, was shown by the large deflection produced when a
piece of fine wire was held in the hot-air current. On the other hand,
however, it was far too considerable to admit of being attributed to
dust particles suspended in the air current.

It must be conceded to be possible (the author says) that the light
radiation of hot gases, as also the heat radiation, is only exceedingly
weak, and therefore may escape observation. It is, therefore, much to
be desired that the experiments should be repeated at still higher
temperatures and with more exact instruments, in order to determine
the limit of temperature at which heated gases undoubtedly become
self-incandescent. The fact, however, that gases, at a temperature of
more than 1,500 deg. C, are not yet luminous, proves that the incandescence
of the flame is not to be explained as a self-incandescence of the
products of combustion. This is confirmed by the circumstance that, with
rapid mixture of the burning gases, the flame becomes shorter because
the combustion process goes on more quickly, and hotter because less
cold air has access. Further, the flame also becomes shorter and hotter
if the gases are strongly heated previous to combustion. As the rising
products of combustion still retain for a time the temperature of the
flame, the reverse must occur if the gases were self-luminous. The
luminosity of the flame, however, ceases at a sharp line of demarkation,
and evidently coincides with completion of the chemical action. The
latter, itself, therefore, and not the heating of the combustion
products, which is due to it, must be the cause of the luminosity. If
we suppose that the gas-molecules are surrounded by an ether-envelope,
then, in chemical combination of two or several such molecules, there
must occur a changed position of the ether-envelopes. The motion of
ether-particles thus caused may be represented by vibrations, which form
the starting-point of light and heat-waves.

In quite a similar manner we may also, according to Dr. Siemens,
represent the light-phenomenon occurring when an electric current
is sent through gases, which always takes place when the maximum of
polarization belonging to them is exceeded. As the passage of the
current through the gas seems to be always connected with chemical
action, the phenomenon of glow may be explained in the same way as in
flame, by oscillating transposition of the ether envelopes, by which the
passage of electricity is effected. In that case the light of flame may
be called electric light by the same light as the light of the ozone
tube or the Geissler tube, which is mainly to be distinguished from the
former in that it contains a dielectric of an extremely small maximum of
polarization. This correspondence in the causes of luminosity of flame,
and of gases traversed by electric currents, is supported by the
similarity of the flame-phenomena in strength and color of light.

[These researches were lately described by Dr. Werner Siemens to the
Berlin Academy.]

* * * * *

A QUICK WAY TO ASCERTAIN THE FOCUS OF A LENS.

It is well known that if the size of an object be ascertained, the
distance of a lens from that object, and the size of the image depicted
in a camera by that lens, a very simple calculation will give the
focus of the lens. In compound lenses the matter is complicated by the
relative foci of its constituents and their distance apart; but these
items, in an ordinary photographic objective, would so slightly affect
the result that for all practical purposes they may be ignored.

What we propose to do--what we have indeed done--is to make two of these
terms constant in connection with a diagram, here given, so that a mere
inspection may indicate, with its aid, the focus of a lens. All that is
required in making use of it is to plant the camera perfectly upright,
and place in front of it, at exactly fifteen feet from the center of the
lens, a two foot rule, also perfectly upright and with its center
the same height from the floor as the lens, and then, after focusing
accurately with as large a diaphragm as will give sharpness, to note the
size of the image and refer it to the diagram. The focus of the lens
employed will be marked under the line corresponding to the size of the
image of the rule on the ground glass.

As our object is to minimize time and trouble to the utmost, we may make
a suggestion or two as to carrying out the measuring. It will be obvious
that any object exactly two feet in length, rightly placed, will answer
quite as well as a "two-foot," which we selected as being about as
common a standard of length and as likely to be handy for use as
any. The pattern in a wall paper, a mark in a brick wall, a studio
background, or a couple of drawing pins pressed into a door, so long as
two feet exactly are indicated, will answer equally well.

And, further, as to the actual mode of measuring the image on the
ground glass (we may say that there is not the slightest need to take
a negative), it will perhaps be found the readiest method to turn the
glass the ground side outward, when two pencil marks may be made with
complete accuracy to register the length of the image, which can then be
compared with the diagram. Whatever plan is adopted, if the distance be
measured exactly between lens and rule, the result will give the focus
with exactitude sufficient for any practical purpose.--_Br. Jour. of
Photo_.

[Illustration]

* * * * *

THE HISTORY OF THE PIANOFORTE.

[Footnote: A paper recently read before the Society of Arts, London.]

By A. J. HIPKINS.

As this paper is composed from a technical point of view, some
elucidation of facts, forming the basis of it, is desirable before we
proceed to the chronological statement of the subject. These facts are
the strings, and their strain or tension; the sound-board, which is the
resonance factor; and the bridge, connecting it with the strings. The
strings, sound-board, and bridge are indispensable, and common to
all stringed instruments. The special fact appertaining to keyboard
instruments is the mechanical action interposed between the player and
the instrument itself. The strings, owing to the slender surface they
present to the air, are, however powerfully excited, scarcely audible.
To make them sufficiently audible, their pulsations have to be
communicated to a wider elastic surface, the sound-board, which, by
accumulated energy and broader contact with the air, re-enforces the
strings' feeble sound. The properties of a string set in periodic
vibration are the best known of the phenomena appertaining to acoustics.
The molecules composing the string are disturbed in the string's
vibrating length by the means used to excite the sound, and run off into
sections, the comparative length and number of which depend partly upon
the place in the string the excitement starts from; partly upon the
force and the form of force that is employed; and partly upon the
length, thickness, weight, strain, and elasticity of the string, with
some small allowance for gravitation. The vibrating sections are of
wave-like contour; the nodes or points of apparent rest being really
knots of the greatest pressure from crossing streams of molecules. Where
the pressure slackens, the sections rise into loops, the curves of which
show the points of least pressure. Now, if the string be struck upon a
loop, less energy is communicated to the string, and the carrying power
of the sound proportionately fails. If the string be struck upon a node,
greater energy ensues, and the carrying power proportionately gains.
By this we recognize the importance of the place of contact, or
striking-place of the hammer against the string; and the necessity, in
order to obtain good fundamental tone, which shall carry, of the note
being started from a node.

If the hammer is hard, and impelled with force, the string breaks into
shorter sections, and the discordant upper partials of the string, thus
brought into prominence, make the tone harsh. If the hammer is soft, and
the force employed is moderated, the harmonious partials of the longer
sections strike the ear, and the tone is full and round. By the
frequency of vibration, that is to say, the number of times a string
runs through its complete changes one way and the other, say, for
measurement, in a second of time, we determine the pitch, or relative
acuteness of the tone as distinguished by the ear.

We know, with less exactness, that the sound-board follows similar laws.
The formation of nodes is helped by the barring of the sound-board,
a ribbing crosswise to the grain of the wood, which promotes the
elasticity, and has been called the "soul" of stringed musical
instruments. The sound-board itself is made of most carefully chosen
pine; in Europe of the _Abies excelsa_, the spruce fir, which, when well
grown, and of light, even grain, is the best of all woods for resonance.
The pulsations of the strings are communicated to the sound-board by the
bridge, a thick rail of close-grained beech, curved so as to determine
their vibrating lengths, and attached to the sound-board by dowels. The
bridge is doubly pinned, so as to cut off the vibration at the edge
of the bearing the strings exert upon the bridge. The shock of each
separate pulsation, in its complex form, is received by the bridge,
and communicated to such undamped strings as may, by their lengths, be
sensitive to them; thus producing the AEolian tone commonly known as
sympathetic, an eminently attractive charm in the tone of a pianoforte.

We have here strings, bridge, and sound-board, or belly, as it is
technically called, indispensable for the production of the tone, and
indivisible in the general effect. The proportionate weight of
stringing has to be met by a proportionate thickness and barring of the
sound-board, and a proportionate thickness and elevation of the bridge.

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