Scientific American Supplement, No. 447, July 26, 1884

V >> Various >> Scientific American Supplement, No. 447, July 26, 1884

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They, however, led Mr. Munro to proceed with compound wire structures,
such as gratings resting upon or rubbing against one another, and one of
the first experiments in this direction proved very successful, and led
Mr. Munro to the construction of his gauze telephone, which is the most
characteristic and efficient of his practical apparatus.

This instrument consists essentially of two pieces of iron-wire gauze,
the one fixed in a vertical plane, and the other resting more or less
lightly against it, the pressure between them being regulated by an
adjustable spring or weight. These gauze plates are so connected in a
telephonic circuit as to constitute the electrodes of a microphone; for
touching one another lightly in several points, they allow the current
to be transmitted between them in inverse proportion to the resistance
offered to it in its passage from one to the other. Under the influence
of sonorous vibrations the one plate dances more or less on the other,
thus varying the resistance; and very perfect articulation is produced
in a telephonic receiver included in the circuit. The gauze transmitter
so constructed may be fixed within a wall-box with or without a
mouthpiece; but as the sound waves acting directly upon the gauze plates
set them into agitation through their sympathetic vibration or by direct
impact, no sort of diaphragm or equivalent device is necessary, and none
is employed.

[Illustration: FIG. 1.]

A convenient form of this apparatus is shown in Fig. 1, and to which the
name of "The Lyre Telephone" has been given from its resemblance to that
impossible musical instrument. In this apparatus, G is a plate of iron
wire gauze stretched vertically between two horizontal wires attached to
a lyre-shaped framework of mahogany; against the plate rests the smaller
plate, G squared, the normal pressure between them being regulated by an
adjustable spring acting in opposition to a weighted lever, W. The two
plates are connected respectively with the attachment screws, X and
Y, by which the instrument is placed in a circuit with a battery and
telephonic circuit.

[Illustration: FIG. 2.]

A modification of this apparatus is shown in the diagram sketch, Fig.
2, which will probably be a more practical form. In this instrument the
electrodes consist of two circular disks of iron wire gauze of different
diameters, the larger disk, G, which is fixed, being pierced with holes
of smaller diameter than the smaller disk, G squared. In the diagram the two
disks are shown separated for the purpose of explanation, but in reality
they rest the one against the other; the smaller and movable disk,
G squared, is held up against G with greater or less pressure by the spiral
spring, S, the tension of which can be adjusted by a screw or other
suitable device at N. This form of the apparatus is more suitable for
inclosure in a wall box with or without a mouthpiece, but it does not
require the employment of any kind of diaphragm or tympan. Mr. Munro
can employ with all his instruments an induction coil for installations
where the resistance of the line wire makes it desirable to do so; the
microphone and battery being included in the primary circuit and the
telephones in the secondary.

[Illustration: FIG. 3.]

Fig. 3 is an ingenious arrangement devised by Mr. Munro, in which the
adjusting spring or weight is substituted by a magnet which may be
either a permanent or an electro-magnet. The figure shows an arrangement
in which the fixed gauze, g, is perforated as in the apparatus
illustrated in Fig. 2, and the movable electrode, g, is bent or dished
so as to press upon g around its edge. E is a magnet which by its
attractive influence upon g holds t up against g with a pressure
dependent upon its magnetic intensity and upon its distance from the
gauze. By making E an electro-magnet, and including its coil in the
telephonic circuit, an instrument may be constructed in which the normal
pressure between the electrodes can be automatically adjusted to the
strength of the current, and in cases where an induction coil is
employed the magnet, E, may be the core of such a coil.

[Illustration: FIG. 4.]

Fig. 4 illustrates an apparatus devised by Mr. Munro, and to which the
name thermo-microphone might be given, as it is a microphone in which
thermo-electric currents are employed in the place of voltaic currents,
its special feature of interest lying in the fact that the heated
junction of the thermo-electric couple is identical with the microphone
contacts of the two electrodes. In this very elegant experiment a piece
of iron wire gauze, G, is supported in a horizontal position by a light
metallic support, B. To another support. A, is loosely hinged a frame,
which at its further extremity carries a little coil of German silver
wire, C, which by its weight rests upon the center of the gauze plate,
G; and in contact therewith, and to increase the pressure of contact, a
little bar weight is laid within the convolutions of the core. The
two electrodes, the gauze, and the coil are connected, as shown, to a
receiving telephone, T. Upon the application of heat, as from the flame
of a spirit lamp placed below, a thermo-electric current is set up
throughout the circuit; in this condition the apparatus becomes a very
perfect microphone, and when the pressure between the electrodes is
properly adjusted it is a very efficient telephonic transmitter,
transmitting articulate speech and musical sounds with remarkable
clearness and fidelity.

[Illustration: FIG. 5]

Mr. Munro is, with the aid of Mr. Warwick's manipulative skill,
extending this portion of his investigation further by experimenting
with gauzes and coils of various metals forming other couples in
the thermo-electric series, as well as with iron and other gauzes
electrotyped with bismuth and other metals, and we hope in due time to
lay the results of those experiments before our readers.

Mr. Munro has, moreover, observed that if two pieces of gauze of
identical material and in microphonic contact be heated, a peculiar
sighing sound is heard in a telephone connected with them and with a
battery, and he attributes this phenomenon to the electrical discharge
between the gauze plates being facilitated and increased by the
action of heat, but we are rather inclined to trace the effect to the
mechanical action of the one gauze moving over the other under the
influence of expansion and contraction of the metals by the variable
temperature of the flame and convection currents of heated air, such
movement producing the sounds just as would be produced if one of the
electrodes of an ordinary microphone were as delicately moved by the
hand or other agent.

[Illustration: FIG. 6]

Figs. 5 and 6 illustrate another and distinct form of metallic
microphone transmitter designed by Mr. Munro and Mr. Warwick, in which
a small chain, preferably of iron, forms the microphonic portion of the
apparatus. In Fig. 5, A is a plate of sonorous wood forming a diaphragm
or collector of the sonorous waves; to the back of this is attached a
short length of chain, C, the opposite ends of which are by the wires, X
and Y, included in the telephonic circuit. The points of junction of the
links with one another constitute the variable microphonic contacts, and
the normal pressure between them is adjusted by the spiral spring, S,
the tension of which may be varied by the cord and winding pin, B. Fig.
6 is the section of a transmitter constructed upon this principle, and
in which two chains, c and c', are employed attached at one end by a
wire, f, to a diaphragm mouthpiece, N, and at their opposite extremities
to the adjusting springs, s and s'; an induction coil, D, may be
employed if the resistance of the line render it advantageous.

[Illustration: FIG. 7]

Fig. 7 is a form of pencil microphone experimented with by Mr. Munro,
which differs from some of the Hughes' transmitters adopted by Crossley,
Gower, Ader, and many others only in the material of which it is
composed, Mr. Munro's being of cast iron, while the others to which we
have referred are of carbon rods such as are used in electric lighting.
In Fig. 7 a light cast-iron bar, i squared, of the form shown, is supported in
holes drilled in two blocks of cast iron, i i', and the pressure between
the bar and the blocks can be adjusted by a regulating spring, s. In
connection with this apparatus Mr. Munro has observed that rust has no
appreciable effect upon the efficiency of the instrument unless it be
to such an extent as to cause the two to adhere, or to be "rusted up"
together.

[Illustration: FIG. 8]

We now come to another class of metallic transmitters with which Mr.
Munro and his associate have been making experiments, and to which he
has given the name "Grain transmitter," since it consists of a box
having metallic sides, e e', to which terminal screws, t t', are
attached and filled in between with iron or brass filings, granules of
spongy iron, or indeed small metallic particles in any form; one of the
most efficient transmitters being a box such as is shown in Fig. 8,
filled with a quantity of 1/4 in. screws.

[Illustration: FIG. 9]

The results of Mr. Munro's experiments have led him to the opinion
that the action of the microphone must be attributed to the action
of sonorous vibrations upon the air or gaseous medium separating the
so-called contact-points of the electrodes, and that across these
spaces, or films of gaseous matter, silent electrical discharges take
place, the strengths of which, being determined by the thickness of the
gaseous strata through which they pass, vary with the motion of the
electrodes; and as, according to this hypothesis, the distances of the
electrodes from one another is determined by the sound-waves, the sound
in that way controls the current.--_Engineering_.

* * * * *

APPARATUS FOR MANEUVRING BICHROMATE OF POTASSA PILES FROM A DISTANCE.

Bichromate of potassa piles, especially those single liquid ones that
are applied to domestic lighting, all present the grave defect of
consuming almost as much zinc in open as in closed circuit, and of
becoming rapidly exhausted if care be not taken to remove the zinc from
the liquid when the battery is not in use. This operation, which is a
purely mechanical one, has hitherto required the pile to be located near
the place where it was to be used, or to have at one's disposal a system
of mechanical transmission that was complicated and not very ornamental.

In order to do away with this inconvenience, which is inherent to all
bichromate piles, Mr. G. Mareschal has invented and had constructed an
ingenious system that we shall now describe.

[Illustration: FIG. 1.--BICHROMATE OF POTASSIUM PILE, WITH MANEUVERING
APPARATUS.]

Mr. Mareschal's plan consists in suspending the frame that carries all
the battery zincs (Fig. 1) from the extremity of a horizontal beam, and
balancing them by means of weights at the other extremity.

The system, being balanced, the lifting or immersion of the zincs then
only requires a slight mechanical power, such as may be obtained from
an ordinary kitchen jack through a combination that will be readily
understood upon reference to Fig. 2. The axis, M, of the jack,
on revolving, carries along a crank, MD, to which is fixed a
connecting-rod, A, whose other extremity is attached to the horizontal
beam that supports the zincs and counterpoises. If the axle, M, be given
a continuous revolution, it will communicate to the rod, A, an upward
and downward motion that will be transmitted to the beam and produce an
alternate immersion and emersion of the zincs.

Upon stopping the jack at certain properly selected positions of the
rod, MD, the zincs may, at will, be kept immersed in the liquids, or
_vice versa_. This is brought about by Mr. Mareschal in the following
way: The jack carries along in its motion a horizontal fly-wheel, V,
against whose rim there bears an iron shoe, F, placed opposite an
electro-magnet, E. In the ordinary position, this shoe, which is fixed
to a spring, bears against the felly of the wheel and stops the jack
through friction. When a current is sent into the electro-magnet, E, the
brake shoe, F, is attracted, leaves the fly wheel, and sets free the
jack, which continues to revolve until the current ceases to pass into
the electro.

[Illustration: FIG. 2.--PRINCIPLE OF THE APPARATUS.]

The problem, then, is reduced to sending a current into the electro and
in shutting it off at the proper moment. This result is obtained very
simply by means of an auxiliary Leclauche pile. (The piles got up for
house bells will answer.) The current from this pile is cut off from
the electro, F, by means of a button, B, when it is desired to light or
extinguish the lamps. In a position of rest, for example, the crank, MD,
is vertical, as shown in the diagram to the right in Fig. 2. The circuit
is open between M and N through the effect of the small rod, C, which
separates the spring, R, from the spring, R'. As soon as the circuit has
been closed, be it only for an instant, the crank leaves its vertical
position, the rod, C, quits the bend, S, and the spring, R, by virtue of
its elasticity, touches the spring, R', and continues its contact until
the crank, MD, having made a half revolution, the rod, C', repulses the
spring, R, and breaks the circuit anew. The brake then acts, and the
crank stops after making a revolution of 180 deg., and immersing the
zincs to a maximum depth. In order to extinguish the lamp, it is only
necessary to press the button, B, again. The axle, M, will then make
another half revolution, and, when it stops, the zinks will be entirely
out of the liquid. The depth of immersion is regulated by fixing the
crank-pin. D, in the apertures, T1, or T2, of the connecting rod. This
permits the travel, and consequently the degree of immersion, to be
varied.

The device requires three wires, two for connecting the lamp with the
battery, and one for maneuvering the apparatus through a closing of the
contact, B.

With Mr. Mareschal's system, bichromate of potassa piles may be utilized
in a large number of cases where a light of but short duration is
required until the battery is exhausted, without the tedious maneuvering
of a winch and without inconvenience. The jack permits of a large number
of lightings and extinctions being effected before it becomes necessary
to wind up its clockwork movement. This operation, however, is very
simple, and may be performed every time the battery is visited in order
to see what state it is in.

We regard Mr. Mareschal's apparatus as an indispensable addition to
every case of domestic electric lighting in which bichromate of potassa
piles are used, and, in general, to all cases where the pile becomes
uselessly exhausted in open circuit. It will likewise find an
application in laboratories, where the bichromate pile is in much demand
because of its powerful qualities, and where it is often necessary to
order it from quite a distant point.--_La Nature_.

* * * * *

MAGNETIC ROTATIONS.

By E. L. VOICE.

The remarkable researches and experiments of Professor Hughes clearly
show that magnetism is totally independent of iron, and that its
molecules, particles, or polarities are capable of rotation in that
metal. It would also appear that by reason of the friction between
magnetism and iron, the molecules of the latter are only partially
moved, such movement being the result of the tendency of iron to retard
magnetic change.

I have found that the magnetic molecules also possess inertia, that they
are capable of acquiring momentum, and that their rotation continues
for a considerable time after the exciting cause of their rotation has
ceased.

These facts may be proved in a very evident manner, inasmuch as induced
electric currents are generated by this _after_ rotation, which may be
made to light incandescent lamps.

In this case the magnetic rotations are produced in an electro magnet by
means of alternate currents supplied by alternating Gramme machine.

In order to better explain the action, it will be necessary to refer
to a new electro-motor, which was the subject of an article in the
_Electrical Review_ of February 19 last. It is of that type of motor in
which the field magnet and armature poles are alternately arranged, and
which requires a periodical reversibility of magnetism in the armature
to cause the latter to revolve, as in the Griscom motor. The insulating
strips in the commutator are sufficiently wide to demagnetize the whole
of the machine before reversibility in the armature takes place, and
this demagnetization sets up a _direct_ induced current, which is caught
in a shunt circuit by the aid of a second commutator, which only comes
into action when the first commutator goes out.

When this motor is supplied by a continuous current, it is easy to
understand that the induced current which passes through the shunt
circuit, and which is caused by the demagnetization, is proportional
to the mass of iron and wire of which the machine is composed, or
proportional to its inductive capacity. This current is purely a
secondary effect, of short duration, and only occurs once at each break
of the commutator.

The motor is of such a size that when supplied with a continuous current
of proper strength the induced electrical effect in the shunt circuit
will light one incandescent lamp. If, however, it is supplied with an
alternating current of the same power, it will light eight lamps, and
the mechanical power given off is even more than with a continuous
current, provided that the alternations from the dynamo do not exceed
6,000 a minute.

At first I was considerably puzzled by this great difference, because in
both cases it is impossible for the lamp circuit to be acted upon by the
main current. It occurred to me, however, that the rapid alternations
of the exciting current from the dynamo, and the consequent speed of
magnetic molecular rotation, gave the latter a certain momentum, and
that by widening the insulating strips of the first or main current
commutator, and proportionately increasing the width of conducting
surface in the shunt commutator up to certain limits, this effect would
be increased. I found such to be the case, from which I inferred that
the increase of induced current in the shunt circuit was on account of
its longer duration, by reason of the acquired momentum of the magnetic
molecular rotations _after_ the alternating exciting current had ceased.

[Illustration]

Those who have facilities for carrying out experiments may prove it in
the following manner:

E, in the inclosed drawing, is an electro-magnet whose brushes press on
two metallic bands, B and B, fixed to but insulated from the spindle,
A. The band, B, is in electrical circuit with the shunt commutator, S,
and the main commutator, M; while the band, B, is in contact with
shunt commutator, S, and main commutator, M. This contact is made
by conducting rods, as indicated. The commutators, as regards their
brushes, are so arranged that when M and M are in action, S and S are
out of action, and _vice versa_. The spindle and commutators are rotated
by the pulley, P. L is an incandescent lamp in the shunt circuit.

Let us now suppose the apparatus at rest, and the brushes in electrical
contact with the main commutators, M and M. The current from an
alternating dynamo passes into the magnet, E, and rapidly reverses its
polarity. By actuating the pulley, P, the commutators are rotated, when
M and M go out of, and the shunt commutators, S and S, come into
action, enabling the _after_ current set up in the magnet to light the
lamp, L, in the shunt circuit.

In order to make comparative tests, the same apparatus may be supplied
with continuous instead of alternating currents. The after current in
the former case, however, is much smaller, consisting of one electrical
impulse only at each break of the commutator, whereas in the alternating
system these impulses are practically continued; the result being that,
all things being equal, a far greater number of lamps may be used in the
shunt than when supplied by continuous current only, and it would
appear that this difference can only be attributed to the fact that the
rotatory motion of magnetic molecules, or polarity of the magnet, E,
acquires momentum when acted upon by a suitable physical cause, such as
alternating currents of electricity; this momentum lasting a sensible
time after the cessation of the acting cause.

If we had the gift of magnetic sight, and could see what is going on in
the electro-magnet when it is excited by alternating currents, we should
probably see the molecules or polarities tumbling over each other at an
enormous rate. I do not think, however, that we should see anything but
a vibratory motion as regards the iron molecules.--_Elec. Review_.

* * * * *

[AMER. MICROSCOP. JOUR.]

LIGHTON'S IMMERSION ILLUMINATOR

The following extremely simple plan for an immersion illuminator was
first brought to the notice of microscopists a few years ago, and,
in the absence of the inventor, was kindly described by Prof. Albert
McCalla, at the meeting of the American Society of Microscopists, at
Columbus, O. It consists of a small disk of silvered plate glass, c,
about one-eighth of an inch thick, which is cemented by glycerine
or some homogeneous immersion medium to the under surface of the
glass-slide, s. Let r represent the silvered surface of the glass disk,
b, the immersion objective, f, the thin glass cover. It will be easily
seen that the ray of light, h, from the mirror or condenser above the
stage will enter the slide and thence be refracted to the silvered
surface of the illuminator, r, whence it is reflected at a corresponding
angle to the object in the focus of the objective. A shield to prevent
unnecessary light from entering the objective can be made of any
material at hand, by taking a strip one inch long and three-fourths
of an inch wide and turning up one end. A hole not more than
three-sixteenths of an inch in diameter should be made at the angle. The
shield should be placed on the upper surface of the slide, so that the
hole will cover the point where the light from the mirror enters the
glass. With this illuminator Moeller's balsam test-plate is resolved
with ease, with suitable objectives. Diatoms mounted dry are shown in
a manner far surpassing that by the usual arrangement of mirror,
particularly with large angle dry objectives.

Ottumwa, Ia.

WM. LIGHTON.

[Illustration: LIGHTON'S ILLUMINATOR.]

* * * * *

FOUCAULT'S PENDULUM EXPERIMENTS.

By RICHARD A. PROCTOR.

Science owes to M. Foucault the suggestion that the motions of a
pendulum so suspended as to be free to swing in any vertical plane
might be made to give ocular demonstration of the earth's rotation. The
principle of proof may be easily exhibited, though, like nearly all of
the evidences of the earth's rotation, the complete theory of the
matter can only be mastered by the aid of mathematical researches of
considerable complexity. Suppose A B (Fig. 1) to be a straight rod in a
horizontal position bearing the free pendulum C D suspended in some such
manner as is indicated at C; and suppose the pendulum to be set swinging
in the direction of the length of the rod A B, so that the bob D remains
throughout the oscillations vertically under the rod A B. Now, if A B be
shifted in the manner indicated by the arrows, its horizontality being
preserved, it will be found that the pendulum does not partake in this
motion. Thus, if the direction of A B was north and south at first, so
that the pendulum was set swinging in a north and south direction, it
will be found that, the pendulum will still swing in that direction,
even though the rod be made to take up an east and west position.

[Illustration: Fig. 1.]

Nor will it matter if we suppose B (say) fixed and the rod shifted by
moving the end A horizontally round B. Further, as this is true whatever
the length of the rod, it is clear that the same fixity of the plane
of swing will be observed if the rod be shifted horizontally as though
forming part of a radial line from a point E in its length. In these
cases the plane of the pendulum's swing will indeed be shifted _bodily_,
but the direction of swing will still continue to be from north to
south.

Now, let P O P' represent the polar axis of the earth; a b a horizontal
rod at the pole bearing a pendulum, as in Fig. 1. It is clear that if
the earth is rotating about P O P' in the direction shown by the arrow,
the rod a b is being shifted round, precisely as in the case first
considered. The swinging pendulum below it will not partake in its
motion; and thus, through whatever arc the earth rotates from west to
east, through the same arc will the plane of swing of the pendulum
appear to travel from east to west under a b.

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