Scientific American Supplement, Vol. XXI., No. 531, March 6, 1886 by Various
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Various >> Scientific American Supplement, Vol. XXI., No. 531, March 6, 1886
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APPARATUS FOR DEMONSTRATING THAT ELECTRICITY DEVELOPS ONLY ON THE
SURFACE OF CONDUCTORS.
Mr. K.L. Bauer, of Carlsruhe, has just constructed a very simple and
ingenious apparatus which permits of demonstrating that electricity
develops only on the surface of conductors. It consists (see figure)
essentially of a yellow-metal disk, M, fixed to an insulating support,
F, and carrying a concentric disk of ebonite, H. This latter receives a
hollow and closed hemisphere, J, of yellow metal, whose base has a
smaller diameter than that of the disk, H, and is perfectly insulated by
the latter. Another yellow-metal hemisphere, S, open below, is connected
with an insulating handle, G. The basal diameter of this second
hemisphere is such that when the latter is placed over J its edge rests
upon the lower disk, M. These various pieces being supposed placed as
shown in the figure, the shell, S, forms with the disk, M, a hollow,
closed hemisphere that imprisons the hemisphere, J, which is likewise
hollow and closed, and perfectly insulated from the former.
[Illustration]
The shell, S, is provided internally with a curved yellow-metal spring,
whose point of attachment is at B, and whose free extremity is connected
with an ebonite button, K, which projects from the shell, S. By pressing
this button, a contact may be established between the external
hemisphere (formed of the pieces, S and M), and the internal one, J. As
soon as the button is left to itself, the spring again begins to bear
against the interior surface of S, and the two hemispheres are again
insulated.
The experiment is performed in this wise: The shell, S, is removed. Then
a disk of steatite affixed to an insulating handle is rubbed for a few
instants with a fox's "brush," and held near J until a spark occurs.
Then the apparatus is grasped by the support, F, and an elder-pith ball
suspended by a flaxen thread from a good conducting support is brought
near J. The ball will be quickly repelled, and care must be taken that
it does not come into contact with J. After this the apparatus is placed
upon a table, the shell, S, is taken by its handle, G, and placed in the
position shown in the figure, and a momentary contact is established
between the two hemispheres by pressing the button, K. Then the shell,
S, is lifted, and the disk, M, is touched at the same time with the
other hand. If, now, the pith ball be brought near S, it will be quickly
repelled, while it will remain stationary if it be brought near J, thus
proving that all the electricity passed from J to S at the moment of
contact.--_La Lumiere Electrique_.
* * * * *
THE COLSON TELEPHONE.
This apparatus has recently been the object of some experiments which
resulted in its being finally adopted in the army. We think that our
readers will read a description of it with interest. Its mode of
construction is based upon a theoretic conception of the lines of force,
which its inventor explains as follows in his Elementary Treatise on
Electricity:
"To every position of the disk of a magnetic telephone with respect to
the poles of the magnet there corresponds a certain distribution of the
lines of force, which latter shift themselves when the disk is
vibrating. If the bobbin be met by these lines in motion, there will
develop in its wire a difference of potential that, according to
Faraday's law, will be proportional to their number. All things equal,
then, a telephone transmitter will be so much the more potent in
proportion as the lines set in motion by the vibrations of the disk and
meeting the bobbin wire are greater in number. In like manner, a
receiver will be so much the more potent in proportion as the lines of
force, set in motion by variations in the induced currents that are
traversing the bobbin and meeting the disk, are more numerous. It will
consequently be seen that, generally speaking, it is well to send as
large a number of lines of force as possible through the bobbin."
[Illustration: FIG. 1.--THE COLSON TELEPHONE.]
In order to obtain such a result, the thin tin-plate disk has to be
placed between the two poles of the magnet. The pole that carries the
fine wire bobbin acts at one side and in the center of the disk, while
the other is expanded at the extremity and acts upon the edge and the
other side. This pole is separated from the disk by a copper washer, and
the disk is thus wholly immersed in the magnetic field, and is traversed
by the lines of force radiatingly.
This telephone is being constructed by Mr. De Branville, with the
greatest care, in the form of a transmitter (Fig. 2) and receiver (Fig.
3). At A may be seen the magnet with its central pole, P, and its
eccentric one, P'. This latter traverses the vibrating disk, M, through
a rubber-lined aperture and connects with the soft iron ring, F, that
forms the polar expansion. These pieces are inclosed in a nickelized
copper box provided with a screw cap, C. The resistance of both the
receiver and transmitter bobbin is 200 ohms.
[Illustration: FIG. 2.--TRANSMITTER TAKEN APART.]
The transmitter is 31/2 in. in diameter, and is provided with a
re-enforcing mouthpiece. It is regulated by means of a screw which is
fixed in the bottom of the box, and which permits of varying the
distance between the disk and the core that forms the central pole of
the magnet. The regulation, when once effected, lasts indefinitely. The
regulation of the receiver, which is but 21/4 in. in diameter, is
performed once for all by the manufacturer. One of the advantages of
this telephone is that its regulation is permanent. Besides this, it
possesses remarkable power and clearness, and is accompanied with no
snuffling sounds, a fact doubtless owing to all the molecules of the
disk being immersed in the magnetic field, and to the actions of the two
poles occurring concentrically with the disk. As we have above said,
this apparatus is beginning to be appreciated, and has already been the
object of several applications in the army. The transmitter is used by
the artillery service in the organization of observatories from which to
watch firing, and the receiver is added to the apparatus pertaining to
military telegraphy. The two small receivers are held to the lens of the
operator by the latter's hat strap, while the transmitter is suspended
in a case supported by straps, with the mouthpieces near the face (Fig.
1).
In the figure, the case is represented as open, so as to show the
transmitter. The empty compartment below is designed for the reception
and carriage of the receivers, straps, and flexible cords. This
arrangement permits of calling without the aid of special apparatus, and
it has also the advantage of giving entire freedom to the man on
observation, this being something that is indispensable in a large
number of cases.
[Illustration: FIG. 3.--RECEIVER TAKEN APART.]
In certain applications, of course, the receivers may be combined with a
microphone; yet on an aerial as well as on a subterranean line the
transmitter produces effects which, as regards intensity and clearness,
are comparable with those of a pile transmitter.
Stations wholly magnetic may be established by adding to the transmitter
and two receivers a Sieur phonic call, which will actuate them
powerfully, and cause them to produce a noise loud enough for a call. It
would be interesting to try this telephone on a city line, and to a
great distance on those telegraph lines that are provided with the Van
Rysselberghe system. Excellent results would certainly be obtained, for,
as we have recently been enabled to ascertain, the voice has a
remarkable intensity in this telephone, while at the same time perfectly
preserving its quality.--_La Nature_.
* * * * *
[NATURE.]
THE MELDOMETER.
The apparatus which I propose to call by the above name
([mu][epsilon][lambda][delta][omega], to melt) consists of an adjunct to
the mineralogical microscope, whereby the melting-points of minerals may
be compared or approximately determined and their behavior watched at
high temperatures either alone or in the presence of reagents.
As I now use it, it consists of a narrow ribbon of platinum (2 mm. wide)
arranged to traverse the field of the microscope. The ribbon, clamped in
two brass clamps so as to be readily renewable, passes bridgewise over a
little scooped-out hollow in a disk of ebony (4 cm. diam.). The clamps
also take wires from a battery (3 Groves cells); and an adjustable
resistance being placed in circuit, the strip can be thus raised in
temperature up to the melting-point of platinum.
The disk being placed on the stage of the microscope the platinum strip
is brought into the field of a 1" objective, protected by a glass slip
from the radiant heat. The observer is sheltered from the intense light
at high temperatures by a wedge of tinted glass, which further can be
used in photometrically estimating the temperature by using it to obtain
extinction of the field. Once for all approximate estimations of the
temperature of the field might be made in terms of the resistance of the
platinum strip, the variation of such resistance with rise of
temperature being known. Such observations being made on a suitably
protected strip might be compared with the wedge readings, the latter
being then used for ready determinations. Want of time has hindered me
from making such observations up to this.
The mineral to be experimented on is placed in small fragments near the
center of the platinum ribbon, and closely watched while the current is
increased, till the melting-point of the substance is apparent. Up to
the present I have only used it comparatively, laying fragments of
different fusibilities near the specimen. In this way I have melted
beryl, orthoclase, and quartz. I was much surprised to find the last
mineral melt below the melting-point of platinum. I have, however, by me
as I write, a fragment, formerly clear rock-crystal, so completely fused
that between crossed Nicols it behaves as if an amorphous body, save in
the very center where a speck of flashing color reveals the remains of
molecular symmetry. Bubbles have formed in the surrounding glass.
Orthoclase becomes a clear glass filled with bubbles: at a lower
temperature beryl behaves in the same way.
Topaz whitens to a milky glass--apparently decomposing, throwing out
filmy threads of clear glass and bubbles of glass which break,
liberating a gas (fluorine?) which, attacking the white-hot platinum,
causes rings of color to appear round the specimen. I have now been
using the apparatus for nearly a month, and in its earliest days it led
me right in the diagnosis of a microscopical mineral, iolite, not before
found in our Irish granite, I think. The unlooked-for characters of the
mineral, coupled with the extreme minuteness of the crystals, led me
previously astray, until my meldometer fixed its fusibility for me as
far above the suspected bodies.
Carbon slips were at first used, as I was unaware of the capabilities of
platinum.
A form of the apparatus adapted, at Prof. Fitzgerald's suggestion, to
fit into the lantern for projection on the screen has been made for me
by Yeates. In this form the heated conductor passes both below and above
the specimen, which is regarded from a horizontal direction.
J. JOLY.
Physical Laboratory, Trinity College, Dublin.
* * * * *
[AMERICAN ANNALS OF THE DEAF AND DUMB.]
TOUCH TRANSMISSION BY ELECTRICITY IN THE EDUCATION OF DEAF-MUTES.
Progress in electrical science is daily causing the world to open its
eyes in wonder and the scientist to enlarge his hopes for yet greater
achievements. The practical uses to which this subtile fluid,
electricity, is being put are causing changes to be made in time-tested
methods of doing things in domestic, scientific, and business circles,
and the time has passed when startling propositions to accomplish this
or that by the assistance of electricity are dismissed with incredulous
smiles. This being the case, no surprise need follow the announcement of
a device to facilitate the imparting of instruction to deaf children
which calls into requisition some service from electricity.
The sense of touch is the direct medium contemplated, and it is intended
to convey, with accuracy and rapidity, messages from the operator (the
teacher) to the whole class simultaneously by electrical
transmission.[1]
[Footnote 1: By the same means two deaf-mutes, miles apart, might
converse with each other, and the greatest difficulty in the way of a
deaf-mute becoming a telegraph operator, that of receiving messages,
would be removed. The latter possibilities are incidentally mentioned
merely as of scientific interest, and not because of their immediate
practical value. The first mentioned use to which the device may be
applied is the one considered by the writer as possibly of practical
value, the consideration of which suggested the appliance to him.]
An alphabet is formed upon the palm of the left hand and the inner side
of the fingers, as shown by the accompanying cut, which, to those
becoming familiar with it, requires but a touch upon a certain point of
the hand to indicate a certain letter of the alphabet.
A rapid succession of touches upon various points of the hand is all
that is necessary in spelling a sentence. The left hand is the one upon
which the imaginary alphabet is formed, merely to leave the right hand
free to operate without change of position when two persons only are
conversing face to face.
The formation of the alphabet here figured is on the same principle as
one invented by George Dalgarno, a Scottish schoolmaster, in the year
1680, a cut of which maybe seen on page 19 of vol. ix. of the _Annals_,
accompanying the reprint of a work entitled "_Didascalocophus_."
Dalgarno's idea could only have been an alphabet to be used in
conversation between two persons _tete a tete_, and--except to a limited
extent in the Horace Mann School and in Professor Bell's teaching--has
not come into service in the instruction of deaf-mutes or as a means of
conversation. There seems to have been no special design or system in
the arrangement of the alphabet into groups of letters oftenest
appearing together, and in several instances the proximity would
seriously interfere with distinct spelling; for instance, the group "u,"
"y," "g," is formed upon the extreme joint of the little finger. The
slight discoverable system that seems to attach to his arrangement of
the letters is the placing of the vowels in order upon the points of the
fingers successively, beginning with the thumb, intended, as we suppose,
to be of mnemonic assistance to the learner. Such assistance is hardly
necessary, as a pupil will learn one arrangement about as rapidly as
another. If any arrangement has advantage over another, we consider it
the one which has so grouped the letters as to admit of an increased
rapidity of manipulation. The arrangement of the above alphabet, it is
believed, does admit of this. Yet it is not claimed that it is as
perfect as the test of actual use may yet make it. Improvements in the
arrangement will, doubtless, suggest themselves, when the alterations
can be made with little need of affecting the principle.
In order to transmit a message by this alphabet, the following described
appliance is suggested: A matrix of cast iron, or made of any suitable
material, into which the person receiving the message (the pupil) places
his left hand, palm down, is fixed to the table or desk. The matrix,
fitting the hand, has twenty-six holes in it, corresponding in position
to the points upon the hand assigned to the different letters of the
alphabet. In these holes are small styles, or sharp points, which are so
placed as but slightly to touch the hand. Connected with each style is a
short line of wire, the other end of which is connected with a principal
wire leading to the desk of the operator (the teacher), and there so
arranged as to admit of opening and closing the circuit of an electric
current at will by the simple touch of a button, and thereby producing
along the line of that particular wire simultaneous electric impulses,
intended to act mechanically upon all the styles connected with it. By
these impulses, produced by the will of the sender, the styles are
driven upward with a quick motion, but with only sufficient force to be
felt and located upon the hand by the recipient. Twenty-six of these
principal or primary wires are run from the teacher's desk (there
connected with as many buttons) under the floor along the line of
pupils' desks. From each matrix upon the desk run twenty-six secondary
wires down to and severally connecting with the twenty-six primary wires
under the floor. The whole system of wires is incased so as to be out of
sight and possibility of contact with foreign substances. The keys or
buttons upon the desk of the teacher are systematically arranged,
somewhat after the order of those of the type writer, which allows the
use of either one or both hands of the operator, and of the greatest
attainable speed in manipulation. The buttons are labeled "a," "b," "c,"
etc., to "z," and an electric current over the primary wire running from
a certain button (say the one labeled "a") affects only those secondary
wires connected with the styles that, when excited, produce upon the
particular spot of the hands of the receivers the tactile impression to
be interpreted as "a." And so, whenever the sender touches any of the
buttons on his desk, immediately each member of the class feels upon the
palm of his hand the impression meant to be conveyed. The contrivance
will admit of being operated with as great rapidity as it is probable
human dexterity could achieve, i.e., as the strokes of an electric bell.
It was first thought of conveying the impressions directly by slight
electric shocks, without the intervention of further mechanical
apparatus, but owing to a doubt as to the physical effect that might be
produced upon the persons receiving, and as to whether the nerves might
not in time become partly paralyzed or so inured to the effect as to
require a stronger and stronger current, that idea was abandoned, and
the one described adopted. A diagram of the apparatus was submitted to a
skillful electrical engineer and machinist of Hartford, who gave as his
opinion that the scheme was entirely feasible, and that a simple and
comparatively inexpensive mechanism would produce the desired result.
[Illustration: TOUCH TRANSMISSION BY ELECTRICITY.]
The matter now to consider, and the one of greater interest to the
teacher of deaf children, is, Of what utility can the device be in the
instruction of deaf-mutes? What advantage is there, not found in the
prevailing methods of communication with the deaf, i.e., by gestures,
dactylology, speech and speech-reading, and writing?
I. The language of gestures, first systematized and applied to the
conveying of ideas to the deaf by the Abbe de l'Epee during the latter
part of the last century, has been, in America, so developed and
improved upon by Gallaudet, Peet, and their successors, as to leave but
little else to be desired for the purpose for which it was intended. The
rapidity and ease with which ideas can be expressed and understood by
this "language" will never cease to be interesting and wonderful, and
its value to the deaf can never fail of being appreciated by those
familiar with it. But the genius of the language of signs is such as to
be in itself of very little, if any, direct assistance in the
acquisition of syntactical language, owing to the diversity in the order
of construction existing between the English language and the language
of signs. Sundry attempts have been made to enforce upon the
sign-language conformity to the English order, but they have, in all
cases known to the writer, been attended with failure. The sign-language
is as immovable as the English order, and in this instance certainly
Mahomet and the mountain will never know what it is to be in each
other's embrace. School exercises in language composition are given with
great success upon the basis of the sign-language. But in all such
exercises there must be a translation from one language to the other.
The desideratum still exists of an increased percentage of pupils
leaving our schools for the deaf, possessing a facility of expression in
English vernacular. This want has been long felt, and endeavoring to
find a reason for the confessedly low percentage, the sign-language has
been too often unjustly accused. It is only when the sign-language is
abused that its merit as a means of instruction degenerates. The most
ardent admirers of a proper use of signs are free to admit that any
excessive use by the pupils, which takes away all opportunities to
express themselves in English, is detrimental to rapid progress in
English expression.
II. To the general public, dactylology or finger spelling is the
sign-language, or the basis of that language, but to the profession
there is no relation between the two methods of communication.
Dactylology has the advantage of putting language before the eye in
conformity with English syntax, and it has always held its place as one
of the elements of the American or eclectic method. This advantage,
however, is not of so great importance as to outweigh the disadvantages
when, as has honestly been attempted, it asserts its independence of
other methods. Very few persons indeed, even after long practice, become
sufficiently skillful in spelling on the fingers to approximate the
rapidity of speech. But were it possible for all to become rapid
spellers, another very important requisite is necessary before the
system could be a perfect one, that is, the ability to _read_ rapid
spelling. The number of persons capable of reading the fingers beyond a
moderate degree of rapidity is still less than the number able to spell
rapidly. While it is physically possible to follow rapid spelling for
twenty or thirty minutes, it can scarcely be followed longer than that.
So long as this is true, dactylology can hardly claim to be more than
one of the _elements_ of a system of instruction for the deaf.
III. Articulate speech is another of the elements of the eclectic
method, employed with success inversely commensurate with the degree of
deficiency arising from deafness. Where the English order is already
fixed in his mind, and he has at an early period of life habitually used
it, there is comparatively little difficulty in instructing the deaf
child by speech, especially if he have a quick eye and bright intellect.
But the number so favored is a small percentage of the great body of
deaf-mutes whom we are called upon to educate. When it is used as a
_sole_ means of educating the deaf as a class its inability to stand
alone is as painfully evident as that of any of the other component
parts of the system. It would seem even less practicable than a sole
reliance upon dactylology would be, for there can be no doubt as to what
a word is if spelled slowly enough, and if its meaning has been learned.
This cannot be said of speech. Between many words there is not, when
uttered, the slightest visible distinction. Between a greater number of
others the distinction is so slight as to cause an exceedingly nervous
hesitation before a guess can be given. Too great an imposition is put
upon the eye to expect it to follow unaided the extremely circumscribed
gestures of the organs of speech visible in ordinary speaking. The ear
is perfection as an interpreter of speech to the brain. It cannot
correctly be said that it is _more_ than perfection. It is known that
the ear, in the interpretation of vocal sounds, is capable of
distinguishing as many as thirty-five sounds per second (and oftentimes
more), and to follow a speaker speaking at the rate of more than two
hundred words per minute. If this be perfection, can we expect the _eye_
of ordinary mortal to reach it? Is there wonder that the task is a
discouraging one for the deaf child?
But it has been asserted that while a large percentage (practically all)
of the deaf _can_, by a great amount of painstaking and practice, become
speech readers in some small degree, a relative degree of facility in
articulation is not nearly so attainable. As to the accuracy of this
view, the writer cannot venture an opinion. Judging from the average
congenital deaf-mute who has had special instruction in speech, it can
safely be asserted that their speech is laborious, and far, very far,
from being accurate enough for practical use beyond a limited number of
common expressions. This being the case, it is not surprising that as an
unaided means of instruction it cannot be a success, for English neither
understood when spoken, nor spoken by the pupil, cannot but remain a
foreign language, requiring to pass through some other form of
translation before it becomes intelligible.
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