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produced by a telephone in the same circuit. In all such cases the
effect is increased by the use of "an induction-coil ; and the sensitive
cells can be employed for the reproduction of articulate speech, as well
as for the production of musical sounds.

We have also found that loud sounds are produced from lamp-
black by passing through it an intermittent electrical current ; and
that it can be used as a telephonic receiver for the reproduction of
articulate speech by electrical means.

A convenient mode of arranging a lampblack cell for experimental

purposes is shown in Fig. 9. When
an intermittent current is passed
through the lampblack (A), or when
an intermittent beam of sunlight
falls upon it through the glass plate
(B), a loud musical tone can be
heard by applying the ear to the
hearing-tube (C). When the light
and the electrical current act simul-
taneously, two musical tones arr
perceived, which produce beats when nearly of tli.

same pitch. By proper arrangements a completi

interference of sound can undoubtedly be produced.

Upox the Measuremext of the SOXOROI >

I ] Effects produced by Different Substaxcp:s, —

yWe have observed that different substances produce
sounds of very different intensities under similar cir-
cumstances of experiment, and it has appeared to us
that very valuable information might be obtained if
we could measure the audible effects produced. For this purpose we
have constructed several different forms of apparatus for studying
the effects, but, as our researches are not yet complete, I shall confine
myself to a simple description of some of the forms of apparatus w*
have devised.

"When a beam of light is brought to a focus by means of a lens,
the beam diverging from the focal point becomes weaker as the dis-
tance increases in a calculable degree. Hence, if we can determine
the distances from the focal point at which two different substances
emit sounds of equal intensity, we can calculate their relative sonorous
powers.

Preliminary experiments were made by Mr. Tainter, during my
absence in Europe, to ascertain the distance from the focal point of a
lens at which the sound produced by a substance became inaudible.
A few of the results obtained will show the enormous differences ex-
isting between different substances in this respect.



PRODUCTION OF SO VXD BY BAD TAX T EXERGY. 327

DISTANCE FHO.M FOCAL POINT OF LENS AT WHICn SOUNDS BECOME INAUDIBLE
WITH DIFFEUENT SUBSTANCES.

:SIetn-s.

Zinc diaphragm (polished) 1 •">!

Hard-rubber diaphragm 1 DU

Tin-foil *' 2-00

Telephone " (japanned iron) 2'15

Zinc • (unpolished) 215

White silk, (in receiver shown in Fig. 1.) 3 10

White worsted, " " " 4-01

Yellow worsted, " " " 4*06

Yellow silk, " " " 4-13

White cotton-wool, " " " 4'38

Green silk, " " " 4-52

Blue worsted, " " " 4-69

Purple silk, " - " 4-82

Brown silk, ■ " 5-02

Black silk, - " 5-21

Red silk, " " " 5-24

Black worsted, " " " 6-50

Lampblack. In receiver the limit of audibility could not be determined, on

account of want of space. Sound perfectly audible at a distance of. .10-00

Mr. Tainter was convinced from these experiments that this field
of research promised valuable results, and he at once devised an ap-
paratus for studying the effects, which he described to me upon my
return from P^urope. The apparatus has since been constructed, and
I take great pleasure in showing it to you to-day.

1. A beam of light is received by two similar lenses (A B, Fig.
10), which bring the light to a focus on either side of the interrupting
disk (C). The tvs^o substances, whose sonorous powers are to be com-
pared, are placed in the receiving vessels (D E) (so arranged as to ex-
pose equal surfaces to the action of the beam) which communicate, by
flexible tubes (F G) of equal length, with the common hearing-tube
(II). The receivers (D E) are placed upon slides, which can be moved
along the graduated supports (I K), Tlie beams of light passing
through the interrupting disk (C) are alternately cut off by the swing-
ing of a pendulum (L). Thus a musical tone is produced alternately
from the substance in D and from that in E. One of the receivers is
kept at a constant point upon its scale, and the other receiver is moved
toward or from the focus of its beam until the ear decides that the
sounds produced from D and E are of equal intensity. The relative
positions of the receivers are then noted.

2. Another method of investigation is based upon the production
of an interference of sound, and the apparatus employed is shown in
Fig. 11. The interrupter consists of a tuning-fork (A, Fig. 11, a),
which is kept in continuous vibration bv means of an electro-mag-
net (B).

A powerful beam of light is brought to a focus between the prongs



THE POPULAR SCIENCE MONTHLY.



of the tuning-fork (A), and the passage of the beam is more or less
obstructed by the vibration of the opaque screens (C D) carried by
the prongs of the fork.

As the tuning-fork (A) produces a sound
by its own vibration, it is placed at a suffi-
cient distance away to be inaudible through
the air, and a system of lenses is employed
for the purpose of bringing the undulating
beam of light to the receiving lens (E)
with as little loss as possible. The two
receivers (F G) are attached to slides (H I)
which move upon opposite sides of the
axis of the beam, and the receivers are
connected by flexible tubes of unequal
length (K L) communicating with the
common hearing-tube (M).

The length of the tube (K) is such
that the sonorous vibrations from the re-
ceivers (F G) reach the common hearing-
tube (M) in opposite phases. Under these
circumstances silence is produced Avhen
the vibrations in the receivers (F G) are
of equal intensity. When the intensities
are unequal, a residual effect is perceived.
In operating the instrument the position
of the receiver (G) remains constant, and
the receiver (F) is moved to or from the
focus of the beam until complete silence
is produced. The relative positions of the
two receivers are then noted, -

3. Another
mode is as fol-
lows : The loud-
ness of a musi-
cal tone pro-
duced by the action of liglit is compared
with the loudness of a tone of similar
pitch produced by electrical means. A
rheostat introduced into the circuit en-
ables us to measure the amount of re-
sistance required to render the electrical
sound equal in intensity to the other.

4, If the tuning-fork (A) in Fig, 11 is '- \J

thrown into vibration by an undulatory

instead of an intermittent current passed through the electro-magnet
(B), it is probable that a musical tone, electrically produced in the re-




PRODUCTION OF SOUND BY RADIANT ENERGY. 329



Fig. 11, a.




ceiver (F) by the action of the same current, wouUI be found capable
of extinguishing the effect produced in the receiver (G) by the action
of the undulatory beam of light, in which case it should be possible to
establish an acoustic balance be-
tween the effects produced by
light and electricity by introduc-
ing sufficient resistance into the
electric circuit.

Upon the Xature of the
Rays that troduce Sonorous
Effects in Different Sub-
stances. — In my paper read be-
fore the American Association
last August, and in the present
paper, I have used the word
" light " in its usual rather than
its scientific sense, and I have not
hitherto attempted to discrimi-
nate the effects produced by the
different constituents of ordinary
light — the thermal, luminous, and
actinic rays. I find, however, that
the adoption of the word "pho-
tophone " by Mr. Tainter and my-
self has led to the assumption
that we believed the audible ef-
fects discovered by us to be due
entirely to the action of luminous
rays. The meaning we have uni-
formly attached to the words
" photophone " and " light " will
be obvious from the following
passage, quoted from my Boston
paper :

Althoupli effects are produced, as
above shown, by forms of radiant en-
ergy, which are invisible, we liavo
named the apparatus for the produc-
tion and reproduction of sound in tliis
way the " photophone," became an
ordinary beam of light contains the
"ii/s ichich are operatite.

To avoid in future any misun-
derstandings upon this point, we
have decided to adopt the terin
• radiophone,'''' proposed by ]M.



U^.




33°



THE POPULAR SCIENCE MONTHLY





Mercadier, as a general term signifying an apparatus for the production
of sound by any form of radiant energy, limiting the words thermo-
phone, photophone, and actinophone to apparatus for the production
of sound by thermal, luminous, or actinic rays respectively.

M. Mercadier, in the course of his researches
in radiophony, passed an intermittent beam
from an electric lamp through a prism, and
then examined the audible effects produced in
different parts of the spectrum ("Coraptes
Rendus," December 6, 1880).

We have repeated this experiment, using
the sun as our source of radiation, and have ob-
tained results somewhat different from those
noted by M. Mercadier.

A beam of sunlight Avas reflected from a
heliostat (A, Fig. 12) through an achromatic
lens (B), so as to form an image of the sun
upon the slit (C).

The beam then passed through another ach-
romatic lens (D), and through a bisulphide-of-
carbon prism (E), forming a spectrum of great
intensity, which, when focused upon a screen,
was found to be sufticiently pure to show the
principal absorption lines of the solar spec-
trum.

The disk-interrupter (F) was then turned
with suflicient rapidity to produce from five
to six hundred interruptions of the light per
second, and the spectrum was explored with
the receiver (G), which was so arranged that
the lampblack surface exposed was limited by
a slit, as shown.

Under these circumstances sounds were ob-
tained in every part of the visible spectrum,
excepting the extreme half of the violet, as
well as in the u.ltra-red. A continuous increase
in the loudness of the sound was observed upon
moving the receiver (G) gradually from the
violet into the ultra-red. The point of maxi-
mum sound lay very far out in the ultra-red.
Beyond this point the sound began to de-
crease, and then stopped so suddenly that a
very slight motion of the receiver (G) made
all the difference between almost maximum
sound and complete silence.
2. The lampblacked wire gauze was then removed, and the in-



PRODUCTION OF SOUND BY RADIANT ENERGY. 331

terior of the receiver (G) was filled with red worsted. Upon explor-
ing the spectrum as before, entirely different results were obtained.
The maximum effect was produced in the green at that part where
the red worsted appeared to be black. On either side of this point
the sound gradually died away, becoming inaudible on the one side in
the middle of the indigo, and on the other at a short distance outside
the edge of the red.

3. Upon substituting green silk for red worsted, the limits of audi-
tion appeared to be the middle of the blue and a point a short distance
out in the ultra-red — maximum in the red.

■i. Some hard-rubber shavings were now i)laced in the receiver
(G). The limits of audibility appeared to be, on the one hand, the
junction of the green and blue, and, on the other, the outside edge of
the red — maximum in the yellow. Mr. Tainter thought he could
hear a little way into the ultra-red, and to his ear the maximum was
about the junction of the red and orange.

o. A test-tube containing the vapor of sulphuric ether was then
substituted for the receiver (G). Commencing at the violet end, the
test-tube was gradually moved down the spectrum and out into the
ultra-red without audible effect, but, when a certain point far out in
the ultra-red was reached, a distinct musical tone suddenly made its
appearance, which disappeared as suddenly on moving the test-tube a
very little farther on.

6. Upon exploring the spectrum with a test-tube containing the
vapor of iodine, the limits of audibility appeared to be the middle of
the red and the junction of the blue and indigo — maximum in the
green.

7. A test-tube containing peroxide of nitrogen was substituted for
that containing iodine. Distinct sounds were obtained in all parts of
the visible spectrum, but no sounds were observed in the ultra-red.

The maximum effect seemed to mo to be in the blue. The sounds
were well marked in all parts of the violet, and I even fancied that
the audible effect extended a little way into the ultra-violet, but of
this I can not be certain. Upon examining the absorption spectrum
of peroxide of nitrogen it was at once observed that the maximum
sound was produced in that part of the spectrum where the greatest
number of absorption lines made their appearance.

8. The spectrum was now explored by a selenium cell, and the
audible effects were observed by means of a telephone in the same
galvanic circuit with the cell. The maximum effect was produced in
the red. The audible effect extended a little way into the ultra-red on
the one hand and up as high as the middle of the vuolet on the other.

Although the experiments so far made can only be considered as
preliminary to others of a more refined nature, I think we are war-
ranted in concluding that the nature of the rays that j^'oduce sonorous
'jfects in dijferent substances depends upon the nature of the substances



33'



THE POPULAR SCIEXCE MONTHLY.



that are exposed to tJie beam, and that the sounds are in every case due
to those rays of the spectrum that are absorbed by the body.

The Spectrophoxe. — Our experi-
ments upon the range of audibility of
different substances in the spectrum
have led us to the construction of a
new instrument for use in spectrum
analysis, Avhich was described and ex-
hibited to the Philosophical Society of
Washington last Saturday.* The eye-
piece of a spectroscope is removed, and
sensitive substances are placed in the
focal point of the instrument behind
an opaque diaphragm containing a slit.
These substances are put in ■ communi-
cation with the ear by means of a hear-
ing-tube, and thus the instrument is con-
verted into a verita-
ble " spectrophone,"
like that shown in
Fig. 13.

Suppose we smoke
the interior of our
spectrophonic receiv-
er, and fill the cavity
with peroxide of ni-
trogen gas. We have
then a combination
that gives iis good
sounds in all parts of
the spectrum (visible
and invisible), ex-
cept the ultra-violet.
Now, pass a rapidly-
interrupted beam of
light through some
substance whose ab-
sor])tion spectrum is
to be investigated,
and bands of sound
and silence are ob-
served upon exploring the spectrum, the silent positions correspond-
ing to the absorption bands. Of course, the ear can not for one mo-
ment compete with the eye in the examination of the visible part
of the spectrum ; but in the invisible part beyond the red, where
"Proceedings of the Philosophical Society" of Washington, April IG, ISSI.




PRODUCTION OF SOUND BY RADIANT ENERGY. 333



the oye is useless, the ear is
invaluable. In working in
this region of the spectrum,
lampblack alone may be used
in the spectrophonic receiver.
Indeed, the sounds produced
by this substance in the ultra-
red are so well marked as to
constitute our instrument a
most reliable and convenient
substitute for the thermopile.
A few experiments that have
been made may be interest-
ing.

1. The interrupted beam
was filtered through a sat-
urated solution of alum.

Result : The range of au-
dibility in the ultra-red was
slightly reduced by the ab-
sorption of a narrow band of
the rays of lowest refran-
gibility. The sounds in the
visible part of the spectrum
seemed to be unaffected.

2. A thin sheet of hard
rubber was interposed in the
path of the beam.

Result : Well-marked
sounds in every part of the
ultra-red. No sounds in the
visible part of the spectrum,
excepting the extreme half
of the red.

These experiments reveal
the cause of the curious fact
alluded to in my paper read
before the American Asso-
ciation last August — that
sounds were heard from se-
lenium when the beam was
filtered through both hard
rubber and alum at the same
time. (See table of results in
Fig. U.)
A solution of ammonia-sulphate of copper was tried.






334 THE POPULAR SCIEXCE MOXTHLY.

Result : When placed in the path of the beam, the spectrum disap-
peared, with the exception of the blue and violet end. To the eye the
spectrum was thus reduced to a single broad band of blue-violet light.
To the ear, however, the spectrum revealed itself as two bands of
sound, with ^ broad sjiace of silence between. The invisible rays
transmitted constituted a narrow band just outside the red.

I think I have said enough to convince you of the value of this new
method of examination, but I do not wish you to understand that wo
look upon our results as by any means complete. It is often niort
interesting to observe the first totterings of a child than to watch the
firm tread of a full-grown man, and I feel that our first footsteps in
this new field of science may have more of interest to you than the
fuller results of mature research. This must be my excuse for having
dwelt so long upon the details of incomplete experiments.

I recognize the fact that the spectrophone must ever remain a mere
adjunct to the spectroscope, but I anticipate that it has a wide and in-
dependent field of usefulness in the investigation of absorption spectra
in the ultra-red.



PHYSICAL E D U C A T I O X .

Br FELIX L. OSWALD, M. D.

SLEEP.

"Cliildren, stinted in their sleep, are never wide-awake." — Pestalozzi.

THE vital, processes of man, like those of all his fellow-creatures,
are partly controlled by automatic tendencies. Some function >
of our internal economy are too important to be trusted to the caprices
of human volition ; breathing, eating, drinking, and even love, are
only semi-voluntary actions ; and during a period varying from one
fourth to two fifths of each solar day the conscious activity of the
senses undergoes a complete suspense : the cerebral workshop is closed
for repairs, and the abused or exhausted body commits its organism
into the healing hands of Nature. Under favorable conditions eight
hours of undisturbed sleep would almost suffice to counteract the
physiological mischief of the sixteen waking hours. During slee})
the organ of consciousness is at rest, and the energies of the system
seem to be concentrated on the function of nutrition and the renewal
of the vital energy in general ; sleep promotes digestion, repairs the
waste of the muscular tissue, favors the process of cutaneous excretion,
and renews the vigor of the mental faculties.

The amount of sleep required by man is generally proportionate
to the waste of vital strength, whether by muscular exertion, mental



PH VSICA L ED UCA TIOX.



335



activity (or emotion), or by the process of rapid assimilation, as during
the tirst years of growth and during the recovery from an exhaust-
ing disease. The weight of a new-born child increases more rapidly
than that of a eupeptic adult, enjoying a liberal diet after a period of
starvation, and, though an infant is incapable of forming aljstract ideas,
we need not doubt that the variety of new and bewildering impres-
sions must overtask its little sensorium in a few hours. Nurslings
should therefore be permitted to sleep to their full satisfaction ; weakly
babies, especially, need sleep more than food, and it is the safest plan
never to disturb a child's slumber while the regularity of his breathing
indicates the healthfulness of his repose ; there is little danger of his
" oversleeping " himself in a moderately warmed, well-ventilated room.
Never mind about meal-times : hunger will awaken him at the right
moment, or teach him to make up for lost time. Three or four nurs-
ings in the twenty-four hours are enough ; Dr. C. E. Page, who has
made the problem of infant diet his special study, believes that fifty
per cent, of the enormous number of children dying under two years
of age are killed by being coaxed to guzzle till they are hopelessly
diseased with fatty degeneration.*

The healthfulness of village-children is partly due to the tranquil-
lity of their slumber in the comfortable nooks of a quiet homestead,
or in the shade of a leafy tree, while their parents are at work in a way
rather incompatible with the habit of fondling the baby all night. In
houses whei-e there is plenty of room, the nursery and the infant's
dormitory ought to be two separate apartments : the play-room can
not be too sunny ; for the bedroom a shady and sequestered location
is, on the whole, preferable. Next to out-door exercise, silence and a
subdued light are the best hypnotics. But under no circumstances
should insomnia be overcome by cradling or narcotics. Stupefaction
is not slumber. The lethargy induced by rocking and cradling is akin
to the drowsy torpor of a sea-sick passenger, and the opium-doctor
might as well benumb his patient by a whack on the head. The
morbid sleeplessness of children may be owing to several causes which
can be generally recognized by the symptoms of their modus operandi ;
impatient turning from side to side, as if in a vain attempt to obtain
a much-needed repose, means that the room is too stuffy or too warm ;
long wakefulness, combined with squalling-fits and petulant move-
ments, indicates acidity in the stomach (overfeeding, or too much
"soothing-sirup") — let the little kicker exercise his muscle on the
floor ; in malignant cases, skip a meal or two, or give water instead of

* '' The only wonder is that any infant lives sixty days from birth. Fed before birth
but three times a day he is after birth subjected to ten or twenty meals in the twenty-
four hours, until chronic dyspepsia or some acute disease interferes. ... So far from
admitting a possible error in advising three meals only, I am convinced that, for a hand-
fed baby especially, two would often be better than three."— (" IIow to feed a Baby to
make it healthy and happy," p. 55.)



336 THE POPULAR SCIEXCE MOXTHLY.

milk. After weathering an attack of croup, children often lie motion-
less on their backs with a peculiar glassy stare of their wide-open eyes.
Leave them alone ; instinct teaches them to assuage the distress of
their lungs by slow and deep respirations ; rest and a half-open win-
dow will do them more good than medicine.

Healthful infants — i. e., under rational management the great plu-
rality — can soon be taught to transact their public business at season-
able hours, or at least to abstain from midnight serenades. If mothers
would make it a rule to do all their nursing and fondling in the daytime,
their little revivalists would soon learn to associate darkness with the
idea of silence and slumber. Habit will do wonders in such things.
Captain Barclay and several American pedestrians learned to take
their half-hour naps as a traveler snatches a hasty lunch, and many
old soldiers develop a faculty of going off to sleep, as it were, at the
word of command, the moment their shoulders touch the guard-
house bunk. The two drowsiest years of my life I passed at an old-
style boarding-school, where teachers and pupils were limited to seven
hours of sleep, after nine hours of stud}-, besides written exercises and
special recitations, and Avhere sixty or seventy of us had to sleep in
a large hall ; and I do not believe that the last flickering of our five-
minutes candle was ever witnessed by a pair of more than half-open
eyes.

But that same faculty of sleeping and waking at short notice may
be utilized for the purpose of taking little naps whenever opportunity
offers — in the last half-hour of the noontide recess, or during the
Buncombe interacts of a protracted session. The inhabitants of all
intertropical countries make the time of repose a movable festival, and
during the dog-days of our torrid summers it would clearly be the best
plan to imitate their example. " Children must not sleep in the day-
time," says a by-law of our time-dishonored Koran of domestic super-
stitions ; and, not satisfied with keeping our little ones at school during
the drowsy afternoons of the summer solstice, we increase their misery
by stuffing them at the very noon of the hottest hours Avith a mass of
greasy (1. e., heat-producing and soporific) food. An hour after the
end of a long, sultry day comes the cool night-wind, heaven's own
blessing for all who hunger and thirst after fresh air ; but no, " Night-
air is injurious " ; besides, Mrs. Grundy objects to promenades after



Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 41 of 110)