The permanence of character thus impressed upon speech exists only in
those regions to whose atmosphere our vocal organs are adapted. If
either the speaker or the hearer is placed in air differing greatly in
density from that to which they are accustomed, the voice of the one
will emit different sounds, or the same sounds will produce a different
impression on the ear of the other. But if both parties are placed in
this new atmosphere, their tones of communication will suffer the most
remarkable change. The two extreme positions, where such effects become
sufficiently striking, are in the compressed air of the diving-bell,
when it is immersed to a great depth in the sea, or in the rarefied
atmosphere which prevails on the summit of the Himalaya or the Andes.
In the region of common life, and even at the stillest hour of night,
the ear seldom rests from its toils. When the voice of man and the
bustle of his labours have ceased, the sounds of insect life are
redoubled; the night breeze awakens among the rustling leaves, and the
swell of the distant ocean, and the sounds of the falling cataract or
of the murmuring brook, fill the air with their pure and solemn music.
The sublimity of deep silence is not to be found even in the steppes
of the Volga, or in the forests of the Orinoco. It can be felt only in
those lofty regions
Where the tops of the Andes,
Shoot soaringly forth.
As the traveller rises above the limit of life and motion, and enters
the region of habitual solitude, the death-like silence which prevails
around him is rendered still more striking by the diminished density
of the air which he breathes. The voice of his fellow traveller ceases
to be heard even at a moderate distance, and sounds which would stun
the ear at a lower level make but a feeble impression. The report of
a pistol on the top of Mont Blanc is no louder than that of an Indian
cracker. But while the thinness of the air thus subdues the loudest
sounds, the voice itself undergoes a singular change: the muscular
energy by which we speak experiences a great diminution, and our powers
of utterance, as well as our power of hearing, are thus singularly
modified. Were the magician, therefore, who is desirous to impress upon
his victim or upon his pupil the conviction of his supernatural power,
to carry him, under the injunction of silence,
----------------------------- to breathe
The difficult air of the iced mountain’s top,
Where the birds dare not build, nor insect’s wing
Flit o’er the herbless granite,
he would experience little difficulty in asserting his power over
the elements, and still less in subsequently communicating the same
influence to his companion.
But though the air at the tops of our highest mountains is scarcely
capable of transmitting sounds of ordinary intensity, yet sounds of
extraordinary power force their way through its most attenuated strata.
At elevations where the air is three thousand times more rare than
that which we breathe, the explosion of meteors is heard like the
sound of cannon on the surface of the earth, and the whole air is often
violently agitated by the sound. This fact alone may give us some idea
of the tremendous nature of the forces which such explosions create,
and it is fortunate for our species that they are confined to the upper
regions of the atmosphere. If the same explosions were to take place in
the dense air which rests upon the earth, our habitations and our lives
would be exposed to the most imminent peril.
Buildings have often been thrown down by violent concussions of the
air, occasioned either by the sound of great guns or by loud thunder,
and the most serious effects upon human and animal life have been
produced by the same cause. Most persons have experienced the stunning
pain produced in the ear, when placed near a cannon that is discharged.
Deafness has frequently been the result of such sudden concussions,
and, if we may reason from analogy, death itself must often have
been the consequence. When peace was proclaimed in London, in 1697,
two troops of horse were dismounted and drawn up in line in order to
fire their volleys. Opposite the centre of the line was the door of a
butcher’s shop, where there was a large mastiff dog of great courage.
This dog was sleeping by the fire, but when the first volley was fired,
it immediately started up, ran into another room, and hid itself under
a bed. On the firing of the second volley, the dog rose, ran several
times about the room trembling violently, and apparently in great
agony. When the third volley was fired, the dog ran about once or twice
with great violence and instantly fell down dead, throwing up blood
from his mouth and nose.
Sounds of known character and intensity are often singularly changed
even at the surface of the earth, according to the state of the ground
and the conditions of the clouds. On the extended heath, where there
are no solid objects capable of reflecting or modifying sound, the
sportsman must frequently have noticed the unaccountable variety of
sounds which are produced by the report of his fowling-piece. Sometimes
they are flat and prolonged, at other times short and sharp, and
sometimes the noise is so strange that it is referred to some mistake
in the loading of the gun. These variations, however, arise entirely
from the state of the air, and from the nature and proximity of the
superjacent clouds. In pure air of uniform density the sound is sharp
and soon over, as the undulations of the air advance without any
interrupting obstacles. In a foggy atmosphere, or where the vapours
produced by heat are seen dancing as it were in the air, the sound is
dull and prolonged; and when these clouds are immediately over-head, a
succession of echoes from them produces a continued or reverberating
sound. When the French astronomers were determining the velocity of
sound by firing great guns, they observed that the report was always
single and sharp under a perfectly clear sky, but indistinct, and
attended by a long-continued roll like thunder, when a cloud covered
a considerable part of the horizon. It is no doubt owing to the same
cause, namely, the reflexion from the clouds, that the thunder rolls
through the heavens, as if it were produced by a succession of electric
explosions.
The great audibility of sounds during the night is a phenomenon of
considerable interest, and one which had been observed even by the
ancients. In crowded cities or in their vicinity, the effect was
generally ascribed to the rest of animated beings; while in localities
where such an explanation was inapplicable, it was supposed to arise
from a favourable direction of the prevailing wind. Baron Humboldt
was particularly struck with this phenomenon when he first heard the
rushing of the great cataracts of the Orinoco in the plain which
surrounds the Mission of the Apures. These sounds he regarded as
three times louder during the night than during the day. Some authors
ascribed this fact to the cessation of the humming of insects, the
singing of birds, and the action of the wind on the leaves of the
trees, but M. Humboldt justly maintains that this cannot be the cause
of it on the Orinoco, where the buzz of insects is much louder in the
night than in the day, and where the breeze never rises till after
sunset. Hence he was led to ascribe the phenomenon to the perfect
transparency and uniform density of the air, which can exist only at
night after the heat of the ground has been uniformly diffused through
the atmosphere. When the rays of the sun have been beating on the
ground during the day, currents of hot air of different temperatures,
and consequently of different densities, are constantly ascending from
the ground and mixing with the cold air above. The air thus ceases
to be a homogeneous medium, and every person must have observed the
effects of it upon objects seen through it which are very indistinctly
visible, and have a tremulous motion, as if they were “dancing in
the air.” The very same effect is perceived when we look at objects
through spirits and water that are not perfectly mixed, or when we view
distant objects over a red-hot poker or over a flame. In all these
cases the light suffers refraction in passing from a medium of one
density into a medium of a different density, and the refracted rays
are constantly changing their direction as the different currents rise
in succession. Analogous effects are produced when sound passes through
a mixed medium, whether it consists of two different mediums or of one
medium where portions of it have different densities. As sound moves
with different velocities through media of different densities, the
wave which produces the sound will be partly reflected in passing from
one medium to the other, and the direction of the transmission wave
changed: and hence in passing through such media different portions of
the wave will reach the ear at different times, and thus destroy the
sharpness and distinctness of the sound. This may be proved by many
striking facts. If we put a bell in a receiver containing a mixture of
hydrogen gas and atmospheric air, the sound of the bell can scarcely be
heard. During a shower of rain or of snow, noises are greatly deadened;
and when sound is transmitted along an iron wire or an iron pipe of
sufficient length, we actually hear two sounds, one transmitted more
rapidly through the solid, and the other more slowly through the air.
The same property is well illustrated by an elegant and easily repeated
experiment of Chladni’s. When sparkling champagne is poured into a tall
glass till it is half full, the glass loses its power of ringing by a
stroke upon its edge, and emits only a disagreeable and puffy sound.
This effect will continue while the wine is filled with bubbles of
air, or as long as the effervescence lasts; but when the effervescence
begins to subside the sound becomes clearer and clearer, and the glass
rings as usual when the air-bubbles have vanished. If we reproduce
the effervescence by stirring the champagne with a piece of bread, the
glass will again cease to ring. The same experiment will succeed with
other effervescing fluids.
The difference in the audibility of sounds that pass over homogeneous
and over mixed media is sometimes so remarkable as to astonish those
who witness it. The following fact is given on the evidence of an
officer who observed it:--When the British and the American forces
were encamped on each side of a river, the outposts were so near, that
the form of individuals could be easily distinguished. An American
drummer made his appearance, and began to beat his drum; but though
the motion of his arms was distinctly seen, not a single sound reached
the ear of the observer. A coating of snow that had newly fallen upon
the ground, and the thickness of the atmosphere, had conspired to
obstruct the sound. An effect the very reverse of this is produced by
a coating of glazed or hardened snow, or by an extended surface of ice
or water. Lieutenant Foster was able to carry on a conversation with
a sailor across Port Bowen Harbour, a distance of no less than a mile
and a quarter, and the sound of great guns has been heard at distances
varying from 120 to 200 miles. Over hard and dry ground of a uniform
character, or where a thin soil rests upon a continuous stratum of
rock, the sound is heard at a great distance, and hence it is the
practice among many Eastern tribes to ascertain the approach of an
enemy by applying the ear to the ground.
Many remarkable phenomena in the natural world are produced by the
reflexion and concentration of sound. Every person is familiar with
the ordinary _echo_ which arises from the reflexion of sound from an
even surface, such as the face of a wall, of a house, of a rock, of
a hill, or of a cloud. As sound moves at the rate of 1090 feet in a
second, and as the sound which returns to the person who emits it has
travelled over a space equal to twice his distance from the reflecting
surface, the distance in feet of the body which occasions the echo may
be readily found by multiplying 545 by the number of seconds which
elapse between the emission of the sound and its return in the form of
an echo. This kind of echo, where the same person is the speaker and
the hearer, never takes place, unless when the observer is immediately
in front of the reflecting surface, or when a line drawn from his mouth
to the flat surface is nearly perpendicular to it, because in this
case alone the wave of sound is reflected in the very same direction
from the wall in which it reaches it. If the speaker places himself
on one side of this line, then the echo will be heard most distinctly
by another person as far on the other side of it, because the waves
of sound are reflected like light, so that the angle of incidence or
the inclination at which the sound falls upon the reflected surface
is equal to the angle of reflexion, or the inclination at which the
sound is returned from the wall. If two persons, therefore, are placed
before the reflecting wall, the one will hear the echo of the sound
emitted by the other, and obstacles may intervene between these two
persons, so that neither of them hears the direct sound emitted by the
other; in the same manner as the same persons similarly placed before
a looking-glass would see each other distinctly by reflexion, though
objects might obstruct their direct view of each other.
Hitherto we have supposed that there is only one reflecting surface,
in which case there will be only one echo; but if there are several
reflecting surfaces, as in the case in an amphitheatre of mountains,
or during a thunder-storm, where there are several strata or masses
of clouds; or if there are two parallel or inclined surfaces between
which the sound can be repeatedly reflected, or if the surface is
curved, so that the sound reflected from one part falls upon another
part, like the sides of a polygon inscribed in a circle,--in all these
cases there will be numerous echoes, which produce a very singular
effect. Nothing can be more grand and sublime than the primary and
secondary echoes of a piece of ordnance discharged in an amphitheatre
of precipitous mountains. The direct or primary echoes from each
reflecting surface reach the ear in succession, according to their
different distances, and these are either blended with or succeeded
by the secondary echoes, which terminate in a prolonged growl, ending
in absolute silence. Of the same character are the reverberated claps
of a thunderbolt reflected from the surrounding clouds, and dying
away in the distance. The echo which is produced by parallel walls
is finely illustrated at the Marquis of Simonetta’s villa near Milan,
which has been described by Addison and Keysler, and which we believe
is that described by Mr. Southwell in the Philosophical Transactions
for 1746. Perpendicular to the main body of this villa there extend two
parallel wings about fifty-eight paces distant from each other, and the
surfaces of which are unbroken either with doors or windows. The sound
of the human voice, or rather a word quickly pronounced, is repeated
above forty times, and the report of a pistol from fifty-six to sixty
times. The repetitions, however, follow in such rapid succession that
it is difficult to reckon them, unless early in the morning before the
equal temperature of the atmosphere is disturbed, or in a calm, still
evening. The echoes appear to be best heard from a window in the main
building between the two projecting walls, from which the pistol also
is fired. Dr. Plot mentions an echo in Woodstock Park which repeats
seventeen syllables by day and twenty by night. An echo on the north
side of Shipley church, in Sussex, repeats twenty-one syllables. Sir
John Herschel mentions an echo in the Manfroni palace at Venice, where
a person standing in the centre of a square room about twenty-five
feet high, with a concave roof, hears the stamp of his foot repeated
a great many times; but as his position deviates from the centre, the
echoes become feebler, and at a short distance entirely cease. The
same phenomenon, he remarks, occurs in the large room of the library
of the museum at Naples. M. Genefay has described, as existing near
Rouen, a curious oblique echo which is not heard by the person who
emits the sound. A person who sings hears only his own voice, while
those who listen hear only the echo, which sometimes seems to approach,
and at other times seems to recede from the ear; one person hears a
single sound, another several sounds, and one hears it on the right,
and another on the left, the effect always changing as the hearer
changes his position. Dr. Birch has described an extraordinary echo at
Roseneath, in Argyleshire, which certainly does not now exist. When
eight or ten notes were played upon a trumpet, they were correctly
repeated, but on a key a third lower. After a short pause, another
repetition of the notes was heard in a still lower tone, and after
another short interval they were repeated in a still lower tone.
In the same manner as light is always lost by reflexion, so the
waves of sound are enfeebled by reflexion from ordinary surfaces,
and the echo is in such cases fainter than the original sound. If
the reflecting surface, however, is circular, sound may be condensed
and rendered stronger in the same manner as light. I have seen a
fine example of this, in the circular turn of a garden wall nearly
a mile distant from a weir across a river. When the air is pure and
homogeneous, the rushing sound of the water is reflected from the
hollow surface of the wall, and concentrated in a focus, the place of
which the ear can easily discover from the intensity of the sound being
there a maximum. A person not acquainted with the locality conceives
that the rushing noise is on the other side of the wall.
In whispering galleries, or places where the lowest whispers are
carried to distances at which the direct sound is inaudible, the sound
may be conveyed in two ways, either by repeated reflexions from a
curved surface in the direction of the sides of a polygon inscribed
in a circle, or where the whisperer is in the focus of one reflecting
surface, and the hearer in the focus of another reflecting surface,
which is placed so as to receive the reflected sounds. The first of
these ways is exemplified in the whispering gallery of St. Paul’s,
and in the octagonal gallery of Gloucester cathedral, which conveys
a whisper seventy-five feet across the nave; and the second in the
baptistery of a church in Pisa, where the architect, Giovanni Pisano,
is said to have constructed the cupola on purpose. The cupola has an
elliptical form, and when one person whispers in one focus, it is
distinctly heard by the person placed in the other focus, but not by
those who are placed between them. The sound first reflected passes
across the cupola, and enters the ears of the intermediate persons,
but it is too feeble to be heard till it has been condensed by a
second reflexion to the other focus of ellipse. A naval officer,
who travelled through Sicily in the year 1824, gives an account of
a powerful whispering place in the cathedral of Girgenti, where the
slightest whisper is carried with perfect distinctness through a
distance of two hundred and fifty feet, from the great western door to
the cornice behind the high altar. By an unfortunate coincidence, the
focus of one of the reflecting surfaces was chosen for the place of the
confessional; and when this was accidentally discovered, the lovers
of secrets resorted to the other focus, and thus became acquainted
with confessions of the gravest import. This divulgence of scandal
continued for a considerable time, till the eager curiosity of one
of the dilettanti was punished, by hearing his wife’s avowal of her
own infidelity. This circumstance gave publicity to the whispering
peculiarity of the cathedral, and the confessional was removed to a
place of greater secrecy.
[Illustration: _Fig. 51._]
An echo of a very peculiar character has been described by Sir John
Herschell in his Treatise on Sound, as produced by the suspension
bridge across the Menai strait in Wales. “The sound of a blow with a
hammer,” says he, “on one of the main piers, is returned in succession
from each of the cross-beams which support the road-way, and from the
opposite pier at a distance of five hundred and seventy-six feet; and
in addition to this, the sound is many times repeated between the
water and the road-way. The effect is a series of sounds which may be
thus written: the first return is sharp and strong from the road-way
over-head; the rattling which succeeds dies away rapidly, but the
single repercussion from the opposite pier is very strong, and is
succeeded by a faint palpitation, repeating the sound at the rate of
twenty-eight times in five seconds, and which, therefore corresponds to
a distance of a hundred and eighty-four feet, or very nearly the double
interval from the road-way to the water. Thus it appears that in the
repercussion between the water and road-way, that from the latter only
affects the ear, the line drawn from the auditor to the water being
too oblique for the sound to diverge sufficiently in that direction.
Another peculiarity deserves especial notice, namely, that the echo
from the opposite pier is best heard when the auditor stands precisely
opposite to the middle of the breadth of the pier, and strikes just
on that point. As it deviates to one or the other side, the return is
proportionally fainter, and is scarcely heard by him when his station
is a little beyond the extreme edge of the pier, though another person,
stationed (on the same side of the water) at an equal distance from the
central point, so as to have the pier between them, hears it well.”
A remarkable subterranean echo is often heard when the hoofs of a horse
or the wheels of a carriage pass over particular spots of ground. This
sound is frequently very similar to that which is produced in passing
over an arch or vault, and is commonly attributed to the existence of
natural or artificial caves beneath. As such caves have often been
constructed in times of war as places of security for persons and
property, many unavailing attempts have been made to discover hidden
treasures where their locality seemed to be indicated by subterraneous
sounds. But though these sounds are sometimes produced by excavations
in the ground, yet they generally arise from the nature of the
materials of which the ground is composed, and from their manner of
combination. If the hollow of a road has been filled up with broken
rock, or with large waterworn stones, having hollows either left
entirely empty, or filled up with materials of different density, then
the sound will be reflected in passing from the loose to the dense
materials, and there will arise a great number of echoes reaching the
ear in rapid succession, and forming by their union a hollow rumbling
sound. This principle has been very successfully applied by Sir John
Herschell to explain the subterranean sounds with which every traveller
is familiar who has visited the Solfaterra, near Naples. When the
ground at a particular place is struck violently by throwing a large
stone against it, a peculiar hollow sound is distinctly heard. This
sound has been ascribed by some geologists to the existence of a great
vault communicating with the ancient seat of the volcano, by other
writers to a reverberation from the surrounding hills with which it
is nearly concentric, and by others to the porosity of the ground.
Dr. Daubeny, who says that the hollow sound is heard when any part
of the Solfaterra is struck, accounts for it by supposing that the
hill is not made up of one entire rock, but of a number of detached
blocks, which, hanging as it were by each other, form a sort of vault
over the abyss within which the volcanic operations are going on.[24]
Mr. Forbes, who has given the latest and most interesting description
of this singular volcano,[25] agrees in opinion with Dr. Daubeny;
while Mr. Scrope[26] and Sir John Herschell concur in opinion that
no such cavities exist. “It seems most probable,” says the latter,
“that the hollow reverberation is nothing more than an assemblage
of partial echoes arising from the reflexion of successive portions
of the original sound, in its progress through the soil at the
innumerable half-coherent surfaces composing it: were the whole soil
a mass of sand, these reflexions would be so strong and frequent as
to destroy the whole impulse in too short an interval to allow of a
distinguishable after-sound. It is a case analogous to that of a strong
light thrown into a milky medium or smoky atmosphere; the whole medium
appears to shine with a nebulous undefined light. This is to the eye
what such a hollow sound is to the ear.”[27]
[24] Description of Volcanoes, p. 170.
[25] _Edinburgh Journal of Science_, New Series, No. i., p. 124.
[26] Considerations on Volcanoes, and _Edinburgh Journal of Science_,
No. xx., p. 261, and No. xiv., p. 265.
[27] Art. SOUND, _Encycl. Metrop._, § 110.
It has been recently shown by M. Savart, that the human ear is so
extremely sensible as to be capable of appreciating sounds which
arise from about _twenty-four thousand_ vibrations in a second, and
consequently that it can hear a sound which lasts only the twenty-four
thousandth part of a second. Vibrations of such frequency afford only
a shrill squeak or chirp; and Dr. Wollaston has shown that there are
many individuals with their sense of hearing entire, who are altogether
insensible to such acute sounds, though others are painfully affected
by them. Nothing, as Sir John Herschell remarks, can be more surprising
than to see two persons, neither of them deaf, the one complaining of
the penetrating shrillness of a sound, while the other maintains there
is no sound at all. Dr. Wollaston has also shown that this is true also
of very grave sounds; so that the hearing or not hearing of musical
notes at both extremities of the scale seems to depend wholly on the
pitch or frequency of vibration constituting the note, and not upon the
intensity or loudness of the noise. This affection of the ear sometimes
appears in cases of common deafness, where a shrill tone of voice, such
as that of women and children, is often better heard than the loud and
deeper tone of men.
Dr. Wollaston remarked, that when the mouth and nose are shut, the
tympanum or drum of the ear may be so exhausted by a forcible attempt
to take breath by the expansion of the chest, the pressure of the
external air upon the membrane gives it such a tension, that the ear
becomes insensible to grave tones, without losing in any degree the
perception of sharper sounds. Dr. Wollaston found, that after he had
got into the habit of making the experiment, so as to be able to
produce a great degree of exhaustion, his ears were insensible to
all sounds below F, marked by the bass clef. “If I strike the table
before me,” says he, “with the end of my finger, the whole board sounds
with a deep dull note. If I strike it with my nail, there is also at
the same time a sharp sound produced by quicker vibrations of parts
around the point of contact. When the ear is exhausted, it hears only
the latter sound, without perceiving in any degree the deeper note of
the whole table. In the same manner, in listening to the sound of a
carriage, the deeper rumbling noise of the body is no longer heard by
an exhausted ear; but the rattle of a chain or loose screw remains at
least as audible as before exhaustion.” Dr. Wollaston supposes that
this excessive tension of the drum of the ear, when produced by the
compressed air in the diving-bell, will also produce a corresponding
_deafness to low tones_. This curious experiment has been since made
by Dr. Colladon, when descending in the diving-bell at Howth, in 1820.
“We descended,” says he, “so slowly that we did not notice the motion
of the bell; but as soon as the bell was immersed in water, we felt
about the ears and the forehead a sense of pressure, which continued
increasing during some minutes. I did not, however, experience any pain
in the ears; but my companion suffered so much that we were obliged
to stop our descent for a short time. To remedy that inconvenience,
the workmen instructed us, after having closed our nostrils and mouth,
to endeavour to swallow, and to restrain our respiration for some
moments, in order that, by this exertion, the internal air might act
on the Eustachian tube. My companion, however, having tried it, found
himself very little relieved by this remedy. After some minutes, we
resumed our descent. My friend suffered considerably; he was pale; his
lips were totally discoloured; his appearance was that of a man on the
point of fainting; he was in involuntary low spirits, owing, perhaps,
to the violence of the pain, added to that kind of apprehension which
our situation unavoidably inspired. This appeared to me the more
remarkable, as my case was totally the reverse. I was in a state of
excitement resembling the effect of some spirituous liquor. I suffered
no pain; I experienced only a strong pressure round my head, as if an
iron circle had been bound about it. I spoke with the workmen, and had
some difficulty in hearing them. This difficulty of hearing rose to
such a height, that during three or four minutes I could not hear them
speak. I could not, indeed, hear myself speak, though I spoke as loudly
as possible; nor did even the great noise caused by the violence of the
current against the sides of the bell reach my ears.”
The effect thus described by Dr. Colladon is different from that
anticipated by Dr. Wollaston. He was not merely deaf to low tones, but
to all sounds whatever; and I have found, by repeated experiment, that
my own ears become perfectly insensible even to the shrill tones of the
female voice, and of the voice of a child, when the drum of the ear is
thrown into a state of tension by yawning.
With regard to sounds of high pitch at the other extremity of the
scale, Dr. Wollaston has met with persons, whose hearing was in
other respects perfect, who never heard the chirping of the _Gryllus
campestris_, which commonly occurs in hedges during a summer’s evening,
or that of the house-cricket, or the squeak of the bat, or the chirping
of the common house-sparrow. The note of the bat is a full octave
higher than that of the sparrow; and Dr. Wollaston believes that the
note of some insects may reach one octave more, as there are sounds
decidedly higher than that of a small pipe, one-fourth of an inch in
length, which he conceives cannot be far from six octaves above the
middle E of the pianoforte. “The suddenness of the transition,” says
Dr. Wollaston, “from perfect hearing to total want of perception,
occasions a degree of surprise, which renders an experiment on this
subject with a series of small pipes among several persons rather
amusing. It is curious to observe the change of feeling manifested
by various individuals of the party, in succession, as the sounds
approach and pass the limits of their hearing. Those who enjoy a
temporary triumph are often compelled in their turn to acknowledge to
how short a distance their little superiority extends.” In concluding
his interesting paper on this subject, Dr. Wollaston conjectures that
animals, like the grylli (whose powers of hearing appear to commence
nearly where ours terminate), may have the power of hearing still
sharper sounds which at present we do not know to exist, and that there
may be other insects having nothing in common with us, but who are
endowed with a power of exciting, and a sense of perceiving, vibrations
which make no impression upon our organs, while their organs are
equally insensible to the slower vibrations to which we are accustomed.
With the view of studying the class of sounds inaudible to certain
ears, we would recommend it to the young naturalist to examine the
sounds emitted by the insect tribe, both in relation to their effect
upon the human ear, and to the mechanism by which they are produced.
The Cicadæ or locusts in North America appear, from the observations
of Dr. Hildreth,[28] to be furnished with a bagpipe on which they play
a variety of notes. “When any one passes,” says he, “they make a great
noise and screaming with their air bladder or bagpipes. These bags are
placed under, and rather behind, the wings in the axilla, something in
the manner of using the bagpipes with the bags under the arms--I could
compare them to nothing else; and, indeed, I suspect the first inventor
of the instrument borrowed his ideas from some insect of this kind.
They play a variety of notes and sounds, one of which nearly imitates
the scream of the tree toad.”
[28] _Edinburgh Journal of Science_, No. xvii., p. 158.
Among the acoustic wonders of the natural world may be ranked the
vocal powers of the statue of Memnon, the son of Aurora, which modern
discoveries have withdrawn from among the fables of ancient Egypt.
The history of this remarkable statue is involved in much obscurity.
Although Strabo affirms that it was overturned by an earthquake, yet as
Egypt exhibits no traces of such a convulsion, it has been generally
believed that the statue was mutilated by Cambyses. Ph. Casselius,
in his dissertation on vocal or speaking stones, quotes the remark
of the scholiast in Juvenal, “that, when mutilated by Cambyses, the
statue, which saluted both the sun and the king, afterwards saluted
only the sun.” Philostratus, in his life of Apollo, informs us, that
the statue looked to the east, and that it spoke as soon as the rays
of the rising sun fell upon its mouth. Pausanias, who saw the statue
in its dismantled state, says, that it is a statue of the sun, that
the Egyptians call it Phamenophis, and not Memnon, and _that it emits
sounds every morning at sunrise, which can be compared only to that of
the breaking of the string of the lyre_. Strabo speaks only of a single
sound which he heard; but Juvenal, who had probably heard it often
during his stay in Egypt, describes it as if it emitted several sounds:
Dimidio magicæ resonant ubi Memnone chordæ.
Where broken Memnon sounds his magic strings.
The simple sounds which issued from the statue were, in the progress
of time, magnified into intelligible words, and even into an oracle of
seven verses, and this prodigy has been recorded in a Greek inscription
on the left leg of the statue. But though this new faculty of the
colossus was evidently the contrivance of the Egyptian priests, yet we
are not entitled from this to call in question the simple and perfectly
credible fact that it emitted sounds. This property, indeed, it seems
to possess at the present day; for we learn,[29] that an English
traveller, Sir A. Smith, accompanied with a numerous escort, examined
the statue, and that at six o’clock in the morning he heard very
distinctly the sounds which had been so celebrated in antiquity. He
asserts that this sound does not proceed from the statue, but from the
pedestal; and he expresses his belief that it arises from the impulse
of the air upon the stones of the pedestal, which are arranged so as
to produce this surprising effect. This singular description is, to a
certain extent, confirmed by the description of Strabo, who says, that
he was quite certain that he heard a sound which proceeded either _from
the base_, or from the colossus, or from some one of the assistants. As
there were no Egyptian priests in the escort of Sir A. Smith, we may
now safely reject this last, and, for many centuries, the most probable
hypothesis.
[29] _Revue Encyclopédique_, 1821, tome ix., p. 592.
The explanation suggested by Sir A. Smith had been previously given in
a more specific form by M. Dussaulx, the translator of Juvenal. “The
statue,” says he, “being hollow, the heat of the sun heated the air
which it contained, and this air, issuing at some crevice, produced the
sounds of which the priests gave their own interpretation.”
Rejecting this explanation, M. Langles, in his dissertation on the
vocal statue of Memnon, and M. Salverte, in his work on the occult
sciences, have ascribed the sounds entirely to Egyptian priestcraft;
and have even gone so far as to describe the mechanism by which
the statue not only emitted sounds, but articulated distinctly the
intonations appropriate to the seven Egyptian vowels, and consecrated
to the seven planets. M. Langles conceives that the sounds may be
produced by a series of hammers, which strike either the granite
itself, or sonorous stones like those which have been long used in
China for musical instruments. M. Salverte improves this imperfect
apparatus, by supposing that there might be adapted to these hammers a
clepsydra, or water-clock, or any other instrument fitted to measure
time, and so constructed as to put the hammers in motion at sunrise.
Not satisfied with this supposition, he conjectures that the spring of
all this mechanism was to be found in the art of concentrating the rays
of the sun, which was well known to the ancients. Between the lips of
the statue, or in some less remarkable part of it concealed from view
by its height, he conceives an aperture to be perforated, containing a
lens or a mirror capable of condensing the rays of the rising sun upon
one or more metallic levers, which by their expansion put in motion
the seven hammers in succession. Hence he explains why the sounds were
emitted only at sunrise, and when the solar rays fell upon the mouth of
the statue, and why they were never again heard till the sun returned
to the eastern horizon. As a piece of mechanism, this contrivance is
defective in not providing for the change in the sun’s amplitude,
which is very considerable even in Egypt, for as the statue and the
lens are both fixed, and as the sounds were heard at all seasons of
the year, the same lens which threw the Midsummer rays of the sun upon
the hammers could not possibly throw upon them his rays in winter. But
even if the machinery were perfect, it is obvious that it could not
have survived the mutilation of the statue, and could not, short of a
miracle, have performed its part in the time of Sir A. Smith.
If we abandon the idea of the whole being a trick of the priesthood,
which has been generally done, and which the recent observations of
Sir A. Smith authorise us to do, we must seek some natural cause for
the phenomena similar to that suggested by Dussaulx. It is curious
to observe how the study of nature gradually dispels the consecrated
delusions of ages, and reduces to the level of ordinary facts what time
had invested with all the characters of the supernatural: and in the
present case it is no less remarkable that the problem of the statue of
Memnon should have been first solved by means of an observation made
by a solitary traveller wandering on the banks of the Orinoco. “The
granitic rock,” says Baron Humboldt, “on which we lay, is one of those
where travellers on the Orinoco have heard from time to time, towards
sunrise, subterraneous sounds resembling those of the organ. The
missionaries call these stones _loxas de musica_. ‘It is witchcraft,’
said our young Indian pilot. We never ourselves heard these mysterious
sounds either at Carichana Vieja or in the upper Orinoco: but from
information given us by witnesses worthy of belief, the existence of a
phenomenon that seems to depend on a certain state of the atmosphere
cannot be denied. The shelves of rock are full of very narrow and
deep crevices. They are heated during the day to about 50°. I often
found their temperature at the surface during the night at 39°, the
surrounding atmosphere being at 28°. It may easily be conceived that
the difference of temperature between the subterraneous and the
external air attains its maximum about sunrise, or at that moment which
is at the same time farther from the period of the maximum of the heat
of the preceding day. May not these sounds of an organ, then, which are
heard when a person sleeps upon the rock, his ear in contact with the
stone, be the effect of a current of air that issues out through the
crevices? Does not the impulse of the air against the elastic spangles
of mica that intercept the crevices contribute to modify the sounds?
May we not admit that the ancient inhabitants of Egypt, in passing
incessantly up and down the Nile, had made the same observation on some
rock of the Thebaid, and that the music of the rocks there led to the
jugglery of the priests in the statue of Memnon?”
This curious case of the production of sounds in granite rocks at
sunrise might have been regarded as a transatlantic wonder which was
not applicable to Egypt; but by a singular coincidence of observation,
Messrs. Jomard, Jollois, and Devilliers, who were travelling in Egypt
nearly about the same time that M. Humboldt was traversing the wilds of
South America, heard, _at sunrise, in a monument of granite_, situated
near the centre of the spot on which the palace of Carnac stands, _a
noise resembling that of a breaking string_, the very expression by
which Pausanias characterizes the sound in the Memnonian granite. The
travellers regarded these sounds as arising from the transmission
of rarefied air through the crevices of a sonorous stone, and they
were of the same opinion with Humboldt, that these sounds might have
_suggested_ to the Egyptian priests _the juggleries of the Memnonium_.
Is it not strange that the Prussian and the French travellers should
not have gone a step farther, and solved the problem of two thousand
years, by maintaining that the sound of the statue of Memnon was itself
a natural phenomenon, or a granitic sound elicited at sunrise by the
very same causes which operated on the Orinoco and in the temple of
Carnac, in place of regarding it as a trick in imitation of natural
sounds? If, as Humboldt supposes, the ancient inhabitants of Egypt
had, in passing incessantly up and down the Nile, become familiar with
the music of the granite rocks of the Thebaid, how could the imitation
of such natural and familiar sounds be regarded by the priests as a
means of deceiving the people? There could be nothing marvellous in
a colossal statue of granite giving out the very same sounds that
were given out at the same time of the day by a granite rock; and in
place of reckoning it a supernatural fact, they could regard it in no
other light than as the duplicate of a well-known natural phenomenon.
It is a mere conjecture, however, that such sounds were common in the
Thebaid; and it is therefore probable that a granite rock, possessing
the property of emitting sounds at sunrise, had been discovered by the
priests, who were at the same time the philosophers of Egypt, and that
the block had been employed in the formation of the Memnonian statue
for the purpose of impressing upon it a supernatural character, and
enabling them to maintain their influence over a credulous people.
The inquiries of recent travellers have enabled us to corroborate
these views, and to add another remarkable example of the influence of
subterraneous sounds over superstitious minds. About three leagues to
the north of Tor in Arabia Petræa, is a mountain, within the bosom of
which the most singular sounds have been heard. The Arabs of the Desert
ascribe these sounds to a convent of monks preserved miraculously
underground; and the sound is supposed to be that of the _Nakous_, a
long narrow metallic ruler suspended horizontally, which the priest
strikes with a hammer for the purpose of assembling the monks to
prayer. A Greek was said to have seen the mountain open, and to have
descended into the subterranean convent, where he found fine gardens
and delicious water; and, in order to give proof of his descent, he
produced some fragments of consecrated bread, which he pretended to
have brought from the subterranean convent. The inhabitants of Tor
likewise declare that the camels are not only frightened, but rendered
furious, when they hear these subterraneous sounds.
M. Seetzen, the first European traveller who visited this extraordinary
mountain, set out from Wodyel Nackel on the 17th of June, at five
o’clock in the morning. He was accompanied by a Greek Christian and
some Bedouin Arabs, and after a quarter of an hour’s walk they reached
the foot of a majestic rock of hard sand-stone. The mountain itself was
quite bare and entirely composed of it. He found inscribed upon the
rock several Greek and Arab names, and also some Koptic characters,
which proved that it had been resorted to for centuries. About noon the
party reached the foot of the mountains called _Nakous_, where at the
foot of a ridge they beheld an insulated peaked rock. This mountain
presented upon two of its sides two sandy declivities about 150 feet
high, and so inclined that the white and slightly adhering sand which
rests upon its surface is scarcely able to support itself; and when the
scorching heat of the sun destroys its feeble cohesion, or when it is
agitated by the smallest motions, it slides down the two declivities.
These declivities unite behind the insulated rock, forming an acute
angle, and like the adjacent surfaces, they are covered with steep
rocks which consist chiefly of a white and friable free-stone.
The first sound which greeted the ears of the travellers took place
at an hour and a quarter after noon. They had climbed with great
difficulty as far as the sandy declivity, a height of seventy or
eighty feet, and had rested beneath the rocks where the pilgrims are
accustomed to listen to the sounds.
While in the act of climbing, M. Seetzen heard the sound from beneath
his knees, and hence he was led to think that the sliding of the sand
was the cause of the sound, and not the effect of the vibration which
it occasioned. At three o’clock the sound became louder and continued
six minutes, and after having ceased for ten minutes, it was again
heard. The sound appeared to have the greatest resemblance to that
of the humming-top, rising and falling like that of an Æolian harp.
Believing that he had discovered the true origin of the sound, M.
Seetzen was anxious to repeat the experiment, and with this view he
climbed with the utmost difficulty to the highest rocks, and sliding
down as fast as he could, he endeavoured, with the help of his hands
and feet, to set the sand in motion. The effect thus produced far
exceeded his expectations, and the sand in rolling beneath him made so
loud a noise, that the earth seemed to tremble to such a degree that he
states he should certainly have been afraid if he had been ignorant of
the cause.
M. Seetzen throws out some conjectures respecting the cause of
these sounds. Does the rolling layer of sand, says he, act like the
fiddle-bow, which, on being rubbed upon a plate of glass, raises
and distributes into regular figures the sand with which the plate
is covered? Does the adherent and fixed layer of sand perform here
the part of the plate of glass, and the neighbouring rocks that of
the sounding body? We cannot pretend to answer these questions,
but we trust that some philosopher competent to the task will have
an opportunity of examining these interesting phenomena with more
attention, and describing them with greater accuracy.
The only person, so far as I can learn, who has visited El-Nakous,
since the time of Seetzen, is Mr. Gray, of University College,
Oxford; but he has not added much to the information acquired by his
predecessor. During the first visit which he made to the place, he
heard at the end of a quarter of an hour a low continuous murmuring
sound beneath his feet, which gradually changed into pulsations as
it became louder, so as to resemble the striking of a clock, and at
the end of five minutes it became so strong as to detach the sand.
Returning to the spot next day, he heard the sound still louder than
before. He could not observe any crevices by which the external air
could penetrate; and as the sky was serene and the air calm, he was
satisfied that the sounds could not arise from this cause.[30]
[30] See _Edinburgh Journal of Science_, No. xi., p. 153, and No.
xiii., p. 51.