_Origin of the Crescent as the Turkish Ensign.--Apparitions
dispelled by Philosophy.--Musical instruments classed under
three divisions.--Mixed instruments.--Theory of wind
instruments.--The Jew’s Harp.--The Statue of Memnon.--An
interesting experiment.--The Flute.--The whiz-gig,
etc.--Echoes.--The Whispering Gallery in the Dome of St.
Paul’s.--The Speaking Trumpet.--The Invisible Girl.--Other
Acoustic Amusements._
On entering the library on the following morning, Mr. Seymour informed
Miss Villers, that Major Snapwell had taken his departure, in order to
breakfast with the vicar, and that he had invited Tom and Louisa to
accompany him, for the sake of inspecting the cabinet of medals; but he
added, that he expected the return of the party at two o’clock, when he
proposed to give them a lecture upon the philosophy of the several toys
which are indebted for their action to atmospheric vibrations.
“Suppose, then,” said Miss Villers, “that we walk towards Forest Lane,
and meet them on their return. This arrangement,” she added, “will
afford me an opportunity of communicating to you the history of some
adventures I encountered last evening, and of taking your opinion upon
them.”
“You well know,” answered Mr. Seymour, “that you may always command my
services--but you have really raised my curiosity: what can be the
nature of the adventures you speak of?”
Miss Villers then entered into a particular account of all she saw and
heard the preceding evening; with which the reader is already
acquainted. Mr. Seymour, however, suggested the propriety of abstaining
from any discussion upon the subject until the children were present to
hear it; for, said he, “I am most desirous that they should be
familiarized with those natural sources of illusion which enlighten the
wise, while they minister to the superstitious fears of the ignorant.”
They had not reached the entrance of Forest Lane, before they perceived
the vicar with Tom and Louisa, followed by the Major.
“Papa,” cried Tom, as he ran to meet his father, “we have had a most
delightful morning; amongst other things, do you know we have found out
the meaning of the crescent which the Turks always wear, and use as
their ensign.”
“Indeed! well, then, let me hear your explanation,” said his father.
Major Snapwell and the vicar had by this time joined the party, and
with their assistance Tom was enabled to offer the following account of
it.--The crescent appears on the early coins of Byzantium, and was
intended to commemorate the defeat of Philip of Macedon, who, as he was
about to storm it on a cloudy night, was discovered by the sudden light
of the moon. When the Turks entered Constantinople, they found this
ancient badge in various parts of the city, and suspecting that it
might possess some magical power, they assumed the symbol and its power
to themselves; so that the crescent became, and still continues to be,
the chief Turkish ensign.
“Well, I must own that you have given me a new and very curious piece
of historical information, and I thank you for it,” said Mr. Seymour.
“Medals, then, are occasionally of some little use,” remarked the
vicar, with a sarcastic smile; for if the truth must be told, the
reverend antiquary had been a little nettled as usual by the freedom
with which Major Snapwell had criticised some of his rarities; but let
that pass.
As soon as the party reassembled after the excursion of the morning,
the circumstances which so greatly astonished Miss Villers on the
preceding evening, were again related by her.
“My dear young lady,” observed Mr. Seymour, “I never heard a better
story for illustrating the illusions to which the senses are exposed;
and if you will read the second letter on ‘Natural Magic,’ by Sir David
Brewster, you will obtain a ready explanation of your vision--but let
us examine it philosophically. In the first place you acknowledge that
your imagination had been previously excited during your ramble through
the wood, and more especially by your reverie at the statue of Time;
now it is well known that such a condition of the mind prepares and
adapts the organs of vision for those illusions which I am about to
explain. You have told us that, on your descent into the valley, the
moon had withdrawn its light, and several minutes had elapsed before an
object became visible, and that was the _white_ foam of the waterfall.”
“If I rightly remember, Brewster has stated that the spectres that are
conjured up by the imagination are always _white_, because no other
colour can be seen at night,” observed Mrs. Seymour.
“Undoubtedly,” replied her husband; “and as these spectres are formed
out of objects whose different parts reflect different degrees of
light, their fainter parts will appear and disappear with the ever
varying degree of illumination which is occasioned by the moon shining
through a veil of clouds, and a change even of shape will be thus
produced which will impart to the object in question the semblance of a
living form. The actual state of the eye itself will also greatly
assist in completing such an illusion; for, in consequence of the small
degree of light, the pupil expands to nearly the whole width of the
iris, in order to collect every ray, and in such a condition it cannot
accommodate itself to see near objects distinctly, so that the form of
a body actually becomes more shadowy and confused when it comes within
the very distance at which we count upon obtaining the best view of it.”
“You have certainly explained the reason why bodies seen under a faint
illumination may appear distorted and caricatured; indeed, I now
remember that Sir Walter Scott, in his “Pirate,” has given us a very
good illustration; for Cleveland when abandoned on Coffin bay is said
to have seen many a dim and undefined spectre in the misty dawn. But I
am still at a loss to understand how the vision I witnessed in the
valley could have been conjured up,” said Miss Villers.
“It was the doubtful and flickering light of the clouded moon upon the
mass of white sandstone,” said Mr. Seymour. “It is a great law of the
imagination, that a likeness in part tends to become a likeness of the
whole. The sandstone presented, in the first instance, a form somewhat
resembling the human figure, or some part of it, when your active
imagination immediately completed the outline; just in the same way as
we trace images in the fire, or castles in the clouds, or grotesque
figures of men and animals on damp walls.”(46)
“I am satisfied,” said Miss Villers, “and I thank you, and Sir David
Brewster, for the lecture; and now,” continued the lady, “how will you
explain the circumstance of my name having been so audibly pronounced,
and from a spot which made it impossible that it should have come from
any human being?”
“It was the solitary spirit of the dell,” said Mr. Seymour, with a
smile; “a rural spirit who is disposed to become very loquacious
whenever the repose of her habitation is disturbed. I can assure you,”
added he, “that you are not the first person whom her gambols have
surprised and terrified in the shades of evening. I presume you have
discovered that I allude to that unseen musician of the air--ECHO.”
“Indeed, Mr. Seymour, the sound could not have been the effect of an
echo, for I never spoke,” replied Miss Villers.
“Very likely, but I happen to know that Mrs. Seymour called you by name
at the orchard gate.”
“Nor will that explain it,” observed Miss Villers, “for in that case I
must certainly have heard her, whereas the sound came in a very
different direction, from the inaccessible rocks of sandstone.”
“Young lady,” said Mr. Seymour, “you must forgive me for telling you
that your philosophy is at fault. It is as possible to hear an echo,
without recognising the direct sound which produced it, as it is for
two persons to be so placed as to see each other in a looking-glass,
although objects might obstruct the direct view of themselves. Did you
never walk between an irregular wall and a row of houses, or along a
valley intercepted by houses during the ringing of a peal of bells?
Nothing is more common under such circumstances, for the sound instead
of arriving at the ear, in its true direction, to be reflected in one
that is opposite to it;--now before we quit the subject of optical
illusion, let me relate an incident which occurred to myself. I presume
you are all acquainted with the appearance in the grass, called a
_Fairy-ring_?”
“To be sure,” said Tom, “a very dark circle of grass, around which
there is generally a ring that looks as if the ground had been burnt.”
“Very well,--and we are now satisfied that this appearance is the
consequence of the growth and decay of certain fungi(47), although the
common people still believe that the ring is produced by the gambols of
fairies--now then for my story. It was on a moonlight night, last
August, when strolling along a neighbouring meadow, enjoying the
beauties of the evening, that I met a young farmer, an intelligent
person, although a little inclined to a belief in the marvellous, who,
on approaching with a hasty step, thus accosted me;--‘You have often
ridiculed my belief in fairies, and of their being the cause of those
rings which go by their name; you may now, if you please, satisfy
yourself of their reality, if you will only return with me to the elm
close, which, as you know, abounds with fairy-rings. Within the last
few minutes I have actually seen them at their gambols under the great
elm; they are, sir, tiny beings which, as far as I could judge at a
distance, cannot be more than a few inches in height; but there they
are, frisking away most merrily: pray, sir, do let us return, and
satisfy yourself as well as me.’--You may readily suppose that I lost
no time in complying with my friend’s request; and sure enough there
they were.”
“What, the fairies!” exclaimed Louisa, in astonishment.
“Have patience, my dear, and you shall hear. I confess,” continued Mr.
Seymour, “that at the first glance, I was almost startled into a belief
in the reality of my friend’s assertion, but on approaching, the Fairy
Queen and her court were changed into a circle of fungi, to which the
shadowy play of the leaves of the neighbouring tree had, in the light
of the moon, given the appearance of a fantastic motion. The illusion,
I will admit, was very extraordinary, and one well calculated to impose
upon the credulous countrymen.”
The young party were much amused by the anecdote, and the vicar took
this opportunity to explain, on natural principles, several
superstitious appearances recorded in ancient legends.
Mr. Seymour now proposed to dedicate an hour to the explanation of the
several toys which owe their action to atmospheric vibration; “I shall
then,” said he, addressing Miss Villers, “be at your service to
interrogate the spirit of the valley; and the children, whom I intend
to accompany us, will be thus better prepared to comprehend the theory
of the echo.”
“Musical instruments, amongst which I include the toys to which I have
alluded, may be classed under three heads:--_stringed_ instruments,
such as the harp, violin, &c.; _wind_ instruments, as the flute and
trumpet; and instruments of _percussion_, as the tabor and drum.”
“And which kind do you consider the most ancient?” asked Miss Villers.
“_Wind_ instruments, madam, most unquestionably,” cried Mr. Twaddleton.
“Diodorus ascribed their invention to the accidental notice of the
whistling of the wind in the reeds, on the banks of the Nile; and the
poet Lucretius maintained a similar opinion.”
“I really, my dear Sir, cannot see any good reason for giving this
preference, in point of antiquity, to wind instruments,” said Mr.
Seymour. “The lyre, or harp, is, surely, as ancient as any instrument
on record. The mythologist ascribes the idea of producing sound by the
vibration of a string, to Apollo; which is said by Censorinus to have
suggested itself to him, on his hearing the twang of the bow of his
sister Diana. With respect to instruments of percussion, it may be
reasonably supposed that the sonorous ringing of hollow bodies, when
struck, must have very soon suggested their invention to mankind; but I
really consider any research into a question of such obscurity as
uninteresting as it must be hopeless; let us rather devote our
attention to the philosophy of these instruments. I have stated that
they may be referred to three principal classes; but I must at the same
time observe that, in some cases, the vibrations of solid bodies are
made to co-operate with those of a given portion of air; for example,
trumpets and various horns may be said to be mixed wind instruments,
since their sound is produced by the joint vibrations of the air and a
solid body; and in certain stringed instruments, as in the violin, the
immediate effect of the strings is increased by means of a
sounding-board, which appears to be agitated by their motion, and to
act more powerfully on the air than the strings could have done alone.”
“I apprehend that this mixture must obtain more or less in all
instruments,” said the vicar.
“Not at all. The flute, flageolet, humming-top, and the cavity of the
mouth in whistling, may be considered as simple wind instruments, in
which the quality of the sound is alone determined by the vibrations of
the air. I have already explained the manner in which the oscillations
of a string excite aërial undulations, and thus produce sound; and you
have seen that the nature of these sounds is determined by the length
and thickness of such strings: the theory equally applies to wind
instruments, in which case, a column of air corresponds with the
string, the volume and length of which determines the sound. In the
harp, the strings are constructed of different lengths and dimensions;
and so, in the _Syrinx_, or _Pan’s pipes_, is the volume of air
adjusted to the respective notes by the size and length of the reeds;
but, in the violin, the lengths of the strings are altered at pleasure
by pressing them down on the finger-board; and, in like manner, the
effective length of the flute is changed by the opening or shutting the
holes made at proper distances in them; the opening of a hole at any
part being the same in effect as if the pipe were cut off a little
beyond it.”
Mr. Seymour and the vicar then entered into a long discussion, with
which it is not our intention to swell our history, or to exhaust the
patience of the reader; we shall, however, with his permission, collect
from the mass some of the more interesting facts, and present them in
as condensed a form as may be consistent with perspicuity. In speaking
of the _Jew’s harp_, a little instrument with which every school-boy is
well acquainted, the vicar stated that its origin was lost in the long
lapse of time; but that it was in very common use throughout Europe,
and more especially in the Netherlands and the Tyrol, where it was the
delight of the peasants and their families. He also said that it was
known in Asia, and that the Greeks of Smyrna called it, in imitation of
its sound, _biambo_. The name by which it is now known, he observed,
was evidently derived from the Jews, who were formerly the great
venders of it, and of other toys throughout Europe, although he stated
that his friend Mr. Prybabel was of opinion that it was a corruption of
_jaw’s_ harp. Mr. Seymour described its construction, and the theory of
its action. [Illustration: Jew’s harp.] It is composed of two parts,
the _body_ and the _tongue_: the former has some resemblance to the
handle of a certain kind of corkscrew; the latter consists of a little
strip of steel, joined to the upper part of the body, and bent at its
extremity, so that the fingers may touch it more readily. This tongue,
or elastic plate, produces, in itself, only a sound which serves as a
drone, although it appears to act like the motion of the bow of a
violin in exciting other sounds, by breaking the current of air from
the mouth, the acuteness or gravity of which will be determined by the
pressure of the lips, and the magnitude of the cavity of the mouth. To
understand, however, this part of its operation, it is necessary that
the reader should become acquainted with the nature and effects of what
have been termed _Resonances, and Reciprocated Vibrations of Columns of
Air_. This property of sounding bodies, which to the ignorant must
appear as an inexplicable species of sympathy, will be more fully
explained in a note(48); at present we shall merely give one or two
examples of its effects. A singer has been known to break into pieces a
large tumbler glass by the power of his voice; and a violin suspended
against a wall may be heard to yield the same notes as those produced
by a performer on a similar instrument in the same room. To produce
such an effect, however, one condition is indispensable, that the body
to be put in vibration must be in unison, or agreeing in pitch, with
the one communicating the sound. Hence the necessity of so adapting the
capacity of the mouth in playing the Jew’s harp, as to make the column
of air which it contains to reciprocate the sound of its tongue. The
subject was agreeably concluded by some anecdotes which were related by
Miss Villers, in proof of the astonishing powers of this little
instrument when directed by the skill of a master. For the sake of
those who may be curious upon this subject we have introduced an
account of two great performers, in an additional note(49). In speaking
of the flute, Mr. Twaddleton took occasion to observe, that its name
was derived from _fluta_,[57] a lamprey, or small Sicilian eel, which
has seven holes on each side; an etymology which will probably be as
new to our readers as it was to ourselves. The children also received
their share of instruction and amusement upon this occasion. Tom, for
the first time, became acquainted with the use of the pea in the
whistle, which, he was told, was to agitate and break the current of
air, and thus to produce a succession of quick vibrations upon which
the acuteness of its sound depended. Louisa exhibited her _whiz-gig_,
which, for the information of the unlearned reader, we may state to
consist of a hollow disc of wood, having an opening in its side, like
that in the humming-top; by the alternate coiling and uncoiling of the
cord upon which it is strung it receives a circular motion, the
rapidity of which produces, by means of its opening, an aërial
vibration that gives a loud ringing sound.
“I should very much like to hear your opinion of that Egyptian wonder,
the statue of Memnon,” said the vicar.
“Its history,” answered Mr. Seymour, “is involved in considerable doubt
and difficulty. Authors of credit agree in stating that it certainly
saluted the rising sun with a musical sound; but doubts are still
entertained as to the cause which produced it, whether it was the
effect of mechanism, or a juggle of the Egyptian priests. An English
traveller, Sir A. Smith, informs us that he visited the statue, and
actually heard the sounds at six o’clock in the morning; but he
believes that they proceeded, not from the figure, but from the
pedestal, and he considers that they may arise from the impulse of the
air upon the stones of which it is constructed. Others have supposed
that the heat of the sun’s rays, concentrated by a mirror, may have
acted upon plates of metal so as to produce the effect. It is not my
intention to argue this point; but I will show you an experiment, by
which you will, I think, be convinced that a statue might easily be
constructed like the Memnon to yield musical sounds by the application
of heat, whether derived from the solar rays, or from any other source.”
[Illustration: The “piece of apparatus” described below.]
Mr. Seymour produced a piece of apparatus, of which we here present the
reader with a sketch. It consists of an oblong block of copper, one
surface of which is flat, the other formed by two planes meeting at an
obtuse angle, and having a groove at the point of junction A. To this
block a handle is affixed.
Mr. Seymour having thus described the form of the instrument, and
stated that its construction was solely directed with a view of making
it oscillate freely on any plain surface, thrust the block in the fire,
and when sufficiently heated, placed it on its angular surface, upon a
flat piece of lead. It immediately began to vibrate, producing at
first, a kind of singing noise, not unlike that of the simmering of a
teakettle, but the vibrations became more and more rapid until a
distinct musical sound was produced, which from time to time varied in
its pitch, and gave rise to an effect scarcely inferior to that of the
Eolian harp.
“How extremely beautiful!” said Miss Villers.
“And how admirably does it illustrate the theory of musical sounds,”
observed Mr. Seymour. “We have here, you perceive, a series of impulses
communicated to our ears by the air, at first in slow succession, and
by degrees more and more rapidly; at first we hear a rattling noise,
then a low murmur, and then a hum, which by degrees acquires the
character of a musical note, rising higher and higher in acuteness. It
is evident, therefore, from this experiment alone, by showing the
correspondence which exists between the pitch of the note and the
rapidity of the succession of the vibrations, that our sensation of the
different pitches of musical notes originates in the different
rapidities with which their impulses are communicated to our ears.”
“Pray explain to us the manner in which the block of metal is thus made
to vibrate,” said Miss Villers.
“It depends,” replied Mr. Seymour, “upon the alternate contraction of
the two opposite edges of the metal from the loss of heat; one of the
edges coming in contact with the cold lead contracts, and by destroying
the balance of the block, causes its opposite edge to come into contact
with the lead, and to undergo the same change; and it is by this
alternate action that a rapid vibration is produced, occasioning, as
you will now readily understand, the musical sounds you have just
heard.”
The lecture having been concluded, Mrs. Seymour proposed that the party
should, at once, proceed to the valley, but the vicar suggested the
propriety of first explaining to the children the principle upon which
the echo depended.
Mr. Seymour concurred in this opinion, and immediately afforded the
following explanation:--“An echo is nothing more than a reflected
sound. When the aërial vibrations strike against any obstacle of
sufficient magnitude, they are reflected back to the ear, and produce a
repetition of the sound, which will appear to proceed from the point
whence they are reflected, so that the apparent direction of the voice
becomes completely changed by an echo. A considerable extent of level
wall will sometimes produce it in great perfection; for a smooth
surface reflects sounds much better than a rough one: but the
circumstance which, perhaps, contributes more than any other to the
perfection of an echo, is the form of the reflecting surface; a convex
surface is a very bad reflector of sound, a flat one reflects very
well, but a small degree of concavity is the form best adapted to the
purpose.”
“I believe,” observed the vicar, “that fluid bodies will also, under
certain circumstances, so reflect sound as to produce echoes.”
“Undoubtedly. The surface of water, especially at the bottom of a well;
and sometimes even clouds will produce this effect.”
“Do you mean to say, papa,” asked Tom, “that sound is reflected from an
obstacle to the ear, in the same manner as my ball is reflected after
striking the wall?”
“Certainly: supposing, of course, that your ball is perfectly elastic;
and in that case, you no doubt remember the direction it will follow.”
“It will always make the angle of _reflection_ equal to the angle of
_incidence_,”[58] said Tom.
“Undoubtedly; and so it is with sound, since air, as you know, is
perfectly elastic. If, therefore, the vibrations fall perpendicularly
on the obstacle, they are reflected back in the same line; if
obliquely, the sound returns obliquely in the opposite direction, the
angle of reflection being equal to that of incidence. You will,
therefore, readily perceive,” continued Mr. Seymour, addressing his
conversation more particularly to Miss Villers, “that a person situated
at an appropriate angle may hear an echo, as it is returned from the
reflecting surface, without hearing the original sound which produced
it. 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.”
“As a smooth and concave surface is capable of producing an echo, how
does it happen that we so rarely meet with one in a room?” asked Louisa.
“Echoes, my dear, are, in fact, produced in every room, by the
reverberation of sound from its walls; but on account of the velocity
with which it travels, they are imperceptible in small chambers,
because the sound occupies no sensible period of time in moving from
the mouth to the walls, and in returning back to the ear again,
consequently the original sound and its echo become so blended and
incorporated, as to appear but one sound. As the dimensions of the
apartment increase, the defect will increase with it; and, in buildings
for music or public speaking, it is often highly inconvenient, and
difficult of prevention. Breaking the surface, or rendering it uneven
by mouldings and ornaments, appears to be the most effectual method of
curing the evil.”
“I perceive then, papa, that in order to produce a perfect echo, the
person who speaks must be at a considerable distance from the obstacle
that reflects the sound,” said Louisa.
“It cannot be otherwise,” replied her father; “and if you will only
consider the rate at which sound travels, you will readily understand
the necessity of such an arrangement. In order to produce a distinct
echo of one syllable, or of a single sound, the reflecting obstacle
must be at least 70 feet from the sound, so that it may have to pass
through a distance of 70 feet to get to the reflector, and 70 more to
return to the ear, making a total passage of 140 feet, which it will
accomplish in rather less than one-eighth of a second; a period of time
so small, that, if it were diminished, it is evident the echo must be
assimilated with the sound itself.”
“But the echo in the valley,” observed Mrs. Seymour, “will repeat four
or five syllables.”
“Undoubtedly. If we make the experiment at a sufficient distance from
the sandstone rocks which act as the reflector.”
“It would appear, then, that the farther the reflecting object is off,
the greater number of syllables will the echo repeat; and I should
think that this fact might enable us to compute the distance of the
reflector,” said Mrs. Seymour.
“In a moderate way of speaking, about three and a half syllables are
pronounced in one second, or seven syllables in two seconds; when an
echo, therefore, repeats seven syllables, we may infer that the
reflecting object is 1142 feet distant.”
“But, my dear Mr. Seymour, this must surely depend upon the nature of
the syllables,” said the vicar. “Pray excuse the interruption; but you
will admit that there must exist a great difference between the echo of
dactyles and spondees. Suppose an echo should be able to return ten
syllables; thus--
‘Tityre, tu patulæ recubans--’
I will be bound for it, that if you were to try its powers in slow
heavy spondees, as _monstrum horrendum_, a return of not more than four
or five syllables could be observed.”
“I will not dispute that point,” said Mr. Seymour.
Louisa here remarked that she had often heard of some very
extraordinary echoes in different parts of the world, to which her
father had not alluded; she mentioned, for instance, those which are
said to repeat the same sound several times in succession.
“From the explanation which I have already given of the nature of
echoes,” said Mr. Seymour, “it will be easily conceived that a vast
variety of effects may be produced by varying the form, the shape, the
distance, and the number of reflecting surfaces: and hence we hear of
various surprising echoes in different places. It is not difficult, for
instance, to understand the nature of compound, or tautological echoes;
in which case the expression of one _ha_ will appear like a laughter.
Addison mentions an extraordinary instance of this kind near Milan,
which will return the sound of a pistol fifty-six times.”
“I have understood that the echoes on the lakes of Killarney are of
this multiplied description,” said the vicar.
“They are particularly calculated to produce reflections of sound, from
the height of the mountains, and the expanse of water,” replied Mr.
Seymour, “which latter circumstance always assists the conveyance of
reflected, as well as direct sound. I believe that there is a certain
spot on the shore of Ross island, where the sound of a bugle produces
an echo which far exceeds any other to be met with amongst the lakes;
the first echo is returned from the castle, the second from the ruined
church of Aghadoe, the third from Mangerton, and afterwards innumerable
reverberations are distinguished, which, like the faded brilliancy of
an extremely multiplied reflection, are lost by distance and
repetition.”
“There is an admirable echo,” said the vicar, “behind my old college at
Cambridge; and often have I, while walking on the road to Chesterton,
on a calm evening, distinctly heard twelve repetitions of the voice.
Lord Bacon, if I remember correctly, mentions an instance of sixteen,
in some ruined church near Paris.”
“It was in the church of Pont-Charenton, on the Seine,” replied Mr.
Seymour; “in which place that great philosopher discovered the
inability of an echo to return the letter S, for having pronounced the
word _satan_, the echo replied _va-t-en_, which in French signifies
_away_; from which circumstance, the Parisians concluded, that some
guardian spirit prevented the walls of the sacred edifice from
pronouncing the name of _satan_.”
“And will not an echo repeat the letter S?” asked Louisa.
“Not always,” answered her father; “the hissing or sibilant noise of
the letter, when at the commencement of a word, is generally lost,
unless the echo be extremely perfect.”
The party now set off on their excursion to the valley. Mr. Seymour
disposed them in such situations as were best calculated to display the
powers of the echo, and to illustrate the several effects which he had
endeavoured to explain. The vicar performed his experiment with
dactyles and spondees, and was highly gratified to find that their
results proved, in a most satisfactory manner, the correctness of his
conjecture. The attention of Miss Villers was particularly directed to
the effect of the voice of Mrs. Seymour from the orchard gate, and
which, she said, convinced her that the sound she had heard on the
preceding evening must have arisen from the cause assigned to it.
After the party had fairly tired themselves by their converse with the
airy and unsubstantial being, they descended to the sandstone rocks,
which Mr. Seymour pointed out as the local habitation of the solitary
spirit. These were duly examined by Louisa and Tom, and their operation
as a reflecting screen was pointed out to them by their father. They
now returned into the geological temple; its singularly beautiful
pillars very naturally attracted the attention of Miss Villers, and she
expressed a wish that Mr. Seymour should describe the plan of their
construction; for it was very evident, as she said, from the
disposition of the specimens, that the arrangements had been directed
with some view to geological illustration. Mr. Seymour felt gratified
by this request, and promised to comply with her wishes, as soon as he
had finished the investigation of those laws by which the reflection of
sound was governed.
“Why, bless me!” exclaimed the vicar, “the revels of our airy companion
are ended; and I maintain, that nothing can be more appropriate than
the consideration of the objects for which Miss Villers has expressed
so much interest. In truth, the history of Echo is classically
associated with that of geology: by diving into the recesses of the
rock, we do but pursue her descent from air to earth; for you, no
doubt, remember that after she had been deprived of her loquacity by
Juno, she became enamoured of Narcissus, pined away, and was
transformed into stone.”[59]
“I cannot but admire the ingenuity with which you embellish every
subject with classical decorations,” replied Mr. Seymour. “You,
however, must well know that I require no such allurement on the
present occasion. I shall be most willing to afford Miss Villers the
information she requires, as soon as I have explained to my young
pupils the principle of the whispering gallery in St. Paul’s; as well
as some recreations which are indebted for their effects to the
reflection of sound.”
“I ought to apologise for the interruption I have occasioned,” said
Miss Villers; “but I was not, until this moment, aware of the extent to
which you intended to carry your illustrations.”
Mr. Seymour commenced with the subject of the “whispering gallery,” at
the foot of the dome of St. Paul’s cathedral; and in order to render
intelligible the manner in which sound is concentrated, and thereby
magnified in that hollow hemisphere, he produced a diagram, of which
the annexed cut is a copy.
[Illustration: Diagram of sound magnification.]
He explained it as follows:--
“M shows the situation of the mouth of the speaker, and E that of the
ear of the hearer. Now, since sound radiates in all directions, a part
of it will proceed directly from M to E, while other rays of it will
proceed from M to _u_, and from M to _z_, &c.; but the ray that
impinges upon _u_ will be reflected to E, while that which first
touches _z_ will be reflected to _y_, and from thence to E; and so of
all intermediate rays, which are omitted in the figure, to avoid
confusion. It is evident, therefore, that the sound at E will be much
stronger than if it had proceeded immediately from M without the
assistance of the dome; for, in that case, the rays at _z_ and _u_
would have proceeded in straight lines, and consequently could never
have arrived at the point E.”
“I have understood that a similar effect may be witnessed in the stone
recesses on Westminster-bridge,” said the vicar.
“That is the fact,” replied Mr. Seymour. “The recesses to which you
allude are semi-domes; and if a person whispers in the focus of one of
them, he will be distinctly heard by another stationed in the focus of
the opposite one. Two inanimate busts may be thus made to appear as if
holding a conversation, by placing them in the foci of two large
concave mirrors constructed of pasteboard, and arranged opposite to
each other; when a whisper uttered to the one will seem to proceed from
the other by the reflection of sound.”
Mr. Seymour now removed a shell from a group of corallines which
decorated a part of the temple, and desired Tom to place it to his ear.
“I hear a noise which appears to me to resemble that of the sea,” cried
Tom.
“Ay,” said the vicar, “and there is a popular belief that it is the
murmur of the sea, which the shell actually sends forth, betraying, as
it were, its marine origin.”
“And what produces the sound?” inquired Louisa.
“The interior of the shell merely concentrates, and thus magnifies the
sounds around us, so as to render them audible: a goblet applied to the
ear will be found to produce the same effect,” replied her father.
“I suppose it is upon the same principle that the speaking-trumpet is
made to convey sound to a distance,” remarked Louisa.
“Since sound radiates in all directions, it follows that, if such
radiation be prevented by confining it in tubes, it may be carried to a
great distance with very little diminution of its effect; and hence the
use and application of those trumpets, or tin speaking-pipes, which are
now commonly used for conveying intelligence from one part of a house
to another. The trumpet used by deaf persons acts on the same
principle; but as the voice enters the trumpet at the large instead of
the small end of the instrument, it is not so much confined, nor is the
sound so much increased.”
“I believe,” said Mrs. Seymour; “that the experiment exhibited some
time since in London under the title of the _Invisible Girl_, and which
excited such general curiosity, was discovered to depend upon an
arrangement of this kind.”
“I expected that you would allude to that exhibition,” said Mr.
Seymour; “and as I was anxious to provide my young pupils with some new
amusement, as a reward for their industry, I have directed Tom Plank to
construct the necessary apparatus for exhibiting and explaining the
deception. On our return to the lodge, I have no doubt we shall find
that every arrangement for the performance has been completed.”
Miss Villers was now gratified by a view of the more interesting
specimens in the geological temple. Mr. Seymour also explained the
design of the pillars which had so greatly excited her curiosity.
On the return of the party, Mr. Seymour found, as he had anticipated,
that the necessary apparatus for the experiment of the “Invisible
Girl!” had been duly arranged, and that Tom Plank was in attendance to
afford any assistance which might be farther required. We shall proceed
to describe all the visible mechanism, as it appeared to the children
on entering Mr. Seymour’s study, and of which we here present the
reader with a perspective sketch.
[Illustration: Apparatus for Invisible Girl experiment.]
It consisted of a wooden frame, not very unlike a bedstead, having four
upright posts, _a a a a_, and a cross-rail at top and bottom to
strengthen them. The frame thus constructed stood upon a low table, and
from the top of each of the four pillars sprang four bent brass wires,
which converged to the point _c_. From these wires a hollow copper ball
was suspended by ribands, so as to cut off all possible communication
with the frame. The globe was supposed to contain the invisible being,
as the voice apparently proceeded from the interior of it; and for this
purpose it was equipped with the mouths of four trumpets, placed around
it in a horizontal direction, and at right angles to each other, as
shown in the annexed section, in which the globe is represented in the
centre; _d d d d_ are the trumpets, and _b b b b_ the frame surrounding
them, at the distance of about half an inch from their mouths. Such as
we have described was the apparatus, which had been constructed under
the direction of Mr. Seymour, who informed the party that, if any of
them would ask a question of his little fairy, and direct the voice
into one of the trumpets, an answer would immediately be returned from
the ball.
[Illustration: Top of the Invisible Girl apparatus.]
“Let me interrogate her,” exclaimed Louisa, as she advanced towards the
railing. “Tell me, mysterious being, the name of the person who now
addresses you.”
“Miss Louisa Seymour,” answered a voice sufficiently audible to Louisa,
whose ear was near the mouth of the trumpet, and yet so distant and
feeble, that it appeared as if coming from a very diminutive being, and
thus heightened the deception. Each of the party successively asked
some question; and the surprise of the children may be more easily
imagined than described. Tom examined the ball, the trumpets, and the
framework; but he was unable to discover any clue by which he could
unravel the mystery. At length Mr. Seymour proceeded to the
explanation. He told them that the mechanism owed its effects to the
combined operation of two principles with which they were already
acquainted; the concentration and conveyance of sound by means of a
speaking-pipe, and its reflection from an appropriate surface so as to
change its apparent direction, by producing an artificial echo. He then
showed them the pipe which was concealed in one of the legs of the
frame, and explained in what manner the voice of Tom Plank, who had
been stationed in an adjoining room, was conveyed to the mouth of the
trumpet, and thence reflected to the ear of the observer. By means of
the annexed section, we shall hope to render this subject as
intelligible to our readers, as did Mr. Seymour to his little pupils.
[Illustration: Side view of Invisible Girl apparatus, with secret pipe
shown.]
_b b_ represent two of the legs of the frame, one of which, as well as
half the rail, is made into a tube, the end of which opens immediately
opposite to the centre of the trumpet. This hole is very small, and
concealed by mouldings; the other end communicates by a tin pipe, _p
p_, which passes, in a concealed manner, along the floor of the room,
into an adjoining closet, where the confederate is concealed. It is
evident that any sound, directed into the mouth of the trumpet, will be
immediately reflected back to the orifice of the tube, and distinctly
heard by a person who places his ear to the mouth of the funnel _m_;
while the answer returned by him, travelling along the tin funnel, _p
p_, will issue from its concealed orifice, and striking upon the
concave surface of the trumpet, be returned to the ear as an echo, and
thus appear as if it had proceeded from the interior of the ball.
The vicar observed, “that this deception of the _Invisible Girl_, which
had formerly created so much interest, was little more than the revival
of the old and well-known mechanism of the _speaking bust_, which
consisted of a tube, from the mouth of a bust, leading to a confederate
in an adjoining room, and of another tube to the same place, ending in
the ear of the figure; by the latter of which, a sound whispered in the
ear of the bust was immediately carried to the confederate, who
instantly returned an answer by the other tube, ending in the mouth of
the figure, which therefore appeared to utter it. The Invisible Girl,”
continued the vicar, “evidently only differs from that contrivance in
this single circumstance, that an artificial echo is produced by means
of the trumpet, and thus the sound no longer appears to proceed in its
original direction.”
“Your remark is perfectly correct, my dear vicar,” said Mr. Seymour.
Tom Plank, with an air of self-satisfaction, at this moment emerged
from his retreat, and enquired whether his performance had not met with
the approbation of his employer.
“Gentlemen,” said Tom Plank, “as I am now fully satisfied that any plan
of propelling live and dead luggage through funnels can never succeed,
I propose to employ tubes for conveying sounds to a great distance, so
as to do away with the use of telegraphs?”
“Why that plan is more practicable, but less novel, than the one you
have just abandoned,” answered Mr. Seymour. “At the latter end of the
last century, a man of the name of Gautier conceived a method of
transmitting articulate sounds to an immense distance. He proposed the
construction of horizontal tunnels that should widen at their
extremities, by means of which the ticking of a watch might be heard
more distinctly at the distance of two hundred feet than when placed
close to the ear. I think he calculated that a succession of such
tunnels would transmit a verbal message nine hundred miles in an
hour.”(50)
“Only think of that!” ejaculated Tom Plank; “to make a communication
from London to Edinburgh in about twenty-five minutes!”
“True, my friend; but what would you say, were I to suggest a method of
communicating information to any distance without the loss even of a
single second of time.”(51)
“There now,” cried the vicar, “you have supplied Tom Plank with some
fresh barm to set his brains working.”
“He is an indefatigable fellow, I must allow,” said Mr. Seymour.
After this discourse the vicar rose from his seat, and on walking
across the room, the creaking of his shoes excited the attention of Mr.
Seymour, who, with his accustomed gaiety, observed, that “the vicar had
music in his _sole_.”
“Mr. Seymour!” exclaimed Mr. Twaddleton, with a look which we should in
vain endeavour to describe, “the infirmity of my shoes, _crepitus
crepidæ_, is at all events sanctioned by high antiquity; for we are
told by Philostratus, in his Epistles, that Vulcan, being jealous of
Venus, made her creaking shoes, in order that he might hear whenever
she stirred.”
So ludicrous an appeal to antiquity would have overcome Heraclitus
himself, no wonder then that the whole party enjoyed a hearty laugh at
the worthy vicar’s expense.
“Well, Mr. Twaddleton, if, as you say, I have brought down philosophy
to account for the most familiar occurrences, it is but just that I
should return the compliment, by declaring that you are equally
prepared to throw a classical interest around the humblest as well as
the most dignified subject, _à capite usque ad calcem_,” observed Mr.
Seymour.
“Now, Tom, as you have so lately been instructed in the different
sources of sound, do tell your good friend, the vicar, the cause of the
creaking of his shoes,” said his father.
“The dryness of the leather, I suppose,” answered the young philosopher.
“A certain state of dryness is certainly a necessary condition, or else
the cohesion between the inner and outer sole would exclude the air.
Correctly speaking, the creaking depends upon the sudden compression of
the air contained between the two surfaces of leather; just as a sound
is produced by the clapping of the hands by the air thus set in
vibration. Shoes with single soles, therefore, never creak, and by
interposing a piece of oil-silk between the two soles, you will so far
ensure the contact of their surfaces as to obviate the sound,” said Mr.
Seymour.
“That is at all events a piece of practical philosophy worth knowing;
and I shall accordingly instruct my operator, Jerry Styles, upon this
point,” observed the vicar.
“So you see, my dear sir, I am no bad shoemaker, although I have never
yet made a shoe,” said Mr. Seymour.
“To be sure--to be sure,” exclaimed the vicar; “for as Horace has it--
----“Sapiens crepidas sibi nunquam
Nec soleas fecit: Sutor tamen est sapiens.”[60]
“You never made a happier quotation,” exclaimed Mr. Seymour.
“I have only one other remark to make,” continued he, “which the
consideration of this subject has very naturally suggested--that the
various strange sounds, which have from time to time alarmed the
superstitious, may be readily explained upon the simple principles we
have been discussing. I well remember a whole family having been thrown
into a state of terror, by a mysterious sound which regularly recurred
every evening; when it was at length discovered to arise from the
crawling of snails over the window; their slimy surfaces, as they moved
along, produced a friction, which occasioned a vibration of the glass.”
“And I never recall to my recollection, without some degree of terror,”
said the vicar, “the night I passed in an old oaken chamber which had
the reputation of being haunted. A bright fire cheerfully blazed in the
grate as I entered the apartment, and casting its ruddy light around,
in some measure dissipated the prejudice which had been raised to the
disparagement of my dormitory; but awaking in the night, my fire was
out, and a succession of the most extraordinary noises I ever heard
assailed me.”
“All which are easily explicable,” said Mr. Seymour. “The old oaken
materials were expanded by the heat of your fire, and on the apartment
cooling, they again contracted, and gave origin to all the sounds you
describe.”
“How unsparingly does science clip the wings of imagination!” observed
Miss Villers.
The party now dispersed. Miss Villers retired into the drawing-room, to
afford Louisa some musical instruction; the vicar took his departure
for the sake of visiting a sick parishioner; and Major Snapwell to make
arrangements for an important event, with the nature of which the
reader will very shortly be made acquainted.
-----
Footnote 57:
“Murænæ optimæ flutæ sunt in Sicilia.” _Varr. R. R._ ii. 6. 2.
Footnote 58:
The reader is requested to turn to page 174; for all that is there
said respecting the principle of _reflected_ motion will apply to the
theory of the echo.
Footnote 59:
Ovid’s Metamorph. 3. 358.
Footnote 60:
“For though the wise nor shoes nor slippers made,
He’s yet a skilful shoemaker by trade.”
_Hor. Sat. 3 Lib. 1._
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