Echoes [pp. 369-370]

1869.] LITEBA TUBL SCIENCJJ AND AI?R 36
E E CHOES.
POPULAR science has long since made us familiar with the fact
that the sounds which we hear with our ear are in noways dif ferent in their nature from the colors which we see with our eye. Both
are produced alike by the vibrations which they cause in the air, and
loth are subject to similar laws. Thus, as the rays of light are re flected by solid surfaces, especially when the latter are smooth and
highly polished, so sounds also are apt to be returned from the sur faces of certain bodies. Soft or elastic substances give way easily
to sounds, and hence prevent their being reflected clearly; while hard
and rigid substances return them more or less perfectly. This reflec tion of sounds we call echo.
Good echoes are rare, for many reasons. In the first place, the
speaker must be at a certain distance from the reflecting surface, in
order to hear the return of the sound he produces, because sounds
travel slowly, at least in comparison with the waves of light. As we
cannot very well utter mnore than five syllables in the second, and as
sound requires the tenth part of a second to reach a distance of a
hundred feet, the speaker must be, at the very least, a hundred feet
from the reflecting wall, in order to hear the echo of a single syllable.
If he were nearer, the echo and his own voice would intermingle, and
both become confused. In all cases, therefore, the distance must be
great enough to allow the sound to go and return between the speaker
and the echoing surface while the word or the syllable is uttered which
is to be heard a second time. In the second place, no more syllables
must be spoken than can be repeated by the echo, or the first sounds
of the echo will be covered up by the last syllables uttered. This
circumstance is productive of some of the sportive answers elicited
from certain localities. On the Rhine it is customary for boatmen to
entertain travellers by asking a well-known rock, "Who is burgomaster of Oberwesel?" to which the answer comes, "Esel "-the
German word for donkey. Cardanus related the story of his
Italian countryman, who, unable to find the ford across a river, exclaimed, "Oh!" and immediately heard another "Oh!" in reply.
Thinking that he was not alone, he asked, "Onde devo passar?"
(Where must I cross?) to which the answer came, "Passa!" (Cross!)
He asked again, " Qui?" (Here?) and the reply was, " Qui!"
(Here!) The man saw, however, that the place before him was evidently of the most dangerous kind, and therefore inquired once more,
"Devo passar qui?" (Must I cross here?) and, when the answer
came-" Passa qui!" (Cross here!)-he became convinced that au
evil spirit was mocking him, in order to destroy him, and ran away
as fast as he could.
If there should be more than one such reflecting surface near the
speaker, the result would, of course, be a repeated echo. The sound,
then, either returns from each wall, or passes from one to the other
before coming back to the ear. The greater the distance, the fainter
the echo becomes, because sound loses on the way a part of its intensity; hence the answering voice grows apparently weaker and
weaker, and finally dies away in the distance. If the distance between the repeating surfaces is not the same in each case, but diminishes gradually, then the successive repetitions cover each other, in
part, and become shorter in the same proportion. Such an arrangement, artificially provided for, produced the well-known answer to
the question,
"Tibi vero gratias agam quo clamore?" (In what manner shall I
thank you?) "Clamore-amore-more-ore-re" (With the voice-with love
-with manner with the mouth-with deeds).
We all have had our hearty laugh at the Irishman who boasted of
the Emerald Isle that it had an echo superior to all others on earth,
because, when you asked it: "How do you do?" it answered, politely: "Very well, thank you." And yet the great German master
of acoustics, Kircher, succeeded actually in producing an echo which
answered questions, not by repetition, but by a change of words. In
the neighborhood of Rome he discovered an angle in the ancient walls
of the city, so constructed that the voice of a speaker placed in front
of it did not strike the opposite side, but a place round a corner, and
was consequently completely lost. There, hid by the angle in the
walls, stood his accomplice, who replied to the question, and, as the
sound of his voice pursued the same course, it reached the ear of the
first speaker in the precise manner of an echo; and the man who
asked:" Quod tibi nomen?" (What is your name?) heard, to his
utter amazement, the echo reply, "Constantius." The same author
quaintly suggests an elaborate plan, based upon actual experiments
made in the churches of St. Peter and St. James, at Rome, by which
the echo in great cathedrals could be ingeniously employed to improve
the effect of sacred music, and to fill up pauses by graceful repe titions.
The echo dwells in the country as well as in town, and hence the
Daughter of the Voice, as the ancient Hebrews used to call it,
strengthens the bonds that unite man with Nature. The woods and
the torrents, the mountains and the rocks-all repeat the voice of
their master, now in sport, and now apparently in terror; and Virgil
could point out how the huntsman does not sing to deaf matter,
as the forests reply to his voice:
"Non canimus surdis, respondent omnia silvase."
The echo thus supplied by forests depends probably more on the
grouping of the trees than on the masses of wood and foliage. This
is proved by experience. Thus Gay Vernon states that, in his youth,
he loved to hear a beautiful echo, produced apparently by the build ings of a mill; but, when he returned, after a prolonged absence in
Paris, he looked for his echo, and found it no longer. The buildings
were still there; but a few trees that formerly surrounded them had
been cut dowN. In the same manner, the echo produced on the plain
of MIontrouge, south of Paris, depended, not on a long brick wall, to
which it was generally ascribed, but to a row of trees planted in front.
The echo was only heard under and near the trees, while it disap peared close by the wall; and, when the ear was placed on the trunks
of the trees, they could be felt to tremble under the influence of the
speaker's voice, while the wall remained motiorless.
Houses have the peculiarity, as yet unexplained, that they will give
an echo only when either the doors are open and the windows closed,
or the windows open and the doors closed. It is stranger still that
many subterranean rooms only repeat certain musical notes. In the
old college building of Harcourt, where careful experiments were made
by a savant, the curious result was observed, that, when a man was
placed in the centre of the court-yard, the deep notes of his voice came
back from one direction, and the higher ones from another. Hence
the impression that the nymph, jilted by f4ir Narcissus, and bequeathing to Nature only her voice, still subject to the will of others, is to
this day as capricious as her sex-full of strange whims and unaccountable changes. At times the fair sprite revenges herself on the
sex of her cruel lover. Thus the story goes, that an Englishman,
travelling in Italy, met there with an echo which delighted him so
much that he bought it for a high price. It was produced by an isolated house; hence he thought he was quite sure of his purchase,
when he ordered every stone to be carefully numbered, packed, and
carried to England, where the building was reerected in precisely the
same manner, and at the same distance from other houses or hills as
before. When all was ready, he invited a large company, promising
to treat them, at dessert, to the finest echo they had ever heard. They
ate well and drank well, and at last the host declared his intention to
introduce them to his great treasure. He sent for his box of pistols,
loaded them, and fired the first from the open window. Alas! not a
sound came back. Without saying a word, he took the second pistol
and shot himself. It has never been ascertained why the echo declined to answer in England as it had done in Italy.
Even the clouds are at times disposed to furnish an echo. When
the Bureau of Longitudes in Paris determined the velocity of sound, by
observing the firing of cannon, a powerful echo was heard whenever
clouds overhung the station. It need not be mentioned here, that
thunder itself is but the effect of an often-repeated echo between
the storm-laden cloud and the surface of the earth. Aeronauts, on the
contrary, hear their own voices reecho from the earth, and this forms
the only tie that still binds them to their home long after they have
apparently severed every other bond.
While some echoes are famous for the distinctness with which
they repeat sounds, others have become celebrated for the number of
times with which they repeat. At a place where a small river, the
Nahe, empties into the Rhine, near Bingen, a word is distinctly repeated seventeen times, and, what is perhaps the most curious feature,
the echo does not sound each time alike, but is now loud and now
low, now near and now distant, and different persons fancy they
hear it from different sides. It is customary to fI-e a pistol for
the amusement of the passengers on board the steamboats as they
1869.]
LIT.E-RA TURE~, SCIE~CE, A-D ART.
369