Various remarkable echoes, and some not very credible, have been
described by different authors. Dr. Plott mentions an echo in Woodstock
Park, which repeats seventeen syllables by day and twenty by night.
The famous echo at the Marquess Simonetta's villa, near Milan, has been
described both by Addison and Keysler. According to the last of these
travellers, it is occasioned by the reflection of the voice between the
opposite parallel wings of the building, which are fifty-eight paces
from each other, without any windows or doors, and perpendicularly
to the main body of the building. The repetition of the sound dwells
chiefly on the last syllable. A man's voice is repeated about forty
times, and the report of a pistol about sixty times; but the repetitions
are so rapid, that it is difficult to number them, unless it be early in
the morning, or in a calm, still evening.
A curious example of an oblique echo, not heard by the person who emits
the sound, is described in the "Memoirs of the Academy of Sciences" as
existing at Genefay, near Rouen. A person singing hears only his own
direct voice, while those who listen hear only the echo, which sometimes
seems to approach, and at other times to recede from, the ear; one
person hears a single voice, another several voices; one hears the echo
on the right, and another on the left--the effect constantly changing
with the position of the observer.
One of the most remarkable echoes of which we have read is that which
Dr. Birch describes as existing at Roseneath, in Argyllshire. When a
person at a proper distance played eight or ten notes on a trumpet, they
were correctly repeated, but a third lower; after a short silence,
another repetition was heard in a yet lower tone, and alter another
short interval, they were repeated a third time in a tone lower still.
We extract the following account of two very interesting echoes from Mr.
Herschell's work:--
"In the cathedral of Girgenti, in Sicily, the slightest whisper is borne
with perfect distinctness from the great western door to the cornice
behind the high altar, a distance of 250 feet. By a most unlucky
coincidence, the precise focus of divergence at the former station was
chosen for the place of the confessional. Secrets never intended for the
public ear thus became known, to the dismay of the confessors and the
scandal of the people, by the resort of the curious to the opposite
point (which seems to have been discovered accidentally), till at length
one listener, having had his curiosity somewhat overgratified by hearing
his wife's avowal of her own infidelity, this tell-tale peculiarity
became generally known, and the confessional was removed.[2]
"Beneath the Suspension Bridge across the Menai Strait in Wales, close
to one of the main piers, is a remarkably fine echo. The sound of a blow
on the pier with a hammer is returned in succession from each of the
cross-beams which support the road-way, and from the opposite pier at a
distance of 576 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 described:--The first return is sharp and
strong from the road-way overhead; 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 184 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 proportionably 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."
In treating the important subject of echoes in churches and public
buildings, Mr. Herschell has exposed several prevailing errors, and laid
down several useful principles, which merit the particular attention of
the architect. In small buildings the echo is not distinguishable from
the principal sound, and therefore serves only to strengthen it; but
in very large buildings, where the original sound and its echo are
distinctly separated, the effect is highly disagreeable. In cathedrals,
this bad effect is diminished by reading the service in a monotonous
chant, in consequence of which the voice is blended in the same sound
with its echo. In musical performances, however, this resource is not
available. When _ten_ notes are executed in a single second, as in
many pieces of modern music, the echo, in the direction of the length of
a room fifty-five feet long, will exactly throw the second reverberation
of each note on the principal sound of the following note, wherever the
auditor is placed. Under such circumstances, therefore, the performers
should be stationed in the middle of the apartment.--_Ibid._
[2] Travels through Sicily and the Lipari Islands in the month of
December, 1824. By a Naval Officer. 1 vol. 8vo. London, 1827.
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