The Massachusetts spy, and Worcester County advertiser. [volume] ([Worcester, Mass.]) 1825-1831, 1831-06-15

PROPERTIES OF SOUND. When sound is stop
90 IN It's progress by an even surface, such as
wall, the side of house, the face of a rock, or
the side of hill, it is reflected or driven back
exactly like light from mirror; and the OBJ
! server, who emlts the sound, will hear the re-
nected sound or sch0, some time after the orig
maj sound was emitted. If person, for exam
pie, stands opposite the face of rock, at the
distance of 1890 feet, and fires pistol, the
sound will take one second to reach the rock,
and when reflected from it, il will take another
second to return to the observer, so that the
een0 VIII be heard exactly tao0 seconds after
the discharge of the pistol. Hence we may de-
termine the distance in feet of the body which
occasions the echo, by multiplying 1890 feet by
nan the number of seconds between the sound
ana lis echo. In order to hear the echo most
distinctly, the person must always be directly
opposite the middle of the wall or obstruction
which reflects the sound If the place where
tho sound is made is different from the place of
the. observer who is TO hear it, then the ear of
the observer must be as distant on one side from
the point directly opposite the middle of the
wall as the place of the sound is distan. from it
on the other or, to speak more technically,
sound is reflected like light, so that the angle
OF incidence, or the INCLINATION at which the
sound falls upon the wall, is equal to the anglo
Of reflection, or the inclination at which the
sound is returned from the wall We have had
occasion to observe very fine proof of this
property of sound in the circular turn of a gar
den wall, nearly mile distant from wier over
river. When the air is pure and the wind
favorable, the rushing sound of the water is re.
Elected from the hollow surface of the wall; and
concentrated in focus like the rays of light, |
and the ear can easily discover the point where |
the sound is most intense. Various rsmarka. !
bic echoes, and some not very credible, have |
been described by different authors Doct Plot |
mentions an echo in Woodstock Park, which !
repeats seventeen sylables by day, and twenty
by night. The famous echo at the MARQUIS
Simoneta's villa near Milan has been described
both by Addison and Keysler. According to
the last of these travellers, it is occasoned
by the reflection of the voice between the op-
posite paraeied wings of the building, which
are fity-eight PAGES from each other, without
any windows or doors, and perpendicular to the
main body of the building. The repetition of
the sound dwells chiefly on the last syllable
mans voice is repeated above forty times,
and the report of pistol above sixty times but
the repetitions rapid that it Is difficult to
number them, unless it be early in the morning
or in a catm, still evening. curious example
OF an oblique eche, not heard by the person who
emlts the sound, is described in the " Memoirs
OF the Academy of Sciences" as existing at
Genofay, near Rouen. A person singing hears
only his own direct voice, while those who lis.
ten hear only the echo which sometimes Sc ems
TO approach, and at other times to recede from
the ear; one person hears single voice, an
other several voices one hears the echo on the
right, and another on the left-the effect con-
stantly changing with the position of the OBJ.
server One of the most remarkable echoes of
which we have read is that which Dr. Birch de-
scribes as existing in Argylshre. When per-
son at proper distance played eight or ten
notes on 4 trumpet, they were correctly re-
peated, but third lower; after short silence,
another repetition was heard in yet lower
tone, and after another short interval, they
were repeated third time in tone lower still.
HerSchel's Treatise on Sound.