The Milan exchange. (Milan, Gibson County, Tenn.) 1874-1978, 1874-04-30
Singular Properties Of Sound.

singular Properties OF Sound.
The Scientific american gives an inter
esting resume of Prof. Tyndall's research
es into the performance of various kinds
OF signals used on rocky coasts to warn
vessels, when the fog prevails. "The
sound-pl oducing apparatus consisted in
two large brass trumpets, ii feet long and
blown by an air pressure of Is pounds,
two locomotive whistles, and an Is pound
er gun fired with a three pound charge OF
powder. Professor Tyndall embarked
aboard small steamer. which, under his
direction, was moved from point to point
from the locality of the sounding instru-
ments, South Foreland Cliff, near Dover.
The observations were carried on over sew
eral days, with varying results some OF
! which the investigator found himself at a
loss to explain. Thus on one day the dis
lance at which the sound could be heard
was 81 miles; on the next day 10 miles.
The former day the wind was i'm the direc-
ton of the sound; on the latter. the wind
was opposed. Again. on another occa-
sion it was noted that the sounds were not
impaired during the continuance of rain
though the state of the atmosphere, ac-
cording to expressed opinions, should
have deadened them. A clear atmosphere
has been eXtolled as the best for sound
but the noise of the horns, saws Professor
Tyndall, was heard l22 miles dead to
windward of the cliff and while the latter
was obscured by a thick haze. 1t was a
curious and incomprehensible fact that,
under these conditions, the sound ranged
at least twice as far as it had done on days
when neither haze nor wind was there to
interfere with it. To add to the perpleXity
of the investigator, subsequently to the OBJ
servation of the above phenomena, on a
perfectly bright, clear day, with smooth
sea and no wind, not vestige of sound of
either horn, whistle, or gun could be de-
tected at distance of two miles. He says
he stood amazed and confounded,' for he
saw no palpable clue to the solution of
the problem. 1t was Il case where ones
senses are of no use, where they and all
the philosophical instruments in the world
cannot be of the least assistance. How,
then, is it to be answered? ?" After much
thought, the Professor hit upon the idea
that possibly the sound might be obstruct-
ed merely by spaces of varying moisture in
the air, just as light is quenched in snow
ball. :" A SNOWFALL is not OFFICIALLY con-
tinuous ice, but an aggregate of grains of
ice, and the light which falls upon the
9AAO"s bthi- lNANNbCd llllllllilS SUI
faces of the snow granules, fails to pene-
trate the snow to any depth. Thus by the
mixture of air and ice-twO transparent
substances-we produce a substance near
ly as imperyiOus TO light as a really Opaque
one. And this is equally true of foam,
clouds and all transparent substances in
powder" Thus reasoning, Prof. Tyndall
became conscious Of the exceeding power
of the sun beating against his back and
heating near objects. Here was clue,
and the rapiditv with which he followed il
is well shown in the short, terse sentences
which sum up a complete explanation of
the mystery. Beams of equal power
says the Professor, were falling on the
sea, and must have produced copious evap-
Grafton. That the vapOr generated should
so rise and mingle with the air as to form
an absolutely homogeneous mixture, /
considered in the highest degree improb-
able. 1t would be sure, | thought, to
streak and mOttle the atmosphere with
spaces, in which the air would be in differ
ent degrees sa urated, or, it might be, dis
placed by the vapOr. At the limiting sur
faces OF these SPACES, though visible, we
should have the conditions necessary to
the production of partial echoes and the
waste of sound Following up
this mental conclusion with experimental
test, it was found fully verified. A cloud
coming before the sun checked the prOduc-
ton of vapor, so that sounds, before inau-
dible at three miles distance, became clear
ly heard. Again, as the sun went down,
the signals became louder and further re-
to such an extent, it is stated,
that at 6 p. IN. the sound had risen to more
than forty-fold the intensity which it pos
seSsed at , in the afternoon"