The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1874-05-18

Not long since Professor Tyndall, in behalf
of his government, conducted q series OF
acoustic experiments in British waters to test
the transmissibility Of fog signals. He an
nounced more recently some important con.
illusions to which his Investigations had led
him, and these results have been widely
quoted as showing the unreliability of the
sound signals employed at modern light
houses and coastguard stations. The expla-
Visible vapor, especially on clear. hot days,
rendered the air acoustically Opaque, the
vnpor acting as q screen or wall to arrest OF
divert the sound-wave.
Professor Reynolds, Of Manchester, has
given practical and useful REPUTATION to this
hasty theory by experiments which show that
the sound-waves are otherwise reflected
and which suggest how the phonio coast
signals may be rendered more avail
able for fog warnings. Professor Reynolds
experiments show that the sounds are not
lost even when proceeding against the wind.
but are lifted up of the ground The effect
of wind and rough surfaces in lifting sounda
accounts for the capricious variations in tha
intensity with which they are audible at differ.
ent times, and it gives the reason why instinc-
lively we elevate church bells and platforms
when the sounds are to be heard at great dis
tances. This experimental research also proves
that sounds are lifted upward in the air in
proportion as the upward diminution of tenn
perature increases. The acoustic rays divergs
toward the clouds in curves, varying in their
sharpness as the sky is clear or cloudy, the re-
fraction being twice as great on bright, hot
days as in cool, cloudy weather.
These conclusions are corroborated by the
balloon experiments Of Glaisher, Flammarion
and Others, who at very high points distinctly
heard the whistle Of the locomotive miles
below, showing that the sound-wave was not
broken up or transmitted horizontally, but
vertically. Atan elevation Of ten thousand feet
over Wolverhampton Glaisher heard the dis
charge Of q gun, and the same sound twenty
thousand feet above Birmingham ; while alss
he mentions hearing the barking of dog at .
vertical distance Of two miles.
The audibility Of the steam siren and fog
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of vital importance to the seaman on our
long Atlantic coast and on the lakes, where
the seashore is SO often shrouded in fog and
mist. The able and thorough paper Of Pro-
fessor Reynolds in bringing to light the real
philosophy Of the aerial refraction of sound
suggests the means of making the fog signals
reliable. It is only necessary to elevate tho
source of the sound, or the sound receiver, or
both, above the ground to insure its trans
mission. A vertical difference Of thirty feet
makes the sound go at least quarter of .
mile further, and this increase on foggy
coast would suffice to save steamship rum
ming at full speed on the rocks. The distance
to which the warning is conveyed across tho
waters would be doubled if the lookout on the
ship were stationed in the rigging.
Our lighthouse authorities and scientists
would do well to prosecute such researches
and avail themselves Of the practical benefits
they afford.