River Falls journal. [volume] (River Falls, Pierce County, Wis.) 1872-2019, 1874-03-17
roc SIGNALS.
Are They Reliablc--The Subject n Little
Mi-fy-~ProG Tyndalfs Experiments.

Are They Reliable--The Subject " Little
Mi-'y-Proh Tyndall's Experiments.
From the New York Herald.
Prof. Tyndall has recently been con
Quoting series Of experiments to test
the acoustic character of fog signals.
His experiments have been undertaken
in connection with the labors and un-
der the co-supervision of the Trinity
House Committee, and the reported re-
suits are of great interest.
In lecture delivered before the Roy
al Institution on the 10th ult, he an,
nounced some of his conclusions, ar
rived at after observations extending
over period of six months and during
many vicissitudes of wind and weather.
As far as we can gather from brief ac-
count of his lecture in the London Ma
tional Magazine il appears that the dis
tanoes at which fog signals are audible
on different days vary in most remark
able manner. He is reported as saying
that if the sound of gun can be heard
on fine, calm day at a distance of 10
miles, the experiments show that there
Is no reason why on another apparently
similar day the sound should be heard
at three or four miles. On the 18th
and 10th of May it seemed to be dem
onstrated to a certainty that the sound
of gun could be distinguished fur
ther than that of trumpet. And yet
on succeeding days the trumpet was
audible at several miles distance, and
the gun inaudible. Again, ON June 26,
with the wind favorable, no sounds were
perceived at six miles, while the day
following, with the wind opposed, they
were clearly heard nine miles. Once,
during thick haze, which hid the land
from view and limited the visible hori-
zon to one-and-a-half miles, the sounds
were distinguishable over IL miles dis.
tant, while on some clear days they
were inaudible at very much shorter
distances.
The uncertainty and variability il
the erial transmission of signal sounds
thus brought to light. are Of immediate
and vital Importance to the mariner
and demand an exhaustive investiga
ton, as well as thorough revision oil
ideas now prevailing on this subject
Prof. Tyndalls labors would seem t
show that our fog signals aie hot TO be-
relied on Tor distance exceeding three
miles, and, perhaps, under some eria
conditions, less.
The homogeneity of the air STRAIT,
and their relatively tranquil condition
1t is known greatly affect the intensity
of sound, and permit the sonorou
: waves to be propagated without losing
their amplitude by reflection II ther,
is an irregular eommixture Of light ant
dense aif, then the sound waves are re
Elected back from the interposirg WALL
of the denser media. This principle
which has been clearly brought out b,
Prof. Lockyer, was strikingly verified
on the 3D. of July, when the air seemed
to be singularly lacking in homegenei
| ~ and Prof. Iyndall found-notwith
standing it was a clear, calm and sum,
day-that nothing at all was audible a
three miles. 1t was proved on going t
the place on shore where the signals
were sounding that echoes of 10 see
onds' duration came back from the all
space in front, showing what had be
come of intransmissible sound which
was lost to the listeners only three mile;
of. In this singular instance the dense
AIR had been Opaque to the sound, anC
the sonorous wave breaking against il
was arrested as a wave of the sea break
ing on a rock