Mower County transcript. [volume] (Lansing, Minn.) 1868-1915, 1874-03-12
FOG SIGNALS.


| m1sey-Frof. Tynaal's Experiments.
From the Now York Herald.
Prof. Tyndall has recently boon 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 aZe Of great interest.
In a.lecture delivered before the Roy
nj Institution on the 10th ult., he an
nounced some of his conclusions, ar
rived At after observations extending
over period of ak months and during
many vicissitudes of wind and weather.
Asfar az We can gather from brief &C.
count Of his lecture in the London Ma
ti0nl Magazine il appears that the dis.
anceSesNAilk4og signals are audible
on different days vary in most remark
able manner. He is reported as saying
that if the sound of gun can he heard
on fine, calm day at = distance of 10
miles, the experiments show that there
similar day the sound should be heard
At three or four, miles. On the 10th
and Goth Of May it seemed to be dem
onstrated to a certainty that the sound
of gun could be distinguished fur
Their than that OF a trumpet. And yet
on succeeding days the trumpet was
audible ut several miles distance, and
the gun inaudible. Again, on June Is,
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 II miles dis
tant, while on some clear days they
were inaudible ut very much shorter
distances.
The uncertainty and variability in
the serial 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 of
ideas now prevailing on this subject.
Prof. Tyndalls labors would seem to
show that our fog signals are not to be
relied on for q distance exceeding three
miles, and, perhaps, under some serial
conditions, less.
The homogeneity of the air strata
and their relatively tranquil condition,
it is known greatly affect the intensity
of sound, and permit the sonorous
waves to be propagated without losing
their amplitude by reflection. # there
is an irregular oommixture of light and
dense air, then the sound waves are re-
aected back from the interposing walls
of the denser media. This principle,
which has been clearly brought out by
Prof. Lockyer, was strikingly verified
on the Sd Of July, when the air seemed
to be singularly lacking in homegenei-
ty, and Prof. TyndaQ found-notwith-
standing it was clear, calm and sunny
day-that nothing at all was audible at
three miles. It was proved ON going to
the place on shore where the signals
were sounding that echoes of Is Sec
onds' duration came back from the air
space in front, showing what had be-
come of intransmissible sound which
was lost to the listeners only three miles
of. In this singular instance the dense
air had been opaque to the sound, and
the sonorous wave breaking against it
was arrested as wave of the sea break
ing on rock. ..E> /.