Mower County transcript. [volume] (Lansing, Minn.) 1868-1915, 1874-03-12
FOG SIGNALS.
Arc They Rclinhlc-Thc Subject a Little
Nftafy-Prof. Tyudall's Experiments.

NItaty-PrOC. TSudall's Experiments.
From til" Now York Herald.
Prof. Tyndnll has recently been con-
Quoting Il series Of experiments to test
tho 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 grcnt interest.
In u lecture delivered before tho Roy
nj Institution on the 10th ult., he an
nounced some of his conclusions, ar
rived at after observations extending
over q period of six months and during
many vicissitudes of wind ind weather.
As far rs We can gather from brief &C
count of his lecture in the London Ma
tional Magazine it appears that the dis
t"nces At which fog signals are audible
on different days vary in most remark
able manner: He is reported rs saying
that if the sound Of II gun can be heard
on fine, calm day Mt distance Of 10
miles, the experiments show TINT there
is no reason why Oh another apparently
similar day the sound should I've heard
at three or four miles. On the 10Th
AMI Goth Of May it seemed to DO dom
onstrate,l to certainty that the sound
of gun could be distinguished fur
ther 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 26,
with the wind favorable, no sounds were
perceived Mt 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-
ION to one and-a-half miles, the sounds
were distinguishable over IL miles dis
tant, while ON some clear days they
were inaudible Mt very much shorter
distances.
The uncertainty and variability in
the aerial transmission of signal sounds,
thus brought to light, are of immediate
and vital importance to the mariner,
ton, us we'll as thorough revision of
ideas now prevailing on this subject.
Prof. Tyndall's labors would seem to
show that our fog signals are not to be
relied on for n distance exceeding three
miles, and, perhaps, under some aerial
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. If there
is an irregular commixture of light and
dense air, then the sound waves are re-
Elected 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. Tyndall found-notwith-
standing it was a clear, calm and sunny
day-that nothing at all was audible at
three miles. 1t 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
off. 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.