New-York tribune., 1876-10-24
roc SIGNALS,
city

The steam siren at the Centennial EXhibi-
tion has given to many thousands of people
from the interior States some notion OF the
means that are taken on our COASTS to warn
vessels approaching during fog. To many OF
these inland citizens "a heavy sea-tOg such as
now envclops our Atlantic cities is perhaps
almost ah much a novelty as is the noisy fog
horn. Crossing some ferry where even
voyage of less than a mile between familiar
river fronts is all at once attended
with difficulty and delay if not with
danger they may gain some faint conception
OF the pcrls that encompass an ocean steamer
off shore when heavy fogs close III upon 1t.
Sun and moon and stars and the friendly
beams of the lighthouse are alike cut OIL by
the enshrOuding mist. Guess-work must sup
ply the place of observation, to determine
whether the vessel is nearing dangerous rocks
or has yet abundant sea-roOm. At such
moment the hOarse song OF the fOg-slren Is a
welcome note to the mariner; he regards 1t
with very different feelings from those OF the
crowd of visitors at the Exhibition who when
the blast is opened hasten to stick their lin
gers III their ears.
American fog signals, especially those in
vented in recent years, are far superior to the
old contriyances of bell ringing and gun
firing. Most of the more important improve
ments have been adopted by the L. S. Light
house Board, in consequence of an elaborate
series of experiments in which Prof Henry
of Washington has borne the chief
burden of direction. Though practi-
cal in their results, the researches have
been thoroughly scientific in their character.
Within the present year Prof. Henry's expert
mcnts of this kind have developed new and
remarkable facts which have practical bear
ing Such is, for instance, the discovery that
sound is not reflected as light is by mirror
of appropriate shape, in straight beams to
indefinite distances, but begins TO spread IN
all directions as it travels. From this 1t re-
suits that the system of placing mirrors behind
fog signals is of little use. The sound at
distance of four miles is entirely scattered,
and can be heard as well behind the mirror or
the fog-trumpet as in front of 1t. The sound
appears 10 be echoed from all around the
horizon. These ocean echoes have been pro-
foundly studied by Prof. Henry. A controversy
"A to their cause has attracted more than usual
attention among scientific men because of the
attitude Prof Tyndall has assumed in it,
somewhat ignoring lut otlFiN'S anu Bii'i Viz
coveries of Prof. Henry. Hence the scientific
interest of the new light which has been shed
on the matter by the recent labors of Prof.
Henry but the practical value may prove
equally great.
OF course if the navigator in q fog hears the
distant signal apparently fromHll parts of the
horizon, it affords him no clew to the where
abouts of the source of sound. Apparatus
which Prof Henry has invented may serve to
intensity the sound, but the difficulty as to
direction yet remains. AZ present there seems
to be no pathway out of this difficulty. But II
such analysis could be applied to sound
as the polariscope furnishes for light the
reflected sounds all around the horizon
might be distinguished from that which
comes direct from the fog signal. If no mir
ror he used with the signal to give direction
TO the sound, there would be no other reflected
und than the ocean echoes. If these could
be distinguished, or even extinguished, by an
instrument which gathered the direct sound,
the problem would he solved Considering the
discoveries of cOgnate character which have
been made By Prof. Mayer of Hoboken, the
solution does not seem beyond the range OF
scientific probability.