The Portland daily press., 1893-10-30
SILENT FOG SIGNALS.
A Curious Phenomenon Now Being In
vestigated by the Lighthouse Board.

There is phenomenon hitherto unex-
planned, which the government light
house board is most anxious to elucidate.
1t relates to the sound-carrying power of
fog signals, the efficacys.of which is OBJ
viously of the utmost Importance for the
preservation Of lives and ships along the
coats. The most powerful kind of sig
nal is the steam siren which has metal
trumpet for mouth and boiler like a
locomotive for lungs, 1.-THE place of vocal
chords being supplied by revolving
toothed wheel, which interrupts the pas
sage of a jet of steam through the throat
OF the.apparatus, this producing the fright
full shrek that rises from note to note of
the scale as the wheel goes faster.
1t is the most penetrating sound known
and can be heard in calm weather at a
distance of forty miles. Nevertheless
while audible at that distance, it is
sometimes inaudible only three OF four
miles away. AT the same moment of
time it may be heard distinctly at ten
miles, inaudible again at fifteen miles,
and once more audible at Twenty-Five
miles. The phenomenon has been familiar
W OUScIFcIS lOI Iudny IOl.
Henry, during his lifetime tried to inves-
tigate it and reached the conclusion that
it was due to q. refraction of sound waves
caused by the wind. One odd thing
about it is that the believing of the in
strument can occasionally be heard from
the masthead of vessel at ethe same
time that it is wholly inaudible from
the deck
Prof. Henry's theory was not correct.
1t it were right, the phenomenon would
vary with the winds. Sometimes the
sound would be audible at a given dis
lance from the fog signal, and at other
times not, according as the breezes hap
pened to blow. But such is not the
case. The areas of audibility and inaudi-
bility remain the same constantly. The
puzzle is no nearer to solution now than
when it first excited attention.
Mr. B. F. johnson. secretary of the
lighthouse board, has already devoted
a good deal of study two this subject.
He is determined to get at the bottom
Of it. With that end in view he has
left Washington in company with Prof.
Hazen of the weather bureau their
destination being Little Gull Island, off
the coast of Rhode Island. They have
taken with them a balloon, in which
they propose to make a series of ascen-
sions within the range of the fog signal
in that locality.
Thus far the belts of audibiIity and
inaudibility for such signals have only
tally-that is to say on the surface of
the water. Prof. Hazen and Mr.. John
son propose to survey them vertically.
The height of the "cone" of sound,
as well as its length and breadth, having
in this wise been determined, it will
| be possible to make a section diagram
of it, or several. Thus step will
be taken toward discovering the phil
osophy of the phenomenon.
The Importance of this matter is
| readily understood. In time Of fog the
mariner depends on the fog signal as he
does on lighthouse in clear weather.
| Ii he happens to get into belt of
| inaudibility near to a dangerous coast,
| he is lulled into false sense of securl-
| ty, or, depending on the siren for his
bearings, he does not know where he is
| Under such conditions the usefulness
of the signal is most fatally impaired.
| The balloon to be used by Prof. Hazen
| and Mr.. johnson in the experiments re-
| ferred to is the same that was employed
| by Prof. Hazen. 1t was inflated
with hydrogen, holding 5000 cubic feet
of the gas. It's lifting capacity was
| sufficient to elevate the two observers and
sixty pounds of ballast. They desired
| to ascertain the condition of the atmo-
| sphere, preliminary to some rain making
| trials A level of 9,40O feet above the
earth was attained. Probably no balloon
| of so small size ever made so high a
voyage with such a load.
| Prof. Hazen says: II am perfectly
satisfied that the balloon is to be the
future 1t will emancipate us from the
thraldom of theory and speculation
which has been SO serious a draw back in
| the pastn