Evening star. [volume] (Washington, D.C.) 1854-1972, 1893-10-25
SILENT FOG SIGNALS.

A CuriOus Phenomenon Now Being In
vestixated by the Lighthouse Hoard
There is a phenomenon, hitherto unex-
planned, which the government lighthouse
board Is most anxious to elucidate. 1t re-
lates to the sound-carrying power Of fog
signals, the efficacy OF which Is obviously of
the utmost importance for the preservation
Of lives and ships along the coast.
The most powerful kind Of fog signal Is
the steam siren. which has metal trumpet
for a mouth and a boiler like that of a loco
motive for lungs, the place Of vocal chords
being supplied by a revolving toothed wheel,
which interrupts the passage of a jet OF
steam through the throat of the apparatus.
thus producing a frightful 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 dis
lance it is sometimes unheard only three or
four miles away. At the same moment Of
time it may be heard distinctly at ten miles.
inaudibie again at fifteen miles, and once
more audible at twenty-five miles. The phe-
nomenon has been familiar to observers for
many years. Prof. Henry. during his lire
time, tried to investigate it and reached the
conclusion that 1t was due to refraction OF
sound waves caused by the wind. One odd
thing about 1t Is that the believing Of the
instrument can occasionally be heard from
the masthead of a vessel at the same time
that 1t is wholly inaudible from the deck.
Prof. Henry's theory Vas not correct. II
1t were right. the phenomenon would vary
with the Winds Sometimes the sound would
be audible at a given distance from the fog
| signal. and at other times not. according as
the breezes happened to blow. But such Is
not the case. The areas Of audibility and
inaudibility remain the same constantly.
The puzzle Is no nearer to solution now than
| when 1t first excited attention.
Mr.. !. B. johnson, secretary Of the light
| house board, has already devoted good
deal of study to this subject. He Is deter
mined to get at the bottom Of It, With that
end in view he has left Washington In COM
pany with Prof. H. A. 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 ascensions
| within the range Of the fog signal In that
/ locality.
Thus far the belts of audibility and in
audibility for such signals have only been
| explored and mapped out hortzontally-that
| is to say, on the surface of the water Prof.
| Hazen and Mr.. Johnson propose to survey
them vertically. The height Of the"cone" OF
sound. as well as its length and breadth. hav-
| ing in this wise been determined. it will be
possible to make section diagram OF 1t. OF
several. Thus a step will be taken toward
discovering the philosophy Of the phenome'
non.
| The importance or this matter Is reaQny
understood. In time Of fog the mariner de-
ponds on the fog signal as he does on a
| lighthouse in clear weather. If he happens
to get into a belt of inaudibility near to a
dangerous coast, he is lulled into falst
sense Of security,o or, depending on the sirer
for his bearings he does not know where HI
is. Under such conditions the usefulness Of
the signal Is most fatally impaired.
The balloon to be used by Prof. Hazen ant
Mr.. johnson In the experiments referred t
Is the same that was employed by Prof
Hazen and Mr.. Ellis to make an ascension
from Fort Myer in October of last year.
was inflated then with hydrogen. holdin,
5000 cubic feet of the gas. Its lifting capaci
ty was sufficient to elevate the two observ
ers and sixty pounds of ballast. They de
sired to ascertain the conditions OF tn
atmosphere. preliminary to some rain max
ing trials A level Of 400 feet above the eartl
was attained. Probably no balloon of 81
small a size ever made so high a voyag
with such a load.
Prof. Hazen says: II am perfectly salts
fled that the balloon Is to be the salvation
of meteorology In the near future. 1t vii
emancipate us from the thraldom OF theor.
and speculation which has been SO seriou
a drawback DIN the past" . -