The Portland daily press., 1896-03-21

tanee IN one direction, while in another
it will be scarcely audible at the distance
of mile. This is not the effect of wind,
as the signal is frequently heard much
farther against the wind than with it;
for example, the whistle on Cape Eliza
beth can always be distinctly heard in
Portland' distance of nine miles, dur
ing neavy northeast snow storm, the
Wlnd blowing gale directly from Port.
land toward the whistle.
Inc most perplexing difficulty, how
ever, arises fIom the fact that the signal
oIten appears to he surrounded by belt.
varying in radius from one to one and
one-half miles, from which the sound an
pears to be entirely absent. Thus, in
moving dirently from station, the sound
ls audible for the distance of mile, is
ghen LOST for about the same distance. af
Ter which 1t is again distinctly heard for
long time. This action Is common to
all ear-slgnals, and has been at times OBJ
served at Ill the stations; at one of which
the signal is situated on bare rock
twenty miles from the main land, with
no surrounding objects to affect the
sound.
Steamers are constantly running
among the islands on the coast of Maine
during the summer. This is the season
OF tnlck and persistent fog. When pilots
can nardly see the length of their vessel,
shey Keep up constant noise with their
log signals. The open sea gives back no
sounu. But the near or remote vicinity
OF cilffs, bluffs, or even high shores, is
Indicated by the strength of the echo re-
celved back from them. In fact, running
by echo is recognized as one of the neces-
sltleS OF the navigation of these waters.
This method is also used to soma ex-
tent by steamers on the great rivers, and
Is practlced on the great lakes to some
extent, notably at certain bluff jutting
out into Lake Superior.
II the law of these alterations in au-
d1p1iity can be evolved and some method
discovered for their correction, as the
variations of the compass are corrected,
tnen sound may be depended upon as
more definite and accurate aid to nayi-
gatlon. Until then the mariner will do
well when he does not get the expected
sound OF fog signal, to assume that he
may not hear warming that is faithful
~ given, and then to heave his lead, and
resort TO the other means used by the
careful navigator to make sure Of his
position.
A fog-signaling device now under con-
slderatlon by the light house board is the
invention of MIR. De la Tore of Balti-
more. 1t is what may be called an echo
maker, and consists of faring funnel
scr eWed on the muzzle of rifle. 1t is
operated by firing the rifle in the direc-
tlon OF the supposed obstacle, such as a
rock, an iceberg, another ship, or a cliff.
Ii the obstacle is there the beam of sound
projected through the funnel strikes the
obstacle and rebounds; and as the echo is
more or less perfect in proportion as the
obstacle is more or less parallel to the
ship from which the gun is fred, and it
Is near or remote, the position Of the OBJ
stacle may thus be inferred. The board
reported that De La Torres method was
firing blank cartridge from a rifle In
the presence of objects as small as a spar
buoy and as large as fort and catching
the return sound or echo.
He claims that sharp sound project
ed at or nearly at an object, and only
when SO directed, will in every case re-
turn some of the sound sent so that theo-
retically there will always be an echo,
and the difference in the time between
the sound sent and the echo will indi-
cate the remoteness of the object. The
board found that a return sound could be
heard from the side of a fort half mile
off, from passing steamers a quarter
mile off if broadside to. from bluffs and
sails of vessels about the same distance,
and from spar-buoys 200 yards away.
"The board further states that the
sound from the different kinds o f masses
Is different in most cases, and that the
ear could be educated to detect quite q
range of different objects, as the echo
from a sail was different from the echo
from a buoy or bluff. If two objects
were near the line Of projection at differ
emit distances an echo would be received
from each. The horizontal limit of the
return of sound seemed to be about two
points on each side of the axis of projec-
tion.
"If Mr.. De La Tore should see fit to
construct his instrument for hearing
feeble echoes the board indicated that it
would recommend that it be fitted soon
to some vessel of the North Atlantic sta
ton. and that further and, if possible, ex-
haustive experiments ought to be made
to practically determine the use of the
echo as a means to discover obstacles to
navigation. It was also stated that steam
whistles could be heard much farther
than the echo; but it was said that where
the obstacle could not make the sound,
as in the case of an iceberg, the echo
would be of the greatest use, and expert
ments looking to it's utilization are de-
manded by the conditions of navigation
in time Of fog"