Evening star. [volume] (Washington, D.C.) 1854-1972, 1926-08-29

While there remains some un-
certainty as to just how many enemy
submarines We're actually located by
underwater listening machines during
the World War, the development of
these instruments in the anti-sub-
marine campaigns has certainly re-
suited in a much improved sonic
depth finding device which has been
used since the war. Whole sections of
the ocean bed have been charted,
cables have been laid, and icebergs
have been traced through the instru-
mentality of the devices which the
war helped develop. Thus, the stimu-
lus given to invention by the terrors
Of the U-boats has had lasting bene-
fit. The United States Navy Depart
ment makes no secret of the success
it has achieved in developing under
water listening for peace-time uses.
Whether 1t has also perfected a per-
feet submarine detector is not known.
Presumably the progress in peaceful
invention has it's parallel in perfecting
defensive equipment for war.
The sonic depth-finder, as developed
since the war by the Navy, bids fair
to displace completely the old system
of sOundings by weight and line. A
vessel equipped with the new inven-
tons can determine the depth of
water under it as it goes along. With
out slackening speed, and while for
some time this process worked eftec-
lively only at depths in excess of y
fathomS. it is now useful at depths
of that many feet. Some $4,000 square
miles of the bottom of the Pacific
Ocean between San Francisco and
San Diego have been charted by two
destroyers, steaming at the rate OF
~ knots an hour. while they made
soundings by sound waves. This work
would have required several years II
carried out by the weight and line
method Of measuring depths.
Fixed Rate of Sound Travel.
The sonic depth-finder and similar
devices for locating icebergs or SUBJ
marines are founded on the knowl-
edge that sound travels through sea
water at a fixed rate, and that by
timing sound wave from one point
to another the distance can be de-
termined. Thus q sound started from
a ship goes to the ocean bottom anu
echoes back to the ship. BY meas
uring the time elapsed, the depth OF
water under the ship is determined.
In the same way a SOund-WaVe echO
from an iceberg serves to locate the
berg.
With submarine or other sounds
coming directly from objects distant
from the receiving point, there Is
basis for judging direction, but not
for measuring distance, as the time
of the sound waves travel Is I'M
known. If. however, after locating a
submarine, for example, an echo can
be got from it. the time can be meas
tired and the distance calculated
This principle Of timing sound
waves is simple but the machinery to
make 1t effective is not, and it took
wears of work to complete the discov-
cries and devices necessary to make it
practical. AS early as 1908 expert
ments were made from lightships by
using submarine bells to transmit
sounds and microphones in tanks
against a ships side to receive them.
These experiments worked fairly Well
for a few miles. In 1914 DIR. K. A.
Fessenden perfected the Fessenden
oscillator. which sends out high
pitched sound waves from the steel
hull of a vessel by electric vibrations.
These waves proved far more effec-
tive than those from bells, and from
them the first echoes were noted, indl-
eating that the sound waves went to
the bottom and We're sent bounding
back.
Testing Speed of Sound.
Meanwhile, in 1911, Navy expert
ments with the cruiser Washington
off the Nantucket Shoals Lightship
had determined the rate at which
sound waves travel through sea water.
This was done by releasing radio sig
nails and submarine bell signals at the
same instant from the iightship and
noting the time of arrival of each on
the Washington's receiving devices.
The cruiser made a series of tests at
an exactly known distance from the
lightship. until the rate of transmits
sion of the sound waves was deter
mined, and then steamed to sea and
made other tests at various distances.
From this series or experiments the
rate of sound travel through sea water
was determined as being 4,S00 feet
per second, a fact which formed a
basis for a vast amount of subse-
quent experimentation.
When the World War began, the
Navy had some knowledge of under
water sound detection, but no method
of determining the direction from
which sound waves came. The war
experiments produced a submarine
sound receiver capable Of doing just
that thing. namely, Of determining the
bearings of the source of a submarine
sound. 1t was this discovery which,
after the war, was first applied for
the taking of depth soundings. These
were taken by getting the record of
the echo from the propeller of ship
recorded on a receiving device at the
bow of the vessel. The angle at which
the echo came from the sea bottom
taken together with the length of the