The Winslow mail., 1915-02-27


be said of the harbors of Germany.
But these contrivances for harbor defense, while
much formidable and dangerous to an enemy,
are harmless to friendly ships. They are what
are known observation mines," and, being con-
nected by wire with the shore, are set off by the
sending of an electric spark at moment when
hostile vessel may happen to be within range Of
their tremendous explosive activities
All the navigable channels of the harbor of
Portsmouth, for example, are at this moment
guarded by an elaborate system of mine fields"
which are protected by rapid-fre guns on shore
At night they are under constant watch, as well
as by day. being swept by huge searchlights.
Such mines are hollow spheres of galvanized
iron three feet in diameter, each containing 500
pounds Of gupcotton, which is lighter than Nater
so thet they can float They are anchored few
feet below the surface in series of lines across
O channel, about eighty feet apart in each line.
If an enemy's ship were to succeed by good luck
in getting through line without being blown
up she could hardly pass another.
The area of water surface covered by mine
field Is laid off (by careful survey in a checker,
board Of imaginary squares. This checkerboard is
reproduced on a small scale on table In an un-
derground casemate shore, which is part of
fort. Suppose hostile vessel to approach Two
telescopes are aimed at her from points on shore
some hundreds of yards apart their lines of sight
crossing of course, at the spot where she floats
The telescopes are electrically connected with two
pointers that move the table Moving with the
telescopes, the ends of the pointers meet the
square corresponding to the one where (over the
mine feld) the vessel actually is. button mark.
ed with the number of that square is touched and
bang!-she is blown sky-high
Small steamers especially equipped for the pur
pose are used In the business of planting these
mines and the work being of such great import
ance, the men who undertake 1t are highly trained
Theirs is branch of the coast artillery which
Sf
from the mechanical details OF their employment,
they must have fairly expert acquaintance with
electricity and the chemistry Of explosives.
part Of the preliminary work of establishing
"a mine field consists in making soundings. The
depths all the surveyed area having been
ascertaned, wire ropes measured off into cor
responding lengths heavy leaden sinker Tor
anchor) being attached to one end of each, and
mine to the other end BY this simple means the
sphere Of galvanized iron is made to float just as
many feet below the surface as may be desired
Recently, however ingenious automatic an
chor" has been contrived by which, no matter
what the Depth exactly the required submergences
for each submarine may be obtained 'offhand.
AS yet experience in actual warfare has not
afforded practical demonstration of the usefulness
of such observation mines. But of their destruc-
tive power there can be no question. Many ex-
periments have been made with them in the blow
ing up of old hulks, and this side of the water,
not long ago, miniature ship of war was scat,
tered in smthereens at Fort Totten, N. Y by a
mine of corresponding size ignited by an electric
spark from distance of mile and quarter.
From such trials the conclusion has been drawn
that the explosion of mine containing 500 pounds
of guncotton would at least disable the stoutest
batteship within a radius of 60 feet If 1t did not
sink her In field" defending harbor channel
each row Of galvanized iron spheres is strung
along one electric cable, which is attached to the
sinkers Cor anchors) and runs along the bottom
The rows are connected together by main cleo
trio cable, to which each mine is joined by a
branch cable that meets it just above the anchor
Thus every mine N the field" is under direct
control by the apparatus in the casemate on shore
The casemate is an underground room, lined
with concrete, and containing all the mechanism
for controlling the mine system. 1t is connected
by telephone and otherwise electrically with the
two observing stations, in which mounted tbs
telescopes already mentioned for watching hostile
ships.
Sometimes, for the protection of harbors, wha
are called "eectro-contact" mines used The!
are much smaller in size. and are commonly ar
ranged in groups of five six which are con