Essex County herald. [volume] (Guildhall, Vt.) 1873-1964, 1915-02-12

be said of the harbors of Germany.
But these contrvances for harbor defense, while
much more formidable and dangerous to an enemy,
are harmless to friendly ships. They are what
are known as 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-fire guns shore.
At night they are under constant watch, as we'll
by day, being swept by huge searchghts.
Such mines are hollow spheres of galvanized
iron three feet in diameter, each containing 500
pounds of guncotton, which is lighter than water,
so that they can float They anchored few
feet below the surface in series of lines across
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 checker
board of imaginary squares. This checkerboard is
reproduced on small scale on table In I'M
derground casemate on shore, which Is part of
fort. Suppose hostile vessel to approach. Two
telescopes are aimed at her from points on shore
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 on the table, Moving with the
telescopes the ends of the pointers meet on the
square corresponding to the one where lover the
mine field) 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 used in the business Of planting these
mines and the work being of such great import
ance tile men who undertake 1t highly trained.
Theirs is a branch of the coast artillery which
does it's fighting literally under water and apart
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 over the surveyed having been
ascertaned, wire ropes are measured off into cor.
responding lengths heavy leaden snker Tor
anchor) being attached to one end Of each, and a
mine to the other end. BY this simple means the
sphere Of galvanized iron Is made to float just
many feet below the surface as may be desired
Recently, however, ingenious automatic an
Choir has been contrived, by which, 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
not long ago, miniature ship Of war was scat
tered in smithereeHs at Fort Totem N Y, by
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
battleship within radius of 60 feet, II 1t did not
sink her In a"fed" 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 a main cleo
trio cable, to which each mine is Joined by a
branch cable that meets 1t Just above the anchor.
Thus every mine in 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 are mounted the
telescopes already mentioned for watching hostile
ships.
Sometimes, for the protection of harbors, what
are called "electro-contact" mines are used. They
are much smaller in size, and are commonly ar
ranged in groups Of five or six, which are con-