The sun., 1898-06-26

has aports to be defended, there j
naturally variety of submarine mines
and only the officers in the torpedo ser
vice OF each country know just what con
triyances are prepared for keeping hos
tile fleets out of its harbors or blowing
holes into them when they do get in.
But broadly speaking, all harbors ARK
defended by observation mines" OF
contact Mines and operations in mine
destroying will be directed against these
two kinds OF mines.
Observation mines are mines connected
with the shore by electricity cables by
means OF which an operator stationed at
a polnt-usually a protected and masked
pit-whence the movements of attacking
ships may be observed, can turn key
and explode series of mines at the
moment a vessel passes over them.
These mines are placed III rows across
a channel. Each mile is spherical or
cylindrical copper case containing about
800 pounds of gnncotton. 1t is about
three feet in diameter. The explosion
of this quantity of guncotton will be fatal
to any ship within radius of sixty feet
from the point on the surface above it. A
line of six mines will, therefore, guard a
channel 720 feet wide
Guncottoa is lighter than water, so an
observation mine is attached to an iron
sinker weighing about a quarter of ton.
Each row of mines is strung on one elec-
trio cable, which is attached to the
sinkers and runs along the bottom.
The wire mooring rope, by which each
mine is attached to its sinker, is between
ten and fifteen feet long, so that the mines
float at this distance from the bottom. II
the mines are nearer than this to the
bottom, the explosion of the first one is
liable to break the cable and cut off the
electric current from the other mines be-
fore they explode.
Each mine is joined to the main ell, c.
trio table by branch cable meeting it at
the point where it is cornec ed to the
sinker. For the guidance of the operator,
buoys are placed at the ends of each line
of mines.
At night Holme lights or something
similar are used. These lights are an
inge Aious invention and are used when
ever it is necessary to make temporary
marks in the water at night. They con-
sist of chemical composition that in
contact with water generates gas which
ignites and burns with a dull light when
it reaches the air. The light is placed
below the surface and the rising bubbles
mark its position. Mined harbors are
filled with false buoys and lights to de-
ceive the enemy.
Observation mines of the ordinary
kind should be from 40 to 60 feet below
! tho S,,rfnna A fhic roipt tbn,, ,rn Ga, e.,
as may be from attack, and they exert
the greatest force against the bottom OF a
ship.
Two kinds of contact mines are in
general use, the electro-contact and the
mechanical or automatic. They are in
tended to explode only when they are
struck by bottom of ship. The pro-
per depth of these mines is fifteen feet
They are about one-tifth the size of an
observation mine, are moored to sinkers,
and the electro-contact mine is joined by
an electric cable to a battery at the firing
station on shore.
A number of these mines, arranged in
groups OF from three to half dozen, are
usually connected with one main cable.
Where the branch cables meet the main
one there is \ hat is called disconnector
box that protects the connections.
Electro-contact mines are quite harmless
until the electricity is turned on; they
are ready to explode when ship hits
them and completes the circuit by acting
upon the circuit closer.
This delicate little machine is re-
markable feature in these mines There
are many different styles of circuit clos
ers, upon which boundless ingenuity has
been expended. One kind consists of a
metal cup filled with mercury to IA point
just below metal bar that enters the
cup without touching it or the mercury.
When the mine is floating upright the
mercury is level and the space bet ween
it and the bar breaks the circuit Ii the
mine is tipped to an angle of about 70
degrees, as will happen when ships
bottom pushes against il, the mercury
reaches the metal bar, the circuit is
closed and there is an explosion.
There are varieties of automatic mines.
One in general use is like the electric
contact mine, except that it's battery
is part OF its internal organs, and it has
no connection with the shore. Some me-
chanical mines are exploded by pressure
Il blow equal to five pounds being
enough. To make these conclusion
mines more stable they sometimes are
fastened to their sinkers by poles instead
of mOoring ropes.
When hostile fleet is expected the
regular mine defense is in most cases
supplemented by extemporzed mines of
gunpowdcr and dynamite.
There are three recognized meth DIS of
mine destroying. Two ot these are ef-
fective against all varieties of submarine
explosives; the third, ''grappling,' can
not be used in destroying automatic
mines that are not fired from the shore |
by means of wires
The process called "Swecping' chan
mel can be employed only after the
enemy's guns are slenced or in clearing
outlying mine fields that are not reached |
by bullets. A sweep consists Of two
parallel ropes, say 80 feet long, con-
nected at the middle and both ends by
cross ropes long enough to reach to the
bottom of the channel. The top rope
has buoys fastened ut the ends and the
middle, which hold it at rhe surface
while the second line drags along the
bottom, being weighted at the middle by
Il heavy shot.
At either end of the bottom rope of the