The Raymer enterprise., 1915-02-04

be said Of the harbors OF Germany
But these contriyances for harbor defense, while
much more formidable and dangerous TO 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 of by the
sending OF an electric spark at moment when a
hostile vessel may happen to be within range Of
their tremendous explosive activities
All the nayigable channels of the harbor Of
Portsmouth, for example. are at this moment
guarded by an elaborate system of mine fields"
which are protected by rapidfre guns on shore
At night they under constant watch, as well
as by day, being swept by huge searchights
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 are anchored few
feet below the surface In a series of lines across
a channel, about eighty feet apart in each line.
II an enemy's ship were to succeed by good luck
In getting through one line without being blown
up. she could hardly pass another
The area OF water surface covered by mine
field is laid of tby careful survey in checker
board OF imaginary squares This eheckerboard is
reproduced on small scale on table In an un.
derground casemate on 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 on the table. Moving with the
telescopes. the ends OF the pointers meet on the
square corresponding to the one where lover the
mine feld) the vessel actually is A 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 II are highly trained
Theirs is branch OF the coast artillery which
does its 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 explosive,
part OF the preliminary work of establishing
mine field consists In making soundings. The
depths all over the surveyed area having been
ascertained, wire ropes are measured of into cor.
responding lengths. heavy leaden sinker Tor
anchorl being attached to one end OF each, and a
mine 10 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 an ingenious automatic an
chor" has been oontrived by which no matte.
what the depth. exactly the required submergences
for each submarine may be obtained ofhand
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 huks. and on this side of the water
not long ago. miniature ship of war was scat.
tered in smithereens at Fort Totten. N. Y, by
mine Of corresponding size ignlted 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 gnneotton would at least disable the stoutes
battleship within radius of 60 feet If II 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 Tor anchors) and runs along the bottom
The rows are connected together by main cleo
trio cable, to which each mine is Joined by
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. II 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 "electrocontaet' mines are used They
are much smaller In. size, and are commonly ar
To-, 80 G,TA ufv rkt