Burlington weekly free press. [volume] (Burlington, Vt.) 1866-1928, 1898-07-14
MINES IN A HARBOR.
TWO KINDS, OBSERVATION AND ELEc-
TRIO CONTACT, ARE USED.
The Way In Which They Are Planted and
Methods by Which They Are Exploded.
Uses OF the Signal and the Firing Elec-
trical Current.

In fortifying hnrbor against attack by
an cncmy's fleet tho British engineers
would use today submarine mines Of two
general classcs-the observation" and
the electro contact" The observation
mine, so called because its action Is direct
ed by an observer or operator stationed on
shore, Is q convex ended cylinder of Stat
fordshire plate thrco-sixtccnths of an
inch in thickness, measuring 81 inches in
depth and about 32 inches in diameter
Within tho cylinder and surrounded by an
air chamber is n core composed of % sep
aratc copper cases, containing In all 500
pounds Of wet gun cotton. Tho central
case of the % Is arranged to receive tho
"primcrtn," n little box holding two Diet
orators, or fuses, Undecided in Cry gun
cotton, from which electric wires pass to
the insulator at tho mouth of the minc.
For harbor defense the engineers would
lay observation mines in groups Of at least
six, placed in n fundamentally straight
line at intervals of $50 feet, and preferably
in about 30 feet of water. Ono main cleo
trio cable, starting from the operate 8
station on shore, would connect with and
govern each mine of the six, reaching it
by IL fork or branch running to its insu-
lator. This main cable would be close to
the harbor bed, but the mines themselves,
whose buoyancy is considerable, would
float i2 feet or more above, each anchored
by stout steel wire nooring rope to
wrought iron sinkcr of 300 pounds weight,
disk shaped, with concavc lower surface
to give tho additional hold of suction. At
about go feet from the outer and inner
ends Of tho mine limo mark buoys would
be set to guide the eye of the shore opcr-
ntor whilc various other buoys would be
scattered around the field in order to mys-
tify tho cnomy.
For Tic operators station the two great
requirements are clear sweep of vision
over the mncilclds and invisiblity. a
littlc cave dug In % hillside or cmbnnk-
mcnt and disguised with bushes, vines or
whatever Is the common foliage of tho
spot Is the ideal arrangement, but If ncccs-
sity forces the selection of fiat and barren
ground n hut may be rendered inconspicu-
Gus by u coat of paint of the color of the
earth about 1t. Here the observer sits his
| glass trained on the two range buoys Of
| his special group of mines and his battery
and firing key within easy reach. AS the
encmy's ship or ships cross his sight limo
he presses the key, and in an almost meal
culably small fraction of u second the
whole group OF mines is exploded. The
fatal area of each individual mino Of the
Conservation" type covers a circle 60 feet
in diameter. Reckoning with the breadth
of beam of the average warship as n factor,
it thence appears that the series of six will
| clear u channel about 720 feet broad of
any vessels unfortunate enough to be there.
Tho electro contact" differs from tho
observation mine in that it is meant to OK
| plodc on actual contact with the ship S
bottom, not at some distance beneath. 1t
is used in deeper water than is the other
variety and Is fitted with much higher
charge, since rs pounds of gun cotton de-
| tOnatcd against the hull of the strongest
vessel built is quite sufficient to disable II
not TO destroy her. This minc like tho
species previously described, is contained
in n convex ended iron cylinder its charge,
rs in the former case, packed in nest of
! copper boxes, tho central box holding the
primer tin with its two dctonators and
their electro wiro connection. One leg
of the wire necessary TO complete the firing
circuit runs, however, not directly to Its
detonator, but to the top of the mine as it
| lies alloat, there entering an ingenious
contriyance called u circuit closer. The
mine cannot explode until the circuit
closer comes into action, and tho circuit
closer will act only when struck by tho
| hull of u ship.
Electro contact mines arc commonly
laid in several connected groups of three.
| Each individual in each trio has its own
electric cable, about 100 yards in length
the three cables converging Mt their lower
ends to enter n "Gisconncctor box" Tho
disconncctor in turn sends down a single
200 yard cable to multiple junction
box, within which it meets similar ca
bles from the disconncctOrs of all tho 9th
er trio5 In the series, and with them Ii
joined to u main cable running to tho bat
terry in tho operators station on shore
| Tho operator has it in his power to put
the whole series instantly out of play ant
to return 1t as instantly to service, and by
means of the disconnectors any trio which
having been exploded, has become an in
cumbranco to the rest may be cut out Of
the circuit.
a ground mine, like the observation
mine, is laid in relatively shallow water
depth of 30 feet by choice-and has IL ca
bic connection with an operators battery
on shore. Attached by cable to tho minC
and floating above it at such point as Il
be likely to be struck by any passing YES
sci Is n buoy containing an electric appa
ratus with n circuit closer. When tn,
operator turns strong electric current in
to tho main cable, the touch of ship,
hull on the buoy is sufficient to detonat,
the mine. This powerful force is put IL
action at night or at any time when The
enemy's ships alone are expected to be IL
the harbor. On all other occasions thu
current Is maintained at vcyy low ebb
when pressure on the buoy would not
fire the mine. but would merely telegraph
u signal to the shore station, indicating Il
the observer there which particular buo,
had been struck. Tho change from sigma
current to firing current may be made II
an instant, so that in the event of harho
engagement between friendly and hostil,
fleets u homo vessel may be allowed t.
pass unscathed over the mine, while tn,
rncmy's ship, touching the buoy immedi
ately afterward, will be wrecked on tn,
spot. The ground mine is not however
dependent for its explosive power on tn,
collision of II ship with the buoy. TIL,
shore operator may explode it at yolitior
whenever, in his opinion, occasion arises
but it Is always difficult to tell csactl,
what point on the range line II crossing
vessel occupies, and for that reason tn,
mines arc laid in groups of three, all three
to be fired simultaneously in case of "judg
ment action"
"The great desdcratum in efficient min
ing" says recent authority, lis not 81
much perfection in construction as abso
lutte secrecy in the plan of laying.
If the plan of the mines position is KEEP
secret, they constitute far more eflicicn
protection to harbor than any amour
Of forts and guns. An opposing
fleet might easily bring itself to attack