The Sun.
London, England, 1860-12-13 00:00:00

P ORTS.MOUTLI DEFE S CBS.

The new Hillsea lines for the defence of Ports-
mouth, its harbour, dockyard, and arsenals, from the
attack of an enemy landward, have made consider-

able progress (luring the past summer, and the com-
pletion of the inner or main line is now being
pushed forward with great vigour, 1,500 men being
at this time employed in their construction, 500 in
laying material, and 1,000 in preparing it. The
huge piles of brickwork which form the casemated
batteries for the central bastion have been standing
now nearly 12 months, and not a crack or flaw of
any kind can be discovered in any part of them,
notwithstanding the extraordinary amount of rain
which has fallen during the past six months, and
the swampy nature of the ground on which they
have been built. The lines extend from the shore of
the harbour of Langston, at their eastern, to that of
Portsmouth harbour, at their western extremity,
the earthen line of parapet and ditch being conti-
nued well along the shores of each harbour, the
more effectually to cover the flanks of the works.
This inner line of the defences consists of two im-
mense bastions, with 10-gun casemated batteries on
leach flank, and connected by curtains with demi-
bastions at each end with casemated batteries. The
bastion trace thus presents three fronts, with exte-
rior sides of nearly 800 yards in extent. Each case-
mated flank forms an obtuse angle, with the apex
inclining inwards. The interior of the casemates is
most massive, and would seem destined to bid defi-
ance to any artillery that may at any future time be
brought against them. In the rear of each gun are
quarters for the requisite number of artillerymen to
work it. These arc the only batteries or quarters
for troops which have been constructed along the
main line of defence; consequently, while a heavy
cross fire may be kept up over the defences and
ground in front of the position, not a single gun is
seen pointing directly to the front, nor is an embra-
sure open to an enemy. The faces of the bastions are,

like the curtains, of earth, with a base of 116 feet, a
command of 30 feet, and in every part exposed to
artillery fire,presenting 26 feet depth of parapet. The
summit of the whole line is well traversed with a
parapet for rifle fire, and with the terrepleins, hav-
ing a slope of two feet to the rear. Along the rear
of this line runs a military road from east to west
for the conveyance of materiel, &c., to the different
batteries, while alongside this road is being con-
structed a large drain, which will intercept the
natural drainage of the' land from the base of the
works, and also receive the sewage from the new
barracks now being constructed for the mounted
batteries of Artillery. The remainder of the de-
fences of the Hillsea lines have not yet made much
progress, but preparations are being made to push
them forward as rapidly as possible in the spring.
These will consist of a ditch in front of the inner
line we have already described, 150 feet wide, closed
at each end by machinery when required, at high
water, so as to enable the holders of the works to
alwa3 s retain a certain depth of water in front of
their inner lines of defence. In advance of this ditch
will be constructed two hornworks.of an equilateral
triangular shape, of enormous size and strength,
armed with casemates a la Haxo, in a similar man-
ner to the main line, with which it will be connected
by covert ways, drawbridges, &e., and affording a
safe means of egress and ingress in the event of
sorties, &c., being required. Through the western
work will pass the turnpike road, while through
the eastern one the lines of the South Western and.
South Coast Railways enter and make their exit.
In front of these two works will run the channel
connecting tha harbours of Portsmouth and Lang-
ston, and which will be widened from its present
' extent, 60 feet, to 200 feet, and also deepened suffi-
ciently to allow of first class gun vessels to pass
along in front of the defences from one harbour to
the other—an important consideration in the event
of an enemy advancing to attack the position. The
position along its entire extent will be defilated
from any artillery which can be planted against
it on Portsdown or elsewhere, to the distance of
about 150 yards in the rear of the inner lines. The
lines as they will thus stand, when complete,
might be fairly termed impregnable, Pltwith-
standing the proximity of Portsdown ; but a very
important element of its strength lies in the
nature of the ground in front, as affording the only
way by which an enemy could advance. For 600
yards on the opposite side of the channel to that
on which the works of defence are situated the
ground has a gradual descent along its whole ex-
tent, right and left, so that by simply cutting the
sea walls at high water the whole of this would
become inundated, and form an impassable barrier
to an enemy. Beyond this 600 yards Portsdown
begins its ascent, and continues until it attains its
greatest altitude above high water, 444 feet above
high water mark, at a distance of 2,300 yards from
the Hillsea lines. These heights have been made,
many engineers say, far too much of, considering
the strength of the works at Hillsea, and the com-
position of Portsdown itself, the latter being
nothing but chalk, and therefore quite incapable of
being turned into a Torres Vedras affair. £650,000
has been named by the Defence Commission as the
sum required to fortify these heights, which are
seven miles in extent, and for the purpose of carry-
ing this out, Colonel Ross, R.E., and staff are

already in possession, and have marked out the
sites for the various forts, which are recommended
to consist of four forts of 30 guns each, two of 25

guns each, and three of 12 guns each, with flanking
lines of escarpment at Farlington and Fareham.
The ground, however, is not yet broken. The ap-
proach to Portsdown-hill will be sufficiently
guarded at its western extremity by the chain cf
connected forts extending from Stoke's Bay to
Frater Lake, and by the advanced line of detached
works from Hill-head, opposite Osborne-house, to
Old Ford, near Fareham. The approach to its
eastern extremity will be, however, entirely
unpro-
tected; while, strange to say, this is the only point
from which an enemy, landing on any part of our
coasts in the English Channel, can be expected to
make his appearance. Seises. Bill, some few miles
from Chichester, is the only spot in the Channel
which would afford an enemy smooth water to land
in a south-west wind, and without a single gun to
opposite their landing. Ihe landing once effected
Selsea Bill could be fortified sufficiently with a
couple of batteries, and a base of operations Would
be at once secured.