The Express.
London, England, 1863-08-25 00:00:00

THE PORTS AT SPITHEAD.

Orders have been igented for the fortifications of
ilpithand to be proceeded with at owe, and by the early
part of the ensuing sprusg the work of laying down the
foundations will have begun in real earnest. There are to
be throe forts, stationed respectively on the Horse, Noreen,
and Sturbridge shoals. The Hone shoal stretches for a
coesiderable dretaises into the sea from the mutilate shore
of Forfar Island, and it forms the north-east boundary of
I the only channel which makes Portsmouth harbour tamest.
hie to large vessels. The south-west boundary of this
' channel is termed by the Noonan shoal, which juts out
from the north-mut shore of the Isle of Wight;
and it is upon the extreme points of these
' shoals, that is to say, when the channel is the
narrowest, that two of the forts are to to constructed, the
breadth of navigade water between them being about 2,100
feet. The Sturbridge shoal lies man sway to the west-
! ward, off Hyde, and the fort to be raised there will not
only prove to be exceedingly dangerous to any vessel at-
tempting to run between it and the lile of Wight, but will
cram sre with a powerful independent buttery flanking
Fort Megaton, at the eastern point of Stokes Bay. The
distance between the Sturbridge and the Norman shoals is
4.000 yards, and between the Sturbridge and the Horse
5,330. A narrow channel runs between the Hunan and
the Isle of Wight, but it is awe to the site of the pro-
p:god battery, and if it ran I. shore it would be ex-
posed. to • powerful battery which is being erected es the
liaised at Pnekpool, only 3.300 yards away from the Noma.
With regard to the superstructure of the insulated forte, it
is impassible to give any deeeriptioo at present, for the oir
viously satisfactory reason that no plans have as yet been
prepared. It will be two year at least before the heeds-
tithe are laid, and science may in the meantime do meek
towards perfecting our knowledge of the art of defence.
The pram:oat intention is to build the superstructure of iron,
and the strength of the basement will, therefore, be proper-
booed to the weight which it is intended to bear. All the
forts will be circular in form, the external diameter ben
205 feet, and the foundation will be faced with
granite. As to the number of guns with which each is to
be armed, that of course depends upon the progress which
is made in artillery science, but there can be so doubt that
they will be armed with guns of the busiest calibre which
it is possible to make. In laying the foundations of works
of this had, of course the great object is to obtain a good
bottom. So fee as the Horse shoal is concerned—and it II
the only one where any preoise examination has been com-
pleted—nature has strongly favoured us in this respect. It
is there found that an artificial bottom will be perfectly un-
necessary. The depth over the shoed is shout 11 feet
at low water spring tide. The boring of the shoal
to the depth of S 5 feet shows that the upper
stratum monists of 5 feet of compact shingle sod
sand ; the sewed stratum is oompteed of 18 feet of sand,
containing pieces of bark and breeches of trees, pertly car-
booised ; the third, of blue clay, containing layers of vege-
table matter, eight feet thick ; the fourth, shingle and sand
with shells, five feet thick ; the fifth, blue silty clay, to the
depth of 17 feet, and then sand and shingle. The shoal is,
therefore, substantial enough to bear any weight, and the
boring as been carried so far, not for the purpose of find-
ing • more substantial foundation, but to obtain fresh miter.
The method by which this mutt is tobe obtained ts ingenious
yet simple. A wrought iron cylinder, six feet in diameter, is
sunk into the upper stratum, and as the various strata axe
excavated by divers inside sod the cylinder sinks lower and
lower, successive lengths of cast iron tube, of the same
diameter, are added to it As we have already intimated,
this cylinder has beep sank to the depth of 55 feet below
the surface of the shoal, and 90 feet below high water mark,
and the divers now experience considerable difficulty in pur-
suing their labours, inure:tab as the pressure of atmosphere
pumped into the helmet is nearly three times the pressure
of the atmosphere on the surface of the earth. Sir Horton '
Peto Ilse fallen into a strange error in forming an
opinion as to the use of this cylinder. In a pamphlet
which be has recently published, he gravely informs
the public that a theft bas been sunk to the depth
of 50 or 60 feet, nod that go bottom use as yet been found
of sufficient stability for the construction of • fort, the fact
being that the upper stratum is sufficiently compact for the
purpose, without any artificial fouodation whatever, and the
simple use of the shaft is, as we have already described, to
obtain a supply of fresh water. The Sturbridge shoal dif.
fen from the Horse in the fact that it consists of a bank of
clay, and will probably rer,uire an artificial foundation, the
depth of water over it at low spring tides being abort 17 feet.
The Homan, it is expected, willofter a foundation equally sub-
stantial with that at the Horse. For the cunt uctiou of
these works, a circular staging will be erected roiled each
fort, sad epos it will be constructed radiating steam travel-
lers, so that the does and other material will be raised from
the Teasels by steam power, and deposited on the exact spot
where it is required. The pikes upon which the superetroc
tare of the staging will be supported will be fitted with
heavy cast iron screws, and will be strewed into the ground
by means of a capstan bud fixed upon each pile. The
fonadotioes will not be laid by means d a coffer dam.
as in ordinary eases, but the ground will be levelled
and each block of stops laid by divers in helmets. The con-
struction of thews extensive works will be under the super-
intendenee of Mr. Hawkehaw, of Great Gr nip-street,
London ' • the resident engineer being Mr. Harris, son of
Sir William Snow Kerrie. The contractor is Mr. Leather,
who was also the contractor for the construction of Port-
laud Breakwater. Hr. Leather has already begun the
establishment of extensive works in Stokes Bay for the
manufacture of concrete blacks and the preparation sod re-
tuition of stone and other material used in the foundation
of the fort., and to facilitate shipment he has constructed a
pier with • steam crane. —Hampshire Tefeyreph.