Guildford Viaduct, Guildford Road, Guildford, Hayle

VIADUCT BUILDING IN CORNWALL.

(From the Mining Joumal.)

The great mistake of building railway viaducts in Corn-
wall of wood, seeing that it is a land of stone, is now being
rectified at enormous expense by the Great Western Rail-
way Company. Several wooden viaducts have already been
replaced by stone bridges, some of which, especially those
at Moorswater, near Liskeard, and at Angarrack, near
Hayle, are magnificent examples of masonry. The con-
tract for re-building two other viaducts-one at Guildford,
near Hayle, and the other at Redruth-have just been let
to Mr. Stevens, of Ashburton. That at Redruth will be
remembered best by strangers, as from the train it seems
to rise almost out of the roofs of the houses, being
almost hemmed in by buildings ; and in order to avoid
the expense of buying up valuable property, the new
viaduct is to occupy partly the site of the old one. In
order to. accomplish this without interruption of traffic
the new viaduct will be built in sections. Sufficient
to carry the down line will be built first, and when com-
plete the lines of rails will be shifted on to it. The wooden
viaduct will then be taken down, and the permanent struc-
ture widened on the site of the old to the extent of 28 feet
for the two lines of rails. While the railway company will
thus avoid the expense of buying up property they enter
upon an engineering feat of no little difficulty. The new
viaduct is to be about 600 feet long, 28 feet wide, and the
lino of rails 60 feet above the principal street, and is to
consist of seven arches of 57 feet span, and one arch of 51
feet open, and will be constructed entirely of granite. The
engineer is Mr. Gibbons, of Lostwithiel, the monuments of
whose skill bid fair to equal the Roman aquoducts. The
granite is to be supplied by the Cornish Granite and
Freestone Company, from their quarries at Carn
Marth, about one mile from Redruth. The quarries
have been worked for many years, some of the
granite used in the Thames Embankment, and in the
Chatham, Cardiff, and other docks having been brought
from here. One of the first stones raised for this work
was a rock weighing about 200 tons, which had to be lifted
out of its bed in the quarry preparatory to being split up
into requisite sizes. For this purpose two blast holes were
bored, each 16 feet back from the face ; each hole was 10
feet deep, one being 4 1/2 inches and the other 3 1/2 inches in
diameter. Each were charged 4 feet deep with pebble
powder. The object in view was not so much to break the
stone as to lift is, and for that purpose experienced quarry-
men prefer powder to any other explosive. Dynamite,
although more powerful, shatters, while powder lifts. The
holes were five feet apart, so as to distribute the
force. The essential requisite in blasting of this kind
is that they shall be simultaneous, not only from
dynamic considerations, but also in the interests
of safety. The simultaneous blast was in this
instance accomplished by the patent igniter and
instantaneous fuse invented and patented by Messrs.
Bickford-Smith and Co., of Tuckingmill. The quarry
manager, Mr. Hicks, adoptcd this fuse, believing it to be
more safe; certain, and economic than any electric ap-
pliances yet introduced. The invention consists of a small
tin tuboeabout three inches long, into which is let at one
end the usual slow safety-fuse, and at the other end so
many instantaneous fuses as may be required, In this
particular case there were only two heavy charges to be
blasted, but the principle is the same with any number,
more than twenty being sometimes similarly treated. The
fuses wore carried through tamping and powder to within
three inches of the bottom, and gave a perfect success, in-
as much as the huge »tone was shifted sufficiently to enable
the workmen to split it in requisite sizes. The advantage
of this new patent of Messrs. Bickford-Smith's over the
electricity we stated to be the greater certainty of
carrying fire through powder to the. bottom of the hole,
so as ensure ignition at the bottom, in order that the
force may be expended upwards. It is known that in some
instances the use of electric appliances by unskilled hands,
and under the awkward circumstances of underground
blasting,. has caused premature explosion and serious
accident. The instantaneous fuse, moreover, is more handy,
and, unlike electricity, is in no way subject to climatic or
atmospheric influence, and will remain immersed in water
forr considerable time without injury. It is said of Sir
Humphrey Davey that by his invention of the safety-lamp
he saved thousands of lives. Perhaps as much may be
said of Messrs. Bickford-Smith and Co., the original
inventors of the safety-fuse, whose work and name is
known wherever mining exists in every quarter of the
habitable globe. The cost of 60 feet of " instantaneous "
fuse, the patent " igniter," and about one yard of slow
safety-fuse, including carriage, was 6s. 9d., or about 4d.
for 10 tons of accomplished- work in the case above
referred to.