Year: 1859

will here state that / have used wire ca
bles as ties IN connection with cast iron
girders, because | have learned by actual
tests that this notion of the tensiveness of
wire, is, like many other opinions held
on mechanical questions In high quarters,
erroneous.


1t may appear at first sight that the
application of the serving wire is not
economical, as it does not add directly TO
the tensive capacity CT the cable; but as
il serves to protect the whole, its appiica-
tion is. on the whole, economical, as we'll
as most important. Then, if there should
be occasion for il, such a cable can be ta-
ken up by UNDERMINING, from nearly
as great depths as those TO which it can
be put down in safety. which will appear
more clear when it is understood why
twisted cable cannot be raised from any
great depth-which is, that In under
running, the concentrated strain In the
part near the ship drives the twist before
II, as it moves along, down into the lower
and less strained part of the cable, caus-
ing This part TO revoive and form into fes-
toons or balls of such weight as to part
the upper and unnaturally strained part.
and there will OF course be an " enc" of
1t. A cable of straight construction cam
not fail from any such causes.


That a twisted cable does become
thus distorted, there can be DO doubt; for
all the reports show that the spiral-lay
becomes Strengthened near the ship, where
the strain is greatest. Then, of course,
whatever winding Is driven out of this
part, must De thrown into some other
part; and that it cannot be thrown into
the part on board the ship is quite plain.
Ii must, therefore, be sent down into the
lower and less strained part.


That this is so, the reports Of the
appearance Of the cable, after hauling it
in, shows most conclusively.


Braided cables are without doubt an
improvement over the twisted form, but
their construction too is of yielding ma
ture. The wire itself may not yield In
length, yet the direction of the strands is
not straight, nor can they be applied to
the core with such tightness and compress
sion as is required for perfect protection.
1t will therefore yield considerable in
length when strained tensively, in con-





wire to take a straight form, and from
the compression of the core, which may
prove fatal.


Therefore the sIaight wire, well
and tightly served, seems TO be the only
reliable form Of construction, and it is
probably as cheap a mode as can be de-
vised for great depths. Such cables may
of course be made TO carry more than
one conducting wire, and of any size and
strength that may be desired. For shore
ends, they may be served with large
wire, and thus form a surer protection
than large wires twisted in the usual
form of ropes, Hemp twine might be
substituted for the wire serving, or strcng
hemp webbing nigh; do; but these can
not answer as we'll as annealed wire,
though the hemp may be cheaper. A
cable of straight construction is not quite
as flexible as one that is twisted, but 1t is
sufficiently so for coiling and paying out
over drums OF moderate size, and in these
operations the straight has several prac-
teal advantages over the twisted, which
[ will not now take time TO explain