Evening star., 1901-11-02

stand a pressure from the wind of forty
pounds on every square inch of their sur
face. Each of the four corner posts of the
largest tower must stand a strain of nearly
seventy tons. Immense blocks of concrete
form foundation for each tower and also
serve as sort of anchor to still further
steady it.
Inch Thick Cables.
There is a variation in temperature of
about 60 degrees at the Straits of Car
quinez, and this Will cause variation of
fully FIVE feet in the sag of the great
cables. These cables are made of steel,
and are each nearly an inch in thickness,
there being about "A score of wires in the
twisted strand Any person who has ever
felt the surprising pull on a kite string
when the kite is high in the air will ap-
preciate that the fastening of the cables at
either end of the long span is ticklish
problem. For each cable there has been
provided an anchorage in the form of
mass of concrete almost large as an
ordinary room, and the great wire rope is
wound around a wheel a couple of feet in
diameter.
Four cables span the Straits of Car
quinez, but only three are in use at any
one time, the fourth being always held in
reserve. This enables the cables to be
cleaned or repaired at any time, and 1t
would be difficult to imagine a more ex-
citing task than that of the man who must
travel out over the eXpanse of water in a
tiny car suspended from the cable, which
he greaSeS as he slowly glideS below it.
Strangely enough the cables move less on
windy day than on a perfectly quiet one.
On morning when the air is still a per-
son can put his hand on the cables, when
no electric current is passing through and
feel a continuous jarring movement
whereas, IL he takes hold of the same cable
when a breeze is blowing, he will not only
md 1t free from movement but so abso-
lutely rigid that he cannot send wave of
motion out into the span, no matter how
hard blow he dealt to the great strand
of wire
Swinging the Ropes.
The spanning of the cables in their pres
ent position was of itself a novel perform
ance. After one end of cable had been
attached at the south tower the reel was
placed on self-propelling steel barge, and
this craft, assisted by a powerful gasoline
launch, was thus towed across the straits,
paying out the cable as it went A very
powerful little engine was used for pulling
the cables up to the height required 1t is
interesting in this connection to note that
when the sag in the cable was such that
1t touched the surface of the water of the
straits the strain was only 1900 pounds
but when the engine, after hours of steady
tuggtng, had finally gotten the cable into
the desired position, although less than
drawn in, the strain had increased to o.
500 pounds. All four cables were strung
without single mishap.
BY reason of the high bluffs on either
side of the straits the cables, where they
sag the most, appear to approach much
closer to the water than they really do
and this optical Illusion has given several
mariners bad frights. On one occasion,
when great ship laden with wheat was
being towed up the straits, her master and
the captain of the tug were so certain that
they saw destruction impending from the
great cables, which they had not discerned
until almost upon them, that the COM
mander of the tug, who was giving an ex-
cursion to several ladies from San Fran
cisco, hastily sent them all down into the
cabin to save them from being killed from
the spars and ships rigging, which he ex-
pected would be falling about them within
a few moments. The ships masts were $50
feet in height and the surprise of the men
on deck may be imagined when, as they
passed underneath the span, the masts
lacked full $50 feet Of touching.
Prior to the erection of the engineering
marvel at the Carquinez straits the longest
span on the North American continent
for carrying electric power over water was
that of an electric lighting company in
British Columbia, which spanned the Co
lumbia river in a sheer stretch of 1,5OO
feet. 1nasmuch as this new California
wonder swings through the air for three
times that distance it may safely be ac-
counted the most marvellous structure of
the kind on the globe.