The Brookings register. [volume] (Brookings, Brookings County, S.D.) 1903-1971, 1909-06-24
LIGHTNING RODS.

bolt, has been asked of the State Fire
Marshals' association of America BY
farm mutual insurance companies re-
Gently organized TO insure rodded
buildings only, and by companies who
have determined to increase the as
sessment or lessen the amount paid,
for unrodded buildings in case OF loss
by lightning. Fortunately, nearly
every rod now offered, if installed as
indicated below, will fill the require
ments.
In France the lightest galvanized
steel rod permitted is three-fifths of
an inch square. A rod of copper
must weigh, according to the scien-
lists of Germany, as much as a cop
per wire one-third of an inch in d.
ameter.
1t must be run from permanently
moist earth up to and along the comb
Of the building and down to perman-
emily moist earth.
A section of rod, securely held
erect. must rise from the circuit, a
height of five feet every 20 feet along
the roof comb and there must be n
rising alb We and close besides each
chimney, or other prominence.
On each upright section must be
one or more tips of a metal that will
stay bright.
The rod must be held away from
the building-not nailed to it.
To disregard any one of these
''musts" is to- seriously impair the
value of the rod. A rod that in any
way fell short of these requirements
would not be worth putting up.
The metal in a rod should be shaped
so as TO give it a large surface because
the current caused by a thunderbolt
is Of a sort that travels near the
surface of a conductor. This is call
ed skin effect" for the electricity
crowds into the one thirtieth OF an
inch next TO the external surface.
Many lightning rod agents believe
and teach that electricity travels on
the outside of a wire. 1t certainly
cannot.
A steel rod is rolled in a star shape
and galvanized. Another rod is made
by rolling sheet copper over star
shaped steel. This gives a copper sur
face and q metal cor to take up heat
into which the energy of the flash is
converted. All other copper rods are
made of many wires in order that
they may have large surfaces. The
way in which the wires in copper
cables are twisted or woven does not
effect the capacity of taking care Of
lightning strokes. An ideal rod. so
far as c~onduction is concerned, would
be one in tape form but it would be
inconvenient and liable to accident.
Cloud electricity forces its way
through the air to reach the under
ground water which feeds our wells.
A rod is worthless if not run down to
where there is permanent moisture.
In most localities this depth is s to
10 feet. In rodding an expensive
building it is desirable, but not neces-
sary to attach a mass of metal to the
end of the rod.
A section of rod must rise well
above the chimney for the moisture
in smoke weakens the resistance of
the air to electricity. The kitchen
chimney, above all others, should De
protected for it is the one most used
in the thunderstorm season.
There is no we'll established rule in
regard to connecting cutters. saddles,
rain spouts and other metals on a
building to the rod by wires. When
a rod is struck there are oscillations
and ~surgings of electricity in its
neighborhood, so a spark may be
given off by any metal near by. If a
rod runs within a few inches of metal
that is not grounded. the practice is
IA,a ra- snA- nlA~X,1
not be connected to the rod.
The greater the number of points
the greater the silent discharge from
the rod to avert a stroke, and the
greater the gathering power of the
rod if a stroke does come. Therefore
to use cluster of points is wise.
The fact that many Of the long slen-
der points are melted when struck,
shows that they should be made
thicker at the expense of length.
Glass insulators hold a rod we'll but
electricity does not leave metal to
run on siding or shingles even when
they are rain-wet.
Before sawmills had removed the
tall timbers, lightning struck trees
rather than houses. A tree trunk is
a bundle of pipes full of water, which
is one of the best conductors, and all
trees that grow tall, have a tap-root
reaching to permanently moist ground.
| Because wood is not a good conduc-
tor, a tree is often torn asunder by
part of the energy of the thunderbolt
being converted into heat. which
changes the water into it to steam so
suddenly that its expansion rends the
trunk.
Frank A. Craft,