The Wheeling daily intelligencer. [volume] (Wheeling, W. Va.) 1865-1903, 1871-08-04
LIGHTNING RODS.
FFom the scientific American

FIom The scientific American.
In our paper for July |, We gave an ar.
llcIf on lightning rods, showing the
sizes, arrangements and earth connections
necessary lor the complete protection Of
buildings from the disruptve effects OF
electrical discharges.
In that article II was shown that the
grand defect in nearly all lightning rods,
as commonly put up, is the lack OF proper
communication between the rod and the
earth.
A building IL undoubtedly safer without
any lightning rod, than It is Il the rod be
not properly connected with the ground
Mr.. David Brooks, well known as the
originator Of the paratlln telegraph in
sulators, and u careful student Of clectrl
city, has lately published some useful oh
servatIOns concerning lightning rods,
from which we gather the following
When cloud passes over the earth II
becomes charged with electricity, and the
earth directly beneath the cloud Is charg
ed with The opposite electricity; bat dis,
charge or lightning depends entirely upon
the amount of electricity accumulated,
the tension of this accumulation, and the
proximity of this cloud to the earth.
The cloud Is sometimes charged posi-
lively, sometimes negatively, but what
ever the amount Of this electricity an
equal amount Of the opposite electricity
lssNccumulated in the earth or some
neighbOring cloud, or the opposite cleo
triCity may he divided or distributed
among other clouds and the earth.
The quantity and tension Of thunder.
bolt Is not Of such immense degree, that
unless an adequate channel or path IL
providcdas conductor disastrous results
are likely TO ensue.
The elect Of placing an iron conductor
or rod between the earth and the cloud,
Is to facilitate the discharge of the elec.
triCity from the ClOnd 10 the earth II
the cloud be charged with positive elec
tricity, the rod becomes polarized-that
II, II the cloud be charged with positive
electricity, the upper end Of the rod Is
charged with negative, the bottom por.
ton with positive, the opposite Of the
earth, which Is negative.
The ordinary rods extend into the
earth, hut the connection Is 80 poor
elcctrlcally--that Is, the connection has
so small conducting capaCity-that acCu
mutation Of electricity takes place, and
violent discharge 10 any other neighbors
ing object or conductor (as for example,
to the building to which the rod Is at
taChcD Is the result, 10 very nearly the
extent, a. ilthC rod were not touching the
earth. ~
The only method Of Obviating this diff.
Guilty Is 10 enlarge the metallic surface Of
the rod where 1t comes in contact with
the earth far more than Is ordinarily
practised.
All objects conduct, but In vastly differ.
ent degrees. For instance, iron conducts
only about one.siXth as much or as well
as copper. II has OnP.sixth the conduc.
tive capacity.
They conduct directly in proportion to
their sectional area, and inversely In pro.
portion 10 their length.
A bar Of copper that has one square
inch section, a foot in length, has the same
conducting capacity as bar Of iron six
square inches section and foot In length.
The conducting power OF iron Is one
thousand million times greater than wa.
ter. The ratio Of difference Is less In pro.
portion as the water contains impurities;
but If the moisture In the earth where sui.
phuric acid and water, In the proportion
ofOne OF water TO eleven Of acid, the best
conducting liquid known, the ratio OF
conduCtivity Ol this solution, compared to
iron, would be, by the determination oil
DIR. Matthiessen, as one TO one hundred
and slXty.six thousand; so that, making
all due allowance for the lmpurity ofthe
moisture on account of the acids and aka
lies contained, the ground terminal Of the
rod should expose surface In damp earth
at least equal TO the surface Of earth over
which the building stands.