The National tribune. [volume] (Washington, D.C.) 1877-1917, 1892-02-18
dsnsion The NaHonsi Trib1aA
THE WEATHER.
The Protection Of Life ,nd Propsrey from Light
Mag.
Continued
By LrEUr. ]. P. FINLEY, U. s. SIGNAL SERVICE

By LTECT. J. P. FINLEY, Z. :. SIGNAL SERVICE.
It is n remarkable testimony to the genius Of
Franklin that since his time no material altera-
ton in the design Or the construction Of the
lightning rod has been adopted
The lightning rod as ne invented il, when
the science Of electricity was in its infancy, is
practically the rod in general use to-day.
Franklin discovered that through the elective
power Of metallic points the action Of terres-
trial electricity could be, in a measure, con-
trOled FOR the protection Of buildings. The
lightning rod was probably the earliest appIi-
cation Of electricity 10 a useful object. It may
be said 20 consist Of three essential parts, viz
o. A root. earth connection, or underground
portion. ~ A stalk rod, band, tube or wire
rope proceeding from the root more or less
vertically up the outside o! building. ~ A
point surrounding the apper extremity Of the
stalk
The scope Of lightning rods, although Of
most beneficial nature. has never been con-
nected with economical or commercial necessi-
ties 10 sach an extent 20 develop the art OF
lightning engineering except TO a very mod
crate degree. There seems but little doubt
that Franklin's fundamental object was to
elicit the charge from the ground by means of
the lightning rods pOiEt, and that the idea Of
Offering the lightning an gasy conduct to the
ground By means Of tho stalk was the result of
q later conception Of the theory Of the rods
actiOn-a conception that probably received an
impetus from The greater knowledge OF electri-
cal currents that accrued from the labOrs Of
Volta and his successors.
At the present time the lightning rod is gen.
orally held by physicists 20 possess two func-
tiOHs-One by means Of the root and point
tending 10 prevent thuuderb0lts and the other
through the mediam OF the stalk, tending to
facilitate their passage after they had occurred,
so that they should effect only minimum Of
injury. The latter function is the one which
has been most really adopted by the general
public as embodyiHg the fundamental princi-
pies Of the lightning rod.
The general superstition appears to be that
Franklin. with his kite, drew lightning from
the skies, and by thus developing it under con-
troll was enabled to identify it with the electric
spark. Further, that then, by analogy Of
reasoning, he conceived the idea Of fixing metal
rods to buildings, in order that if the lightning
struck them, il might be drawn down the vet
cord Of his kite. What really happened, how
ever, in the case Of FrJuklin's kite was this:
During the progress Of a thnndcr storm, the
point that surmouEtcd the kite elected cleo
triCity f:Om the ground in the visible form Of
an electric spar!, leapiHg across an air gap Of
slight length, purposely left in the connection
OF tho kite apparatus with the earth. This ap-
paratus was simply a species Of lightning rod
and the great elevation given to its point by
the kite arrangement was quite unnecessary, as
was proved by VAGbard who, at Frankln'5
iustigatiOH, produced the same results by
means Of pointed iron rod Of no great hight.
What Franklin saw was not lightning, nor has
anyone ever Intentionally drawn Lightning
from heaven, or created thunder bolts. Frank
Inns experiment only tended to confirm the
precGHceived idea that lightning was associated
with electricity, and was probably huge cleo
trio spark; and it proved that pointed metal
rods had the power Of ejecting electricity from
the ground, at all events whilst thunder
storms were in progress, and the result was the
conception Of defending buildings by means Of
these rods.
There is hardly any doubt that the suppo-
stiOn OF lightning passing down Lightning
rods into the ground arose from the prevalent
view that its direction was invariably from the
clouds TO the earth. That Franklin himself
gradually fell in with this theory of the
function Of lightning rods is almost certain, and
the probability is that after he had established
the practice Of his invention, he had neither
inclination nor time 10 attempt to elaborate its
theory.
At tho present time there are two schools
among the authorities on the subject of pro-
lection against lightning. The chief school,
comprising the great majority of physicists and
engineers adopts the plan OF embracing the OBJ
feet 10 be protected in a network Of metal, so
rs 10 bring it as nearly as possible into the con-
dition Of a metal object In this system the
stalk OF the rod is metalliCally connected TO all
the metal surfaces on the building. thus Afford
ing an easy passage to the root in the earth.
The other and minor school recommend that
the stalk DO insulated from ali metallic surfaces,
and thus make the course TO the earth of the
thunderbOlt as direct rs possible. This school
holds that metallic connections with the stalk
are superauous when the rod is in good order,
and dangerous when it is not.
Ito be cOntinusd.l