New-York tribune., 1869-06-02

building. The prejudice in favor of insulators
arises from misapprehension, Strictly speak
ing, there are no non-cOnductors; but that
term is applied to substances which conduct
very imperfectly and are subjected to violent
disruptive effects when shock of electricity
passes through them.
The insulation of telegraph-wires is frequent
ly referred to by lightning-rod men as exhib-
iting the necessity and usefulness of insulating
lightning rods; but the cases are not at all
parallel Currents of electricity of low tension
are used for telegraphing; and whenever dis
charge of lightning strikes the wires, it breaks
tho insulators and passes down the poles
to the earth, as the frequently splintered
telegraph-poles bear witness The object OF
insulating telegraph-wires is to postpone the
restoring of the equilibrium, by prevent
ing the electric currents from taking the
shortest course from pole to pole of the
battery; whereas the purpose of alightning-rod
is to promote the restoration of the equilibrium
as rapidly as possible. If the rod be insulated,
the "non-cOnducting" substance between the
rod and building intercepts and stops the flow
of currents of rarifed electricity from the
building to the rod, and thence to the atmo-
sphere and vice versa, thus permitting con-
tinued disturbance of the equilibrium Of the
building, under the influence Of a thunder
cloud,n until discharge of lightning takes
place. Then the fluid has sufficient force or
tension to overcome the obstacle which the in
sulators present, and an explosion into or from
the building is the necessary consequence. Of
course, the quantity of electricity required to
restore the equilibrium of the building is small
Al, .l,oIo I.ao1,a ,nrhin
come from cloud thousands of acres in ex-
tent; but it is enough to do injury If it comes
all at once and in high state of tension.
To insuate the lightningrods therefore, is to
fasten the safety-valve and render it inOper-
ative.
To prevent discharge from leaving the rod
and passing through the building, something
more must be done than to attempt to keep 1t
out by erecting such a fimsy and insignificant
barrier. The rod must be arranged so as to
present points for the reception and discharge
of electricity at the extremities of the build
ing, both above aud below, and the different
terminatiOns in the ground must be connected
by rods lying across the roof, so that lightning
can be provided with path in horizontal dlT
rection, which, being continuous, will be pre-
ferred to any series of detached masses Of con-
Quoting matter contained within the building
In construction and application, lightning
rods should be simple, substantial, and durable
aud any metal is sufficiently good conductor
for the purpose. The difference in the con-
ducting power Of iron and water which ranks
next to the metals as a conductor, is, according
to Cavendish, as millions TO unity. The rela-
tive conducting power of different metals is,
therefore, not worth considering in this con-
necton hence iron is used for the telegraph
instead of copper, which is theoretically better
conductor than iron. A lightning-rod made of
the precious metals (Which are the best con-
ductors) would not be effective if it were i'm
properly located and arranged. If rod of
any metal be rightly constructed and judicious-
ly applied, there is no danger Of a discharge
of lightning leaving it for any less perfect con-
ductor within the building, and it is only those
substances which are poorer conductors than the
metals that are injured by the passage of
electricity upon them.
To be hypercritical, iron may be said to be
the best metal for lightning-rods, because the
rusting of its surface, which does not materi-
ally impair its conducting power, produces
numerous sharp points, which answer to re-
CelYe or d1SpcrSe eleCUlClIy us may Do IequlICu'
Every one can understand why the upper ex-
tremity of a rod is pointed, and on reflection
should easily perceive the usefulness of other
points at intervals along the line of the rod.
If it were true that lightning-rOd should
have perfectly smooth surface, it would OBJ
yiousy be equally true that it should be sur
mounted with globe or ball instead of point.
The function Of the points on lightning-rod
is to increase its capacity to receive or dis
perse rarifed electricity when the locality is in
state of electrical activity, owing to the
prevalence of a thunderstorm.
The operation of the points is substantially
the same whether the currents of electricity
are flowing from the earth to the atmosphere
and clouds, or rice versa and these currents
tend to circulate with the greatest rapidity and
intensity just previous to discharge of light
ming. The lghtning-rod, therefore, should
have an intimate connection with all matter in
the vicinity, and be SO cOntrived as TO have
the greatest attainable capacity to promote and
facilitate the circulation Of rarifed electricity,
so as, if possible, to forestall the discharge by
restoring the equilibrium silently.