The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1872-08-03
Scientific
From The Scientific american.
Lightning Rods.

Lightning Rods.
Lightning Rods and how to con.
struct them" is the title ola convenient
little handbook by Professor John Phin.
1t contains much useful information
upon the subject, aud ought to have a
very wide circulation The following
selections will give some idea of the
excellent character of the book
Are Lightning Rods Really a Profec,
ton There are many instances on
record where buildings protected by
rods have been struck aud injured.
But this is not to be wondered at when
we reflect that fully one-half-uay, per-
haps three .fourths-of all the rods now
actually erected violate the fundament.
al principles upon which their efficiency
depends. Besides serious errors 10 re.
gard to arrangement and continuity, it
will 10 general be found that it is only
by the merest accident that a good
ground connection is ever secured
This point will be more fully discussed
in subsequent paragraph. Meanwhile,
the following facts prove irrefragibly
the great value Of well constructed rods.
The Cathedral Of st. Peter, in Geneva,
although so elevated as to be above all
other buildings in the neighborhood,
has for three centuries enjoyed perfect
immunity from damage by lightning /;
while the towerof ST. Gervaise, although
much lower, has been frequently struck
This doubtless arises from the fact that
all the towers Of ST. Peter are accident.
ally furnished with perfect conduction.
The great column of London known as
the Monument, erected in 1917 in COM
memoration Of the great FIRE, although
over two hundred feet in height, has
never been struck while much lower
buildings 10 the vicinity have not es.
capped. The Monument, however. is
protected by most perfect conductor,
the upper end terminating in vase
from which proceed numerous metal
plates designed to initiate the appear
anee Of tongues of fame. The vase
communicates by means Of stout bars Of
iron with the metal staircase, which
lescends through the middle of the
column aud terminates in the ground.
4 still more striking instance Of the
value Of lightning rods is a church on
the estate Of Count Orsiui, in Oorinthla.
This building was placed upon an emf.
neuce, aud had been SO often struck by
lightning that il was deemed no longer
safe to celebrate Divine service within
its walls. In 1880, single stroke Of
lightning destroyed the entire steeplc
after it had been rebuilt, it was struck
on an average four or five times year,
without counting extraordinary storms,
during which it was struck from Eve tc
ten times 10 a single day, Ia 177s, the
building was reconstructed aud furnish
ed with conductor; aud according tc
Liehtenberg, up to l7S3-that is to say
during the space Of five years-thC
steeple had been struck only once, and
this stroke had fallen upon the metallic
point without producing any damage
For two or three years after its erection
the church Of st. Michael 10 Charles
town had been frequently damaged b,
lightning; conductor was attached
to 1t, aud during the following four
teen years it had not been injured -
The steeple Of ST. Marks, in Venice
has hight oil $40 feet, aud was fire.
quertly struck by lightning until ,
proper lightning rod was applied to it
since which time it has not been injur
ed. These facts leave no room fcl
doubt in regard to the great value Of
lightning rods.
Tie Best Form for The Rode VIC
examine the rods ordinarily found in
market, and pulled BY those who have
invented them, we shall find that, in.
stead Of being solid bars Of a square,
round or merely faltend form, they arc
tubes, twisted ribbons, or bars whose
cross section has the form Of star.
Aud it We ask why these complicated
aud expensive forms have been adopted,
we shall be told that it is for the pur-
pose of obtaining the greatest amount
of surface with the least amount of met
al, and this is done because electricity
always resides on the surface. Those
who reason in this way, however, prove
clearly that they have never studied the
subject, else they would be aware OF the
fact that while static electricity, as it is
called-that is, electricity at rest-al.
ways disposcs itself on the surface Of
bodies charged with il, electricity in
motion pervades the entire substance OF
the bar through which it passes, and
consequently the power OF such bar
to convey electricity is measured by the
quantity Of metal that it contains, aud
not by the extent of surface that il
presents. Pouillet showed this in a
very clear and decisive manner. He
measured the conducting power of a
fine wire Of cylindrical form-the form
that presents the least possible surface
in proportion to its cubic contents--
aud then, having flatteued and annealed
it, he tested it again. Its surface was
enormously increased, but its power to
conduct electricity was lessened rather
than otherwise this dimiuution being
probably due to the fact that the wire
was increased in length, and, conse
queutly its cross section was somewhat
diminished. An experiment, equally
decisive and perhaps somewhat NOR,
| aaaily narInrn,a1 "a a. H. .,............I ..