Martinsburg gazette. [volume] (Martinsburg, Va. [W. Va.]) 1833-1855, 1845-09-18

| ia the dimensions OF the cloud. Experl-
ence, however, does not justify this, On
the contrary. thunder clouds have been re-
peasedly traversed with impuaiiy. 10 Au-
gust, I770, the able Richard through
a tssunde- cloud 90 small mountain near
Bouer, between Chalons and Jonrnus.
Before be entered the cloud the thunder
rolled as il is won't 10 do. When he was
developed in It, he heard only single claps
with intervals Of silence without roll or
reyerberation. After he passed above
The cloud, the thunder rolled beloic him as
before, and the Lightning flashed.
The sister OF N. Arago witnessed simi.
liar phenomena between the village Of Es-
Hagel and Limour and The officers and
Engineers engaged IN the trigonomelrical
survey repeatedly experienced the same
occurrences on the Pyreaees.
The parctonnerres, appended 10 bull
dings and ships, consist Of a pointed me.
,allic rod, attached to, and projecting up.
ward from the highes! poin; OF the struc-
tufe placed under their protection. The
lower end Of this rod is connected with a
series Of other metallic rods, or with a
metallic chain, which is continued 10 the
grouad. If The paraionnerre be spplled
10 building, the series Of rods beng at
tached 10 the walls and carried to the
ground, must be continued to such depth,
and brought 10 such position, that its in-
Iferlor extremity shall either be immersed
in water, or 10 soil which is in perma-
nent state of moisture. The water, or
moist soil, possessing the conducting pow
ef, receives the electricity from The ex-
tremily OF tue rod without explosion but
/ If the rod terminated in dry earth the flu.
ia would escape from the extremity, or
worse still, from some other part Of the Sc
rles Of rods, with an explosion, and would
damage whatever bodies might be ada
cent to it. Il IT be applied to a ship, the
pointed rod is attached to the point Of the
ma n.top-mast, and the lower end OF the
rod is connected with a Chain which is
carried down the mast aud rigging over
the side OF the vessel, and finally plunged
10 the sea. The highest point of the rod
being liable to be heated by lightning,
and to be oxyda,ed, is formed by platinum,
or gilt, so as to restrict oxydation.
That paratonnerres exert their protec-
tive power only when lightning strikes tie
structure over which they preside, is an
error easily corrected, by immediate ox-
pertinent, independently Of the reiutatIon
it might receive on theoretical grounds.
Let the continuity of one Of these appa-
raIuses be broken, by separating any two
bars OF the series, so that their ends, instead
of being in immediate contact, shall be
distant by the eight or tenth part of an
inch from each other. When stormy
clouds pass over the apparatus, contin.
ual stream of electrical light will be wis.,
BILE 10 the interval between the separated
points of the bars. II their distance be
increased to an inch, sparks will be obser-
we'd to pass between them, in rapid and
continual succession. accompanied by de.
donations ss loud as the report of pistol.
Captain Wynne, who commanded a
British frigate, lately observed, during a
storm, at a point where, by accident, an
interruption OF the metallic continuity OF
his qaratoGneTre occurred. an almost IN.
iutermittIng succession of sparks, which
continued for Two hours and half, the
whole interval during which the thunder
clouds were over .he vessel.
1t is apparent, then, that paratonnerres
are not merely Instrumental iii saving a
structure when lightning actually fall upon
1t, but they alsopossess preventive pow
er, and gradually and silently dsarm the
clouds by draining the electric fluid from
them; and this process commences tae
moment The clouds approach position
vertically over the paratonnerre.
An ingenious calculation of the quaint
ty Of lightning drawn from the clouds by
psfatonnerfes, has been made by NJ. Ara
go. lie states that in an ordinary storm
hundred sparks would be transmitted
through small break of continuity in
the conductor OF which the combined ef-
feet would be sufficient to kill man, and
these would pass in ten seconds As
much lightning would, therefore, pass per
minute as would destroy six men; and as
much per hour as would kill three hun.
dred and sixty men. He calculates iu
this way that the paratonnerres erected by
| Becceria on the palace of Valentino,
combined with the effects of the pointed
parts OF the roof, must take MS much light
uing per hour from the clouds as would
be efficient to destroy three thousand
men.
The quantity of electricity which point.
ed conductors neutraize, may be imagin-
sd from the following circumstance The
British frieate Dryad, provided with
paratonnerre, Constructed according 20
the method proposed by Mr. Snow Har-
rs, by fixing TO the mast itself narrow
plates OF thin copper,) was several times
exposed 10 violent tornadoes of'ihe coast
OF Africa. The electric fluid was seen on
every part Of these copper plates in such
quantity as to produce around them sort
OF luminous atmosphere, accompanied by
noise like that Of water boiling violent
ly.
10 the practical adaptation OF paraton.
nerres, the determination OF the range of
their protective influence is a problem of