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

presence OF large masses Of metal. such as
lthe guns in battery, or the machinery
used in certain large factories. or the ar
lmameni Of ship of. war, or the engines
lof large steamship
Theory affords no grounds for the law
laid down by NJ. Charles, AID observation
is not wanting to show It's iallscy.
The foremost of the ship Endymion
was struck by lightning at Calcutta, il
March, 1912. The malnmasi, not fifty
feet distant, had hain-condoctor, which,
according to the above law, would protect
d circle Of one hundred and fifty feet d.
ameter.
4 TIE bow OF the ship Etns was struck
at Corfu, January, 1880, although the
nslnmsst had chaln-conducior. Olbe-
cases OF similar character have occurred TO
buildings on shore, one Of which has re-
Gently been communicated TO the French
Academy. NJ. Arago, and many with
him, were unwilling TO admit so vague a
law, and experience confirmsthelr decision.
To protect an extensive building, several
Epara,onnertes would be necessary. and the
less the height ofeach the greater should be
their number, which, as well as theirposi-
ton, mus. be determined by the condition
that no par, must be more distant from the
foot OF the rod than twice lis height.
Although lightning falls generally by
preference on the highest points, of build
ings, it doesnot alredysdo so. Many cases
are recorded in which, without damaging
the summit, II has struck at the middle of
the height. Ia some cases il hes been seen
distinctly TO remove in the horzonthl d.
Ireclion, and strike the side Of asieeple.-
Cases are also cited in which il has enter
ed by the ground-foor where il has struck
persons and caused Their deaths, dong
slight damage to the first floor, aud none
TO the higher parts oil the house. Such
facts suggest the utility of paratonnerres
vita points presented iaterally and OBJ
llquely.
10 some countries the superior extremi
ties of paratonnerres are formed into a
group OF points, radlatlng in various direc.
tons like star. This method has been
suggested by the supposed advantages Of
horizontal and obIqae points. Expe.
renee has not yet supplied data on which
any certain judgment can be formed as TO
the efficiency Of this expedient.
The rod Of paratonnerre, by which ii
is intended to conduct the electric infu.
ence to or from the earth, should be Of
such thickness that it may not be fused
by the most powerful current Of electriei-
~ which is likely to pass through it,
Experience indicates that this purpose will
be sufficiently attained if it be square Of
three quarters Of an inch in The side, or
a circle of the same diameter. Towards
The base, an increased thickness is some-
times given to 1t with view to its stabil-
Iity. Paratonnerres are sometimes paint
ed to protect them from rust, and lamp
black is selected as the material Of the
paint, 10 consequence of its conducting
power.
1t has been already stated, that the in
ferior extremity ofthe paratounerreso ought
TO be immersed IN water or in wet soil. -
lift is necessary 10 add, that if it be in
water an artificial cistern will not serve
the purpose, as II is 10 general stanch, and
enclosed on every side by non conductors
of electricity. Examples Of the inefficien-
cy of such a termination 10 the conductor
are not wanting. Tbs cathedral of Milan
was struck by lightning on the 9th of
June, 1919, and the lighthouse a. Genoa
on the 4th Of January, 1927, and in Doth
cases damage was sustained, notwithstand-
ing the peratonnerres. On examination,
it proved that the inferior extremitIes OF
these apparatus were immersed in artiiici-
al cisterns.
To increase the surface of contact OF
the conductor with the ground, IT has been
proposed to make it diverge into several
points at its lower end, or TO fiat,en it in.
TO thin broad plate. 1t has also been
proposed TO immerse in bed Of charcoal,
previously raised to red heat, this being
a good conductor OF electricity.
When several paratonucrres are erected
on the same building, each should com
muncate with the ground by The near.
est and mos, direct route tine amd by such
means passing more freely through them.
Their efficiency will be st lImore augment
ed If they communicate with each other,
end with all the metallic parts Of the roof
Flexible metallic wires combined to-
gether so as to form metallic rope, such
as are sometimes used for suspension
bridges, have been proposed as substitutes
for rigid bars in para,onnerres as being
more capable Of adapting themselves to
the inequalities OF buildings, and less LA.
bic to lose their metallic continuity by the
effects Of rust.
When iron beams or cramps are used
in the construction of a building, they are
sometimes carefully separated from the
paratonnerres by non-ductors, such as
resin or pitch. If the paratonnerres be
properly constructed, this precaution is
unnecessary. The lightning will 60 TO
the earth in preference to any lesser mass
of conducting matter.
In tho adaptation of psraionnerres 10
powder-magazines, danger is supposed to
arise from the electric sparks, which issue
at parts oftbe conductor where minute and
Iimperceptble breaches OF continuity may
take place. The sparks, catching the
l n,suIar oh ,,ax, 10 occ,dapt.il,,