The farmer and mechanic., 1911-07-04
PROTECT BUILDINGS
FROM LIGHTNING
BY PROF. r.. :. kEENE.

each summer. In the violence OF an
atmospheric electrician disturbance, ac-
empanied by awe-inspirinS flashes
Of lightning there are few who nave
not desired the protection OF isht-
ming proof shelter.
The prola abifty OF an ,ndivldual
building being 81 ruck by lightning IS
really very slight but there is always
a possibility Of such an occurrence
and also that the stroke might be at
terded with considerable violence,
mere than that the building might
take fire.
That lightning rods are real p"o-
lection to buildings from llghtnlns ilas
been proven so many times that thclr
value is no longer questioned, but lie
possibility of obtaining eXperim men.al
data is 50 limited that definite rules
for the esta ablishment of the rods and
conductors have never been formu-
Ia ted. For many years, lightning rods
were Locke ed upon with suspicion in the
country, because their sale for con-
sidera ble period was used as means
to defraud the unWary.
The formation of lightning is very
imperfectly nderStoOd but experience
With its Nagaries and knowledge OF
the laws of high-tenston electric cur
rents has established d fairly good
understanding of the methods Of con
structing lightning conductors f3r q. i
ordinary discharges. 1t very we'll
known that lightning is the discharge
Of d large amount of electricity in
very short space of time and that
whatever affords it a passage to the
earth is apt to be badly dam aged, un-
less the vehicle happens to be a good
conductor Of electricity and of suf
ficient size TO transmit the amount OF
electric energy the flash contains; in
w
damage at all.
AS storm develops the electrically
charged clouds pass over the earth
and when the electrical intensity be-
comes great enough to break down
the resistance of the intervening air
the resulting discharge will pass into
the earth by the most convcHiert
path. This is com monty some high
object of the landSca Pc, a building, a
pole "a tree or amy other object that
extends up from the earth. If the OBJ
Ject is a conductor of electricity and
connected with the earth, the light
ming will pass into the ground without
the least damage being done but If 1t
is not a good conductor the havoc that
is wrought in an instant is som etimes
appalling
Buildings with metallic roofs that
are properly connected with the earth
are far better protectors from ligbt-
ming than could be given by rods
Buildings that are completely covered
with sheet metal and we'll connected
with the earth are practically light
ming proof. Covered in this namnar
buildings have been known to be re-
peatedly struck by lightning without
the least damage. The sheet-iron
Sranary, SO common in the west when
well connected with the earth may be
considered lightning proof The ground
a h
made Of metallic rods that extend we'll
into the earth and securely fastened
to the metallic covering of the build
ings.
In considering the form of light
ming conductors it is we'll to keep in
mind the fact that a metal covered
building Well connected with the earth
is practically lightning proof and
that one with a metallic roof we'll
grounded is eXcellently we'll protected
ii not perfectly safe. If then. the roof
OF a building possesses a metallic ridge
eare-troughs and down spouts these
will afford Very good protection if
they are all connected and we'll
grounded. A roof covered with a
metallic screen, as a chicken screen
makes an excellent protector when
properly grounded
1t must be rem EN- bered that the
ground connection is a positive neces-
Hity anu too Hiuch care cannot De
exercised in its construction. The
earth IS the great reservoir of cleo
trical energy and it is al ways at zero
potential. If a discharge of lightning
can be directed into the moist earth
by a conductor its energy is soon
dissipated but the ground connection
must be of considerable area and ex-
tend we'll into the moist earth
piece of galvanized iron pipe driven
into the ground seven or eight feet
makes a good ''ground.' Large build
lngS must have two or more Such
grounds The connecting wires must
be securely fastened to the ground
connections.
In the matter of conduc citing wires
the y. ). W Gather Bureau recommends
a number three, galvanized iron wire
AS amply sufficient in size for ordinary
lightning protection. If metallic down
SrnQutS nSad cona,,o+o..c