Casco Bay breeze. [volume] (South Harpswell, Me.) 1901-1917, 1905-08-31

reports of committees hav-
oR ing been made public. The
first gives the results Of the lightning
research committee. which was organ
lied some years ago by the Royal Insti-
tute of British Architects and the Sur
veyors' Association, which deals prin.
cipally with the protection Of buildings.
The second was presented at the re-
cent meeting OF the National Electric
Light Association, i'm Denver, by Alex
Dow. and deals with the protection
OF electrical systems from lightning.
I'm neither report" says the Electrical
Review. "is there any particularly
novel suggestion, nor have the invest.
cations brought to light any new phe-
nomena. Previous recommendations
are upheld by the new evidence secured
by the, members of the committees
The report of the British research
committee is preceded by an introduc-
ton prepared by Sir Oliver Lodge. a
member Of this committee. In this in.
production he considers two types Of
lightning stroke. The first. termed
by him the A stroke. is one i'm which a
direct discharge takes place from a
charged cloud TO the earth. This dis
charge is not particularly dangerous.
To protect buildings from II, lightning
rods are useful. The points of the rods
may indeed prevent n violent discharge
by assisting in equaliz;ng. the potentials
OF the cloud and the earth. Lightning
rods. to be effective. must, however.
be installed properly. They should
offer path Of least resistance for the
discharge, yet the resistance of this
path must not be too small. II the rod
does not form the path OF least resist
ance. the discharge may leave 1t and
md its way to ground through neigh
boring materials. On the other hand. IL
the resistance of the rod be too low.
the discharge takes place through II too
rapidly-almost explosively-and Is La
bic to set up induced or secondary dis
charges in neighboring conductors.
The rod should be carried to the ground
with as few bends as possible. Iron
Is better material than copper, pro-
vided atmospheric conditions are not
such as to rust ii away too quickly.
"The other, or B type Of stroke, as II
Is called. occurs when an unchanged
cloud intervenes between the earth ard
the charged cloud. This intervening
cloud acts with the charged cloud as an
electrical condenser. and .vshes a dis
charge takes place between them, the
charge upon the upper surface is neu-.
tralized. and that on the lower surface
suddenly set free. and conssuuently
throws sudden strain in the dielec-,
trio between the cloud and the earth.
with the result that IL discharge
takes place, ii is ant to follow an err
ratio path. The effect OF such strokes
Is more serious than that OF an A
stroke, and lightning rods offer but
slight protection. The only way to
protect the building from such strokes
is to surround 1t by cage of metal.
1t Is suggested that powder magazines
be protected by complete metallic
sheathing; but. even metallic cage
does not guarantee a building against
lightning.
Lightning will sometimes prefer to
find its way to ground through the hot
gases Of tall chimney. rather than
through the rod provided for IL. II is
suggested that this might be prevented
by raising a number of rods we'll above
the top OF the chimney. connecting
them to the ground through vertical
wires. II is recommended that all me-
tallic parts Of building be connected
to good grounds: and although there
Is no record of damage to tall steel
frame structures IL would be desirable
TO provide n better earthing connec-
ton than that usually obtained through
the concrete foundation. The report
suggests that the usual method Of
grounding conductors by means or
large plates should ~ abandoned in
fGvor of n ground obtained through n
perforated steel spike driven into moist
ground. and flied with graduated
charcoal mot cokel.
"Tbe problem presented to electrical
engineers Is In some ways even more
troublesome than the protection OF
buildings from lightning. for in add
lion to providing n path for the dis
charge to ground. the lightning ar
roster must prevent the line current
from following along the path taknn
by the lightning. In addition. light
ming arresters used on electrical sys-
TENS are frequently depended upon to
protect the system from damage due
70 an unexpected happening taking
place on its own lines. A sbort.circuit
on transmission line, or sudden
throwing on Of large load. may set
M electrical oscillations which will
cause an excessive rise OF voltage. Will.
danger OF breaking down the Insulation
Of the electrical ma chinery. n the
lightning arrester bc adjusted 50 rs
to allow n discharge TO take place "
the voltage not only from che lines to
the ground, but between the lines
themselves. rises above n certain point.
~ viii act as safeguard. The engi-
pser OF transmission system does not
fear n direct stroke OF lightning as
much as induced or secondary strokes.
or excessive potential due to a static
charge. a direct stroke Will frequently
find its way 10 ground through the
poles. rather than pass back 10 the
n. =.