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Kasum, Emil (ed.) / The Wisconsin engineer
Volume 52, Number 2 (November 1947)

Robinson, E.; Zimmerman, E.
Science highlights: lightning,   pp. 24-33


Page 24


Science Highlights:
                                                        Lightning
                                 by E. Robinson m'49
                                    E. Zimmerman e'49
Potent:
  Lightning originates in wind-
tossed clouds. The charge gener-
ated is negative, and a positive
charge follows along the ground as
the cloud is blown along. When the
positive and negative charges be-
come strong enough, a relatively
small current streams from the
cloud to the earth. The return
stroke, from earth to cloud, aver-
ages 20,000 amperes. It may reach
a peak of 200,000 amperes (one-
half amp. will light a 60-watt bulb).
It is estimated that cloud potentials
which start the lightning discharge
are higher than 20,000,000 volts.
Peculiar:
  St. Elmo's fire, while not a light-
ning stroke, is a visual discharge
resulting from high concentrations
of charges in the ground and in the
clouds. These discharges are called
corona.'" Lightning usually follows
St. Elmo's fire. An interesting ob-
servation of this phenomenon was
recounted in a recent letter to the
General Electric High-voltage Lab-
oratory, Pittsfield, Mass. It stated
that two boys were riding horseback,
one ahead of the other, when the
boy in the rear noted an unusual
glow outlining his companion's
head and the rump of his horse.
His startled ejaculation caused his
friend to turn. On looking back, he
observed a similar glow about the
other. It is presumed that the boys
partners in creating
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were elsewhere by the time the light-
ning struck, since they wrote the
letter.
Pernicious:
  Another letter received by the
Pittsfield  laboratory  refutes  the
claim that lightning never strikes
twice in the same place. The frus-
trated author wrote:
  "Last summer, I had left my
house with all the windows open,
doors open, my radio connected,
and the lights on.
  "On returning I found that light-
ning had visited us. The radio was
wrecked.
  "A week ago we were struck
again.
  "This time, I saw it all. I had dis-
connected the radio wire from the
outside antenna, had taken the ra-
dio plug out, turned off all the
lights and closed all windows and
doors. On entering the kitchen I
saw a ball of fire fairly dancing on
the porcelain table-top. I was so
startled I didn't follow its course
from there.
  " . . . our new radio was a sham-
bles."
Protection.
  High - voltage engineers believe
that lightning rods, when properly
installed, are extremely efficient.
Faulty installation and careless
damaging of equipment after instal-
lation are mainly responsible for
the failure of such a system when
approved materials and methods of
installation are used.
  As for those persons who are in
constant terror of Thor's bolts, a
lightning expert offers this homely
consolation:
  "If you hear the thunder, the
lightning did not strike you. If you
saw the lightning, it missed you.
And if it did strike you, you would
not have known it."
       (continued on page 28)
THE WISCONSIN ENGINEER
I
'Je. u.. ra - r
24


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