The Western news. [volume] (Libby, Mont.) 1933-current, 1942-07-09
New Focts
About Lightning
By HI. t. Osborne

By H. T. Osborne
MISSOULA. July There are
many more phases of the forest
fire problem than our Experiment
Station Division of Forest Protec-
ton is or should be financed to
study. One of these includes the
fundamental characteristics of
lightning. While the nature of light
ming is one of the most talked about
features of the forestfire problem.
and while we can always do more TO
control a menace which we under
stand than one which IS mysterious
in its behavior, the study of mil
lion-volt lightning bolts occurring in
a few mllionths of a second is
clearly field for the electrical en-
gineers. not foresters.
The Experiment Station has
definite responsibility, however, to
keen informed of progress in this
field and to relay significant inform
alton To fire control officials. We
have been fortunate in that respect
by obtaining the personal interest
of DR.. K B McEachron, director of
the high voltage research laboratory
of the General Electric Company at
Pittsfeld. Mass. One of his assist
ants DR.. f. A Evans, worked one
summer as fire-weather observer at
our Priest River branch station.
Both of these men appreciate the
vital part which lightning plays in
the northern Rocky Mountain job
of forest fire control.
Recently Dr.. McEachron furn-
ished US with summaries of some of
their studies, largely made at one
of the most ightning-struck spots
in the United States, the 1,250-foot
Empire State Building in New York
City. The most significant and most
interesting findings, to Us, are as
follows
Two Kinds of Lightning
|. Fire control men have long
eontendcd that there are two kinds
of lightning, generally fire-starting
and generally NOTWITHSTANDING
Eleven years ago Seley w Moore of
Darby. Mont, lookout for two
years. reported his observation that
red lightning. though often tearing
trees TO pieces, seldom starts fires,
while the bluish-white type is US
ually effective DR. w. J. Humph-
reys of the Weather Bureau ex-
plains this, in the December 1881
issue of the Monthly Weather Re-
view, as possibly due to the fact
that "a lightning discharge through
heavy rain may we'll associate some
of the water. or water vapor. along
It's path. and thereby produce
the hydrogen spectrum, which is
brilliantly red A flash through
the dry air on the other hand emits
light due almost entirely to the
oxygen and nitrogen Of the atmo-
sphere, and is primarily white or
blush white Humphreys conelud-
cd: In short it is not the differ
ence between white lightning and
red lightning that makes the one
a greater fire hazard than the 9th
er, but the condition. wet or dry,
of the combustible when struck.
Too many of US have seen too
many forest fires started by light
ming during and after drenching
doWnpours to accept this as a COM
plete explanation. Fuel moisture un-
doubtedly determines whether or
not the fire will spread, but light
ming continues to tear trees to pieces
on dry days without starting fires,
and it continues TO start fires when
the woods are SO wet that the
smokechasers have to hurry or the
fire will 60 out before they get
there. Obviously there must be
other kinds of lightning" besides
red and white.
I DR. McEachron reports that their
photographs, taken on film NOV
ing past the lens at l24 to 2l8 feet
per second show that there are two
other kinds. Cd the so-called single
stroke which. once the path is es-
tablished, occurs in only few mil
lionths of a second. and (2) the
continuing type which sends bolt
after bolt crashing along the same
path. He states: 1T is the contin
uing type of lightning strokes which
persist for fractional parts of sec
onds which cause fires, rather than
the 1lBH-tulIGilt. SilOl v tliliC dlS-
charge lasting but a few mil
lionths of second) which blow
trees apart
2. Although the human eye and
brain cannot distinguish between a
few millionths and few more mil
lionths of a second, the bulk of the
continuing type of flash can be
distinguished because the average
repeater lasts for nearly half sec
ond. The record-breaking stroke. so
far measured, consisted of flashes
repeating over the same path full
liz seconds.
Coupling this with Humphreys
deduction, it appears that the long
duration white flash is definitely
our most dangerous type, while the
extremely short red flash is prob
ably only rarely fire starter.
8. From their photographs of
lightning striking the Empire State
Building. DR.. McEachern reports
Every stroke but two of which the
author has record, either struck the
highest point on the building or
outside cone the base radius of
which at ground level of the build
ling was equal to the building
| height y Poles bearing lightning ar