Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-07-06
Single Flash Represents But
One 0ne-Thousandth of KiIo-
watt Hour of Current.
MARKING BY BOLT FORMS
PECULIAR PHENOMENON
Bureau Of Standards Makes Study
of Cause and Effect of Storm
Accompaniment.
BY THOMAS r. HENRY.

only three hundred-thousandths of a
second. So it represents only eight
thousandths Of a kilowatt hour, the
basis on which bills for electric cur
rent are figured.
Such Is the conclusion from a study
Of lightning phenomena at the Blu
| reau of Standards, undertaken as a
basis for better protective devices. The
study delves into some OF the obscure
phases Of the behavior Of lightning,
such as the queer antics it plays when
1t strikes an object and the images 1t
sometimes leaves on human bodies,
| which have given rise to many pop
| ular SuperstitionS.
There is nothing mystical about
lightning, the report points out. al
though it occurs in so many forms.
and some of the factors are so obscure
that an entirely clear explanation is
impossible. Even the cause Is not GER
tainly known, but lightning generally
is believed to result from upward cur
rents of warm air meeting descend
ing water drops and breaking them
up into smaller drops, thus producing
electric charges which, after they
have accumulated for a time, are suf-
fcient to account for the electrical
effects in most violent storms.
Chains Are Visible.
A single flash is over so quickly that
the eye could not follow it. What actu-
ally Is seen are chains OF from three to
40 flashes with brief intervals between
them which the eye cannot grasp. This
accounts for the "hickering" sensation
which almost invariably follows a flash.
Thunder, the report explains, prob
ably is due to the heating and conse-
quent rapid expansion Of the atmos-
phere along the path Of q lightning
| flash. Thus a path through the air
about a foot in diameter and a mile
long, traversed by 100000, 900 watt
seconds Of electricity would be heated
to about $50 centigrade, and the ex-
pansion against the colder air outside
the path naturally would be accompa-
MED by an ear-splitting crash.
Why the lightning bolt is luminous
| Is not clear, since the actual heating
Of the atmosphere Of the path itself is
sufficient to cause only very faint
luminosity. The light probably Is due
to the ionization Of the air.
When persons are subjected to d.
rect lightning Strokes" says the report,
the result is nearly always fatal, al
though instances have been recorded of
extraordinary escapes from what seemed
to be direct strokes. The injuries in
f1icted consist of electric shocks of
greater or less severity which may be
combined with burns, and in some cases
tearing Of the flesh, apparently by an
explosive action Of the discharge. Burns
by lightning frequently assume fantastic
forms, and cases are reported where
images Of various kinds were i'm
printed on the body. That such burns
happen to be the image of anything
doubtless is matter of chance.
Influence on Images.
Their origin is probably in surface
discharges over the skin or in the LAYER
OF clothing damp with perspiration next
to it. This layer. especially in thunder
storm weather, affords considerable in
ducement to q discharge to follow it,
and the resulting heat, or burning by
ultraviolet rays, might cause almost
any Kind OF image to be imprinted.
First aid treatment for injuries by light
ming is the same as that for other cleo
trio shocks and burns. Artificial respi-
ration, II administered in time, doubtless
would prevent many deaths which result
from the fact that nine-tenths Of such
accidents occur in isolated places.
when insulating or sei11i-insuIatinr
material receives a discharge the dam
age Is usually severe and Of an explosive
character. Trees are frequently blown
TO Spl1nterS. Brick and stone work
sometimes are demolished locally and
pieces thrown 100 feet or more, Damage
seems to depend somewhat on whether
the material IS externally wet. Prior
10 rainfall the damage Is most extensive
ana afterward it becomes less. Trees
struck when thoroughly wet in MANY
Cases show only small piece of bark
stripped on here and there, the re-
mainder Of the path along the trunk
being barely traceable by slight SUPER
fetal damage, while trees struck when
dry externally are almost invariably
stripped or splintered from top to
"The cause Of damage of this sort
Is generally attributed to the forma-
tson OF steam at high temperatures
within pores OF the material, all por-
Gus material exposed to air being
known to contain more or less mois-
ture. It IS possible, however, that I'M
der the high current intensity Of a
lightning discharge some of the ma
terial itself is decomposed, with the
formation Of gaseous products such as
hydrogen, oxygen, hydrocarbons, ions
and electrons. When hydrogen
changes from the ionic state, as in
water, to the gaseous state at atmos-
pheric pressure, the volume occupied
at ordinary temperatures, increases
tube in wood filled with moisture at
ordinary pressure would be subjected
to an internal pressure greater than
1900 atmospheres. This would be
equivalent to- an explosion Of dyna-
mite and ample to account for the
explosive effects Of lightning. There
is also to be considered the electro
static repulsion between the electrons
traversing the pores, which may be