The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1899-12-31
OZARK LIGHTNING. i"
A Puzzling Phenomenon Explained
By Professor Wood.
New York Tribune.)

(New York Tribune.)
A mystery in regard to lightning
flashes has at last been cleared up
Within the last few years large num-
Der of photographs have been taken in
which the path of the thunderbolt APP
peared as dark line instead of a bright
one. The curiously meandering route
of the line. as well as its characteristic
,, ramifications, proved Enthusiastically
that it represented lightning.
One suspicion that has been enter
tanned is that the intensity of the light
produced what is called, a reversal
on the Photographic plate. 1t is a we'll
established fact that if an attempt is
made to photograph the sun, or a
small part of the solar surface, the
image obtained will be black and not
white, If the time of exposure is not
very brief. Photographers have been
greatly bothered to abbreviate the ex-
posture sufficiently to get proper pic
ture of the sun. 1t was observed. how
ever. that faint lightning flashes came
out dark in photograph as well as
bright ones. and thus it was proved
that intensity was not the true ex-
PLANTATION of, the puzzling phenomenon.
The appearance of dark and bright
flashes on the same plate led to little
speculation as to the possibility of
there being two kinds of lightning. a
dark kind and a bright. But no expert
in electricity could be found who would
sanction such notion, and it was i'm
possible to obtain any evidence of such
flashes actually having been seen by
anybody. Indeed it is hard to conceive
of such thing as a dark flash.
Professor R. W. Wood of Madison,
Wis, has ascertained that the brevity
of lightning flash has something to
do with the observed effect. He tried
a number of laboratory experiments
like those of Mr.. Lockyer. but tried
other means of illumination than the
spark. The whole of a sensitive plate
was exposed to candle light for a sec
ond or two, and then a portion of it was
exposed again. 1t was then found that
the doubly exposed part was affected
twice as much as the rest of the plate.
There was no reversal here. A much
more rapid flash was then tried. An
explosion of oxygen and hydrogen gases
was brought about. twice in succession,
and the same plate exposed to both
flashes. These flashes s last about
1-12.0e0 Of a second. But Professor
Wood failed to get reversal. and thus
was led to conclude that the time was
too long. Finally he arranged a mech
dIiSfll WHICH fNOulQ dllOW d Dcdlu VI
light from an electric arc to pass
through a slit that was opened for only
$4,000 of second. Then he was able
to reproduce the phenomenon of re-
versal every time. The brevity of the
flash. then. seems to- be another factor
in the case. iadr. 4dl
The mystery is thus found to be a
chemical one. 1t resides not in the sky,
but in the sensitive film on the photo
graphic plate. There is no such thing
as dark lightning. What actually hap
pens is this: The sensitizing materials
are paralyZed- 80 to speak, or rendered
almost entirely imperative, where the
image of the flash falls upon the plate.
The rest of the plate may then regis
ter later flashes. and even stationary
objects, like buildings, but no such ac-
ton can occur ralQfls, the, insensitive
streak made by the final flash.
Mr.. Lockyer has suggested that in
the thunderstorm season amateurs ar
range to expose two cameras side by
side, directing them to the same quar-
ter of the heavens. Then. after a par
ticularly bright flash. one instrument
should be capped Immediately while
the plate in the other should be kept
exposed long enough to record one or
two more flashes. IL anyone can get a
dark flash for his first and only image
he. will upset Mr.. Cfayden's theory. but
until someone does so that hypothesis
will probably be generally accepted.