Wausau pilot. [volume] (Wausau, Wis.) 1896-1940, 1907-07-30
STUDIES OF LIGHTNING.
INTERESTING FACTS LEARNED
THROUGH PHOTOGRAPHY.

With the Aid of Grant From the
Smithsonian Institution-Minor vi
brations Of the Lightning Flash
Invisible, or Black. Lightning.
Three years ago, relates the Wash
ington correspondent of the New York
Evening Post, the Smithsonian Insti.
tuition received letter of inquiry.
Framed in a foreign hand upon scrap
of paper and expressed in quaint Eng
nsh. ii incidentally mentioned some
curious experiments which the author
had made in odd moments. With a
small camera which he held in his
hand, and revolNed from side to side,
he had taken some photographs of
lightning. He enclosed a print in his
letter, and wanted to know whether
his results had any scientific value.
The idea of photographing lightning
with a moving camera was novel
one to the Smithsonian experts, and.
after an investigation, these officials
decided that such experiments We're
worthy of assistance. A grant was
therefore voluntarily made to enable
the continuance of this photographing
with more accurate apparatus
In letters which followed it was
learned that Alexander Larsen, for
such was the writer's name, was a
Danish immigrant, educated in phys
les, chemistry, and electrical engineer.
ing at night school, and that all his
experiments were performed for the
pure enjoyment of doing something
new. With the aid of the Smithsonian
grant Mr.. Larsen constructed special
apparatus for his work. Upon a re-
volving table turned by timed motor
were placed cameras In such a posi-
ton that they would not miss fash
when one occurred. To secure the
photographs desired, the tabletop was
then revolved at certain speed.
The results are interesting. Where
the fash appeared perpendicular. the
negatives show a broad sheet for a
mere streak of lightning. BY calculat-
ing from the speed of the cameras
motion and measuring the width of the
sheet, the time of the flash is determ-
Unable. But the photographs showed
at the start that a single flash is not
one big vibration. 1t is made up OF
many minor flashes, or rushes, follow
ing usually in the same channel as
the first, and herein lies the special
value of the work. In the best of the
negatives, there are easily counted as
many rs forty separate rushes which,
as the whole flash lasted little over
half second, followed each other in
marvellously rapid succession. BY
measurements and by subsequent cal
culatSonS, Mr.. Larsen determined the
actual time between each rush. The
figures, as may be imagined, are al
most inconceivably small, varying
from the largest, three one-hundredths
of a second to the smallest, as low as
two one-thousandths of a second.
There appear many peculiarities OF
these separate rushes which might
bear scientific investigation, but the
most salient feature over which mete-
biologists and electrical engineers may
puzzle is recorded on some of the
plates, among all the bright oscilla-
tions. as a marked black rush of light
ming. The idea of lightning produc-
ing the extreme darkness is repugnant
to the name of lightning" Yet the
black rush is plainly visible. Mr.. Lar
sen, after refuting number of sug-
gestions that might be made to ac-
count for it, ventures his own theory
to solve the puzzle. I'm discussing the
record of a particular flash in which
the mark of the black rush is very
distinct, he concludes:
1.-THE flash must have given out light
of a wave length much shorter than
the wave lengths of visible light and
with a power sufficient to render the
part of the plate struck by it nom
sensitive to ordinary light. Such a
flash world appear black on par
TALLY Illuminated background, or be
invisible"
Invisible lightning" therefore,
seems to be a term perfectly proper,
in view of the results recorded in
some of these photographs.
At the suggestion of the institution
officials, and with their help, Mr.. Lar
sen carried his researches still further
into the actual makeup of lightning.
Photographs and studies of the light
spectra OF electric flashes in the air
were compared with sparks produced
by a static machine. The conclusions,
in line with the century-old observa-
tons of Benjamin Franklin, show that
there is little perceptible difference.
But Mr.. Larsen's spare time is not
spent entirely in waiting for thunder
storms He has been interested also
in studying the colored-light waves
given off by many kinds of substances,
minerals and chemicals, solid and
liquid, and gases, when they are them
selves subjected to light action. This
is known among men of science as
the f1Gorescence of substance, and
speaking in popular terms is not very
different from phosphorescence. In
these Investigations he has been as
sisted directly by the National Mu
scum, which has advised him and loan
ed him hundreds of specimens of geo.
ology. The results which he has for
warded, say the museum experts, are
vitality interesting to the student Of
this particular property Of matter.
The latest ideas outlined by Mr.
Larsen to the Smithsonian Institution
are no less remarkable than the first
He proposes to photograph electric
sparks reflected in a rapidly revolving
mirror, and thereby secure records.
study of which may add materially to
our knowledge of electric action. His
Investigation of huorescence. too. he
intGds to carry into greater detail
by passing an electric current through
substances in vacuum, and watching
the results.