Evening star., 1933-05-28

in glass tumbIerS and roost cotrering on
this supposedly insulated perch during
O. thunderstorm.
not the geometrically regular series of angles
in which the older artists seemed to dehght
1t is as crooked as the course of a brook, or
the root of tree. Indeed, branching streaks
of lightning do bear a most startling resem-
bance to root systems, sometimes, as you have
perhaps noticed for yourself.
Lightning does not always leap from the
cloud to the earth. Many, probably most,
lightning discharges occur between cloud and
cloud, or even between the top and the bottom
of the same cloud.
A horizontal cloud-to-cloud lightning stroke
may travel as much 20 miles. Vertical
flashes from cloud to earth, are seldom as
much as mile in length.
While lightning will occasionally strike the
level earth, usually its target is some projecting
object-a house, or a tree, or transmission
line tower. This is because the path-preparing
brush discharge is more likely to start from
projection than from level surface.
BY that rule, therefore, The neighborhood OF
anything prominently projecting is danger
Gus during a thunderstorm. 1t is a great
temptation to take shelter from the pelting rain
under big tree but that is the thing most
likely to draw lightning
II you are in the woods keep away from the
tall trees and near the the low ones, when the
storm breaks. If you are in the fields, and
lightning begins to pelt the earth around you.
lie down. Then you'll have as much chance
at least as the worms and toads and other
humble things
If you stand up proudly and assert yourself
like Ajax, you're offering nice little projec-
tion for the start of of these lightning
coaxers, a brush discharge. Ajax may have
appealed to Homer, but to a modern meteorolo-
gist he was just darn fool tang an awful
chance. He got away with it, so he lives in
literature as a hero-abeit a stupid one.
Indoors, you are safest in steel-frame build
ing if the frame is well grounded. Next to
that, in safety, is any kind of building really
thoroughly equipped with lightning rods. But
most protected" buildings don't have the job
done half well enough.
- A CCORDING to Prof. w. J. Humphreys of
the United States Weather Bureau there
should be a rod, preferably feet high on
every chimney, gable end and other projec-
ton. The conductors should be solidly con-
nected with each other and with all plumbing
and piping in the house, and should finally be
grounded deep in perpetually moist earth.
This sort of an arrangement he says, will
not insure against all damage, but it will make
house much safer than one with no rods or
with rods carelessly or inadequately installed.
How small a fraction of a second a flash
of lightning lasts was for long an unSoved
riddle. However, several methods of getting
an estimate, most of them involving the use
of special cameras, have been used with appar-
emily satisfactory results.
Possibly the closest measurement of lightning
time was made by DR.. c. v. Boys, noted Eng
hsh physicist, during visit to America some
time ago. His calculations of one flash he
caught with camera fitted with two revolv-
ing lenses indicate total travel time for the
flash of one seven-thousandth of second. So
quick as flash" is really pretty quick.
What causes the binding white light OF
lightning is still pretty much an unsolved
riddle. It can hardly be entirely due to the
heating Of the air, Prof. Humphreys thinks.
More likely, he suggests, it is an atomic 'ex-
citation" phenomenon, similar to what we see
in the glowing neon-tube signs in the streets.
The cause of thunder is most plausibly ex-
planned by the sudden expansion of the atmoS-
phere along the course of the fash, due to the
brief but intense heat. 1t is in the same cate
CORY as the sound Of big gun, but it lasts
longer because the sound takes some time to
travel to us from the more remote parts OF the
flash; and the effect is aggravated by the
1lraJr,a cafsf tic vSotI