Audubon County journal. (Exira, Iowa) 1884-1993, 1904-10-06


Been shattered-When n Bolt Strikes
Tree 1t Generates Steam From the
Sap and Explodes the Bark,
The explosive force of lightning act
ing on dead wood is not, as rule, so
great as when living trees are struck,
though Sir William Harris shows that
the masts of ships Of the line, three
feet in diameter and ITO feet long,
bound with hoops Of iron half an inch
thick and five inches wide, the whole
weighing about eighteen tons, have
been in many instances torn asunder
and the hoops of iron scattered about
the decks" 1t will be found, as rule,
that trees are struck by lightning far
more often than are buildings, even
if the trees and buildings are close to-
gether. This is partly because tn.
trees are higher.
But there must probably be some I'M
known reason not only for the fire.
quency with which trees are struck,
but for the recurrence of such shocks
in the case of particular trees or trees
in the same locality. The commonest
form of injury is that the current
passes down the bark of the tree. strip
ping off the band, wider or narrower,
from top to bottom. Sometimes on an
oak two or three of these lightning
marks are seen, evidently caused at
different times.
There must be something in the form
0r ci}, or%h {ho
which endangers it. An instance is
quoted in Mr.. Anderson's descriptive
book Of the Church Of st. Mary in
Genoa, which was frequently struck
by lightning, sometimes as often as
twice year. 1t was noticed that the
electric force always followed the same
track. 1t was discovered later thai
the walls were clamped with iron, ana
that the lightning had followed the
patch in which the metal offered the
greatest continuity, destroying the zone
between.
If the ground below the tree or build
ing is hard and dry, the contact with
the earth, in which the lightning ex-
pands its force and disperses, is diff
cult, and the destruction of the object
struck is likely to result. This may
explain the frequency with which
BLASTED" tree is seen extending its
dead arms on the summit of some rocky
cliff or peak. The ground below it is
dry and does not easily lead away the
current into the earth.
At the same time thunderclouds I'M
doubtedly tend to discharge, or perhaps
it would be safer to say that the trans
mission from the cloud to the earth
more frequently takes place, near
pieces of water and along the courses
of rivers than elsewhere.
In park in one of the eastern coun.
ties of England there is large lake.
The park contains more trees struck by
lightning than the whole Of the rest Of
the estate. Some miles away is road
called locally the lightning road"
from the frequency with which acct
dents have occurred there either to
trees, horses. cattle or passengers. In
this park there recently occurred an in
stance Of the explosive effect in GER
tain circumstances not perfectly known.
very tall spruce, probably 100 feet
tom into pieces the size of the wood
used in making chairs. Every shred Of
bark was stripped from them, and the
wood looked as if it had been shredded
up for firing. A similar instance oc-
Cured some years ago when an oak in
the grove below the foot of the White
lodge in Richmond park exploded I'M
der lightning shock The bark flew off
and simply disappeared in small patch
es, and the rest of the tree was shat
tered into white fragments.
In these cases it is probable that the
current sets up such tremendous heat
that all the sap in the tree is converted
into superheated steam, which eX-
pfodes. The greater the heat the more Of
the cells in which moisture lies are ex-
ploded and the greater the destruction
of the tissues of the tree. AS there is
most moisture between the bark and
the trunk the first and greatest explo-
sion takes place there, instantly driv-
ing the bark away into space. Ere
Quently the explosion only takes place
at that point.
AS Sir Hiram Maxim pointed out
after the great explosion of Mont
Pelee, very similar method is now
used by the American manufacturers
Of wood pulp. The logs Of fir are
placed in strong chamber, and there
subjected to the action Of superheated
steam until the water in every cell is
converted into explosive gas. The
chamber is then opened and the log
explodes, converting itself into wood
powder.-London Spectator.
Egyptian Weather.