The Sauk Centre herald. (Sauk Centre, Stearns County, Minn.) 1886-current, 1888-05-17
LIGHTNING STRIKES
TO RELIEVE THE ELECTRICAL TEN
SION OF THE ATMOSPHERE.

SION OF THE ATMOSPHERE.
The Mysterious, Unexpected and Fro.
quently Fatal "Return Stroke"-where
tho Flash Takes Place and why-Con.
Quoting Currents-High Houses.
Now, as a charge of electricity has the
property of inducing another charge of
electricity of an opposite kind to itself on
any conducting" matter near it, and as
the earth is composed of what is called
conducting matter, it follows that
charged cloud sailing over the surface of
The earth induces an opposite charge on
the ground below. These two opposite
charges, one of positive" the other of
negative" electricity, tend, by another
well known property Of electricity, to rush
toward each other and combine. Hence
when they are able to overcome the resist
ance of the air between, which keeps
them apart, they leap together with flash
and crack, producing the familiar phe-
nomena of thunder and lightning.
Sometimes another cloud floating near
the first one takes the place of the earth,
and then the lightning fash takes place
between them. Lightning of this kind
have o destructive effect on the latter for
all that, because it might give rise to the
''back stroke, which u sometimes fatal
20 life. The ''back stroke" Is not dse to
the direct flash and discharge. It y
rather the reaction after the direct dis
charge hs saken place elsewhere. Sup
pose, Tor example, that track Of upland
co J, rural district with trees, farms,
and here and there church dotting it, is
covered by thunder cloud, which induces
q charge of electricity upon it. In order
that the charge upon the earth may get
nearer to that upon the cloud, 50 as to
combine with it, the electricity, by another
well known property, viii heap itself on
the most prominent and pointed objects Of
the landscape. That is to say, it will &C
cumulate on the trees, barns, chimney
tops and spires Of the district.
The whole atmosphere Of the region IL
in state Of tension and suspense. The
bolt Is trembling in the balance, but no
there Il binding flash Of light, tho sky
stantly the tension is relieved. The dis
charge has taken place at ono point, the
point which offers the path of least resist
electric tension was most critical. At
every other place where the electricity
had seriously accumulated, there is con-
sequently a sudden fall of electric poten-
tial, or a collapse to its old condition, or,
as it is called, ''return stroke" This
instantaneous change Is sometimes as
fatal rs the direct discharge, and it may
ruin a building or destroy life several
miles from the scene Of the flash. The
return stroke is therefore more mysterious
and unexpected than the flash, but fatal
effects are comparatively rare from It.
Nevertheless, since the latter have been
attributed to this cause, person cannot
feel quite safe, although a thunder storm
with lightning is still several miles from
him; the number of miles being estimated
by counting the seconds which elapse be-
tween the flash and the peal, and allow
ing q distance of four miles for every
second counted. He may feel safer than
if it were close upon him, but there is still
some room for fear.
In fact there is no real safety except
within the area properly protected by
lightning conductor, Or in a building
which is itself protector, for instance a
sheet iron house. Every building, then,
should be protected in order to be safe.
In the country, where these are often
isolated, a lightning rod would be required
for each; brit in towns one rod would
sometimes pi >ect more than one house
around it, accol ling to its height and con-
ductivity.
The flash takes place at the point of
least resistance, because it is here that the
two opposite electricitics can easiest rush
together. But the cagcrness with which
they tend to rush together is another
thing to be considered. These two things
taken together determine the discharge.
There may be less resistance to the flash
at one house or tree than at another, but
if the attraction between the opposite
electricities is less at the former, the flash
may traverse the latter house. Hence
ono cannot exactly say if one tree or
1Ldllding will be safer than another. There
is great uncertainty, and this is a reason
for tLs instinct Of awe and uneasiness
which most animals feel on the approach
Of thunder storm.
In general, however, we can say that
high houses, or those perched ON high
ground, are more likely to suffer from the
discharge than small low lying houses.
The former are therefore all the more ELI
gible for protection; and they are to be
avoided in seeking shelter from a storm.
so are houses surrounded by trees, and
with ponds or pools of water close beside
them. For trees act as imperfect light
ming rods, having good earth connection,
and especially if they are wet the dis
charge may strike the house in order to
reach the ground through them, or, in the
case of the pond, through the water. One
should not shelter under trees of any
kind, but more especially tall, soft trees
like poplars. Many deaths have been in
Cured from sheltering under poplar trees
in France.
Thunder storms are said to be more
in open, treeless countries, such
as the Transvaal or the Scottish hills, and
the fact has been attributed to the I'M
checked ascent of electrical vapors; but
on the other hand they are probably less
destructive in such countries.
Chimneys, by creating currents of warm
Smoke and by their lining of conducting
SCOT, are dangerous parts of houses, and
there are many instances of the discharge
taking that road. It were better, then, to
avoid sitting near fire in a storm. In
deed, the safest place in the house on such
an occasion would seem to be in the cellar
and basement rooms or upon an iron bed
stead. In the open air there cannot be a
safer place than a dry hole or ditch, for it
places the body below the surface of the
ground, and therefore not exposed on a
prominent place. But it should be q dry
hollow, else the water in it may invite the
discharge; for water, being conductor in
good connection with the earth, lowers
tie resistance to the discharge. -Engineer-
ing
Brazil's Diamond Mines.
A gentleman who returned from the
diamond districts of Brazil recently says
that the stories OF exhaustion of these
once profitable mines are pure fabrica-