The Elk Mountain pilot., 1899-11-07
Protection from Lightning.

A monograph on Lightning and the
Electricity of the Air." recently is
sued by the United States Weather
bureau, affords some interesting in
formation upon the question of pro-
tecting buildings from lightning, To
what extent is it practicable to pro-
tect building and to what extent is
it profitable to attempt such protection
when it is practicable? Before an
swering these questions 1t is necessary
to convey clear idea of the nature of
the lightning flash. The old idea is
that the flash, like the moderate cur
rent of electricity with which we are
familiar, follows the line of least re-
sistance, and can be diverted by con-
ductor of a certain size. In this view
the lightning-rod is like a channel
made to convey flow of water, and a
small channel will empty large reser-
voir II given time enough. But the
Weather Bureau likens the lightning
flash rather to an avalanche, a land
slide down the side of a mountain or
the breaking of dam-the whole
force is exerted in one instant and
there is no after current. The flashes,
of them being mild affairs. And it is
always true that well-constructed
and well-arranged lightning-rod viii.
if given time, silently convey away
vast deal of electricity, thus lesseninG
greatly, if not preventing, the ultimate
flash. 1t is on this account that light
ming strokes are comparatively infre-
quent in large cities. where lofty spires
and roofs drain overcharged clouds be-
fore the stratum of air between the
cloud and the houses is strained to the
breaking point. 1t follows from the
avalanche-like nature of lightning that
absolute protection of building Is
impracticable unless the building it
self-as being steel structure-is
itself a good conductor. But a very
large measure of profession is within
our reach. A chimney or church spire
well provided with rods is almost per-
fectly protected and rods distributed to
exposed points will reduce the risks of
a wide roof area as much as seventy
five per cent. There is no definite
"area of protection" The old rule was
that rod protects radius equal to its
height, and the rule may stand for
want OF a DetleT DuI as d HdtteT VI
fact it holds good only with electrical
discharges of moderate volume.
Whether it pays in particular case
to invest money in lightning de-
pends upon circumstances. Sometimes
the risk is SO slight as to be neglected.
The cost of the rods may be such as to
render fire insurance preferable. But
where the risk of being struck is very
great-as in case of church spires and
high brick chimneys-the value of the
property threatened renders the light
ning-rod necessity. 1t may be said
to be necessary also where the risk is
less, as, for example, for buildings that
contain great number of persons
large summer ahotels, large school
buildings, asylums and expensive pub
lie buildings. A very costly building
cannot be wisely subjected to a slight
risk from lightning If protection can
be obtained The risk on farm build
ings is greater than on any other class
OF buildings, but where their value is
email it is usually preferable to rely
on insurance for protection. AS to the
nature of the rod, it is stated that
either iron or copper may be used. and
iron=isa good as copper. provided the