, 1870-09-08
L1RhtnluK-Rods.

... . NkH YORK, Sept 4, lSs0.
1a the Editor AZ 1A< c2tedgo Tt1oune:
I have seen in late number Of TEE Ca1oA-
90 TRIBUNE letter on lightning-sods, by G.
Wright, 'of Rock Falls, Ill. Some >of Mr..
Wright's ideas arc correct, hut his statements
are not, all: Of them, veil considered Tbs
earth conducts in proportion to tho presence
within it Of superior condu ctors, such as me-
tallic ores or water. Wet earth ia better
conductor Of electricity than dry earth, aud
body Of wAter is Il better conductor than
either. Tha difference between the cunduct-
ing power Of water and. tbs metals Is as unity
to millions. Tha relative differences between
different metals is, therefore, unworthy Of
lightning-rod- The essential point is TO
contrive a substantial and durable rod, md to
so arrange it upon the, building sought to be
protected AZ to provide beforehand for MI the
contingencies OF exposure to lightning which
can tossibly arise. For example, We might
north end Of building, letting it 60 down to
thoroughly and permanently moist earth, and
get discharge Of lightning tending to PASS
obliGuely from u cloud north OF the building
to come point eouth Of it might, although rc-
celved upon the rod, ieaye the rod aud so
tination, ia preference to passing down the
rod to the ground and goiug through the
ground in horizontal direction underneath
the building; whereas, il we should hara
rod upon the south end OF the building, con-
nected by rod acrpss the root with the rod
On tue north end, auch u discharge would 20
across on tho roof rod, aud down u the earth
by tbs south rod, In word, lightning-rcds,
to be efficient under all circumstances, must
te so located Or arranged upon the building
that. from whatever quarter the discharge
may come, Or in whateveI direction it tends
tF1Y he'll t&Y111 HrETtk
ning-rod continuous line ot conducting mat
ter superior to anything within the building.
It must be remembered that d discharge Of
lightning does mol move At random, but al
wsys has fixed destination, and invariably
takes the path Of least resistance to reach
that destination.
1t has bean my buriness al my life to study
bui11ings with reference to determining tho
raturo and degree OF their exposure Rs re-
CARDS lightning, and to prescribe such guam
fity and arrangement Of 1ightnlng.roda hs
would III my Judgment meet the requirements
any instance failed to afford complete pro
lection from lightning to the buildings upon
which they hare been pfaced.
Mr. Wright under-estimatea-the cost of pro-
tectiug premises like the Pittsburgh Oil Works.
Oh works are commonly enyclopcd in the va
por Of petroleum which rises to cons.derA-
hle height, and which the 1eist spark will iu-
fame Such promises therefore need Light
| ing rods elevated On u3Asts sufficiently high to
project above tl,is inAa1n1nnhlc vzpor, and Of an
especial construction II to continuity which il
not necdfu1 upon any other class OF buildings.
Al masses OF metal above them snch as
tanks, boilers, and pipes must bo carefully
| connected with each other, and with the light
| uing-rod, 60 that there sha1l be no possibility
| OF the slightest spark of electricity nnywhczc
| on the premises, owing to break IN continuity
from one mass Of metal to onother.
| EpwARD E. Quincy.