LIGHTNING. 
at the fummit. It would feem as if the lightning had 
met with obftacles, and that it had not the fame force 
when it attacked the higher parts of the tree. In my 
opinion the thunder which produced thefe effects was all 
afcending; and I often obferved holes at the roots of the 
trees which had been deprived of their bark. I obferved 
alfo that dry land had been lefs flruck with the lightning 
than moift land, which induces me to believe that the 
greater part of the thunder that year was afcending.” 
Thefe particulars are collected from the third and fifth 
volumes of the Philofophical Magazine. 
Conductors of lightning are pointed metallic rods fixed to 
the upper parts of buildings, to fecure them from ftrokes 
of lightning. Thefe were invented and propofed by Dr. 
Franklin for this purpofe, foon after the identity of elec¬ 
tricity and lightning was afcertained ; and they exhibit a 
very important and ufeful application of modern difco- 
veries in this fcience. This ingenious philofopher, hav¬ 
ing found that pointed bodies are better fitted for receiv¬ 
ing and throwing off the electric fire than fuch as are 
terminated by blunt ends or flat furfaces, and that metals 
are the readielt and bed conductors, foon difcovered that 
lightning and electricity refembled each other in this and 
other diltinguifhing properties ; he therefore recommended 
a pointed metalline rod to be raifed fome feet above the 
higheft part of a building, and to be continued down into 
the ground, or the nearelt water. The lightning, fhould 
it ever come within a certain diltance of this rod or wire, 
would be attracted by it, and pal's through it preferably 
to any other part of the building, and be conveyed into 
the earth or water, and there diflipated, without doing 
any damage to the building. See the article Electricity. 
Many faCts have occurred to evince the utility of this Am¬ 
ple and feemingly-trifling apparatus. And yet fome elec¬ 
tricians, of whom Mr. Wilfon was the chief, have ob¬ 
jected to the pointed termination of this conductor; pre¬ 
ferring rather a blunt end ; becaufe, they pretend, a point 
invites the eleCtricity from the clouds, and attracts it at 
a greater diltance than a blunt conductor. This fubjeCt 
lias indeed been very accurately examined and difcufled ; 
and pointed conductors are almolt univerfally, and for the 
bell reafons, recommended as the molt proper and eligi¬ 
ble. A lharp-pointed conductor, as it attracts the elec¬ 
tric fire of a,cloud at a greater diltance than the other, 
draws it ofi' gradually ; and, by conveying it away gently, 
and in a continued ftream, prevents an accumulation and 
a Itroke ; whereas a conductor with a blunt termination 
receives the whole difcharge of a cloud at once, and is 
much more likely to be exploded, whenever a cloud comes 
within a ftriking-diltance. To this may be added expe¬ 
rience; for buildings guarded by either natural or artifi¬ 
cial conductors terminating in a point, have very feldom 
been (truck by lightning; but others, having flat or 
blunt terminations, have often been (truck and damaged 
by it. 
The belt conductor for this purpofe (fays Mr. Cavallo) 
is a rod of iron, or rather of copper, as being a better 
conductor of electricity, and lefs liable to ruft, about three 
quarters of an inch thick, which is either to be fattened 
to the walls of a building by wooden cramps, or fup- 
ported by wooden pofts, at the diltance of a foot or two 
from the wall; though lefs may do; the upper end of it 
lhould terminate in a pyramidal form, with a (harp point 
and edges ; and, when made of iron, gilt or painted near 
the top, or elfe pointed with copper; and be elevated five 
or fix feet above the higheft part of the building, or 
chimneys, to which it may be fattened. The lower end 
fhould be driven five or fix feet into the ground, and di¬ 
rected away from the foundations of the building, or con¬ 
tinued till it communicates with the neareft water; and, 
if this part be made of lead, it will be lefs apt to decay. 
When the conductor is formed of different pieces of me¬ 
tal, care fliould be taken that they are u'ell joined ; and it 
is farther recommended, that a communication be made 
from the conductor by plates of lead, eight or ten inches 
C<J5 
broad, with the lead on the ridges and gutters, and with 
the pipes that carry down the rain-water, which fliould 
be continued to the bottom of the building, and be made 
to communicate either with water or moift earth, or with 
the main pipe which ferves the houfe with water. If the 
building be large, two, three, or more, conductors fliould 
be applied to different parts of it, in proportion to its 
extent. 
Chains have been ufed as conductors for preferving 
(hips ; but, as the eleCtric matter does not pals readily 
through the links of it, copper wires, a little thicker than 
a goofe-quill, have been preferred, and are now generally 
ufed. They fhould reach two or three feet above the 
higheft matt, and be continued down in any convenient 
direction, fo as always to touch the fea-water. 
Mr. B. Cook, after Hating the frequency of the ac¬ 
counts publilhed of damages caufed by lightning, re¬ 
commends the ereCtion of conductors all over the king¬ 
dom, at the diftance of five or fix miles ; the expenfe of 
which, he thinks, would be faved in a few years, from 
the mifchief they would prevent; and propofes that every 
parifh fliould ereCt four or fix conductors, according to 
its fize, as a mode of putting the above plan into execu¬ 
tion. 
Mr. Cook next dates the great imperfection of iron 
conductors, arifing from their liability to ruft, the irre¬ 
gularity of their furfaces, which tends to caule the elec¬ 
tric fluid to fly off to any other conducting fubftance near 
them, and their not being raifed to a fufficient height 
above the buildings which they are intended to protect, 
and which height fhould at leaft extend to fix or eight 
feet. From the fcale given in our article Electricity, 
vol. vi. p. 426. it appears, that gold and filver are the beft 
conductors, copper and brafs the next, and iron, &c. the 
worit. Mr. Cook therefore propofes to ufe brals for this 
purpofe ; and, in order that it may be obtained fuffici- 
ently cheap, and of the proper degree of fmoothnefs, re¬ 
commends that it be ufed in the form of coating to iron 
tubes, and patted through pclifhed draw-plates : for per¬ 
forming which operation in a manner that unites the brafs 
fo perfectly to the iron, by compreflion, as to appear but 
one piece, and fo as to form a coating of one-fixteenth cf 
an inch in thicknefs, Mr. Cook has difcovered a very ef¬ 
fectual method, for which he has obtained a patent. 
Inftead of brafs, Mr. Robert Patterfon, of Philadelphia, 
propofes to fix upon the top of the iron rod a piece of 
black-lead , of about two inches long, taken out of a good 
pencil, and terminating in a fine point, projecting but a 
very little above the end of its metallic focket; fo that, 
if the black-lead point fhould happen to be broken off by' 
any accident, Hill the point of the rod would be left 
(harp enough to anfwer the purpofe of a metallic con¬ 
ductor. “ This fubftance (Mr. P. obferves) is well-known 
to be infufible by the greateft heat, and hence its ufe in 
making crucibles; nor is it evaporable, as remarked by 
Cronftedt in his Mineralogy, except in a flow calcining 
heat, to which it could never be expofed on the top of a 
lightning-rod. At the fame time its power, as a con¬ 
ductor of eleCtricity, is perhaps equal, or but little infe¬ 
rior, to that of any of the metals. A line drawn on a 
piece of paper by a black-lead pencil will, as I have of¬ 
ten experienced, conduct an eieCtric explofion feerningfy 
as well as a fimilar line of gilding would do; and that 
without ever lofing its conducting power, which is not 
the cafe with gilding.” 
Mr. Patterfon then propofes an improvement in the 
mode of directing the efcape of the electric fluid from 
the lower part of the rod into the furrounding earth. “ It 
is in many cafes impracticable, from the interruption of 
rocks, or other obftacles, to fink the rod fo deep as to 
reach moift earth, or any other fubftance which is a tole¬ 
rably good conductor of eleCtricity. Nor, even if this 
were praiticable, would it, I prefume, beplone fufficient 
to anfwer the defired intention. Iren buried in the earth, 
and efpecially in mcift earth, will prefently contract a 
1 ‘ coat , 
