LIGHTNIN G-RODS. 323 
Kine of gilding would do, and that without ever loofing 
its conduting power, which is not the cafe with gilding. 
The fecond intention is, to facilitate the efcape of the 
electric fluid, from the lower part of the rod into the fur- 
rounding 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 tolerably good conductor of ele@ricity. Nor 
even if this were practicable, would it, I prefume, be 
alone fufficient to anfwer the defired intention. Iron, 
buried in the earth, and efpecially in moift earth, will 
prefently contract a coat of, ruft, which will continually 
increafe till the whole is converted into ruft: but ruft of 
iron, and indeed the calx of all metals, is a non-conducfor, 
or at moft but a very imperfe& conduétor of the electric 
fluid. Hence itis eafy to fee, thatin afew years after a 
lightening rod has been erected, that part of it which is 
under ground will contribute little or nothing towards the 
fafety of the building. Befides, the furface of this part of 
the rod is too fmall to afford an eafy and copious difcharge 
of the electric fluid into the furrounding earth, when this 
is but an imperfe& conductor. 
Asa remedy for thefe defects, I would propofe, that 
the part of the rod under ground be made of tin, or 
copper, which are far lefs liable to corrofion or ruft, by 
lying under ground thaniron. Or, which perhaps would 
an{wer the purpofe better, let this part of the rod, of what- 
ever metal it be made, be coated over with a thick cruft of 
black-lead, previoufly formed into the confifience of pafte, 
by being pulverized and mixed with melted fulphur (as in 
the manufa@tury of the ordinary kind of black-lead pen- 
cils) and then applied to the rod while hot. By this means, 
the lower part of the rod would, I apprehend, retain its 
conducting powers for ages, without any diminution. 
Ss 2 Tn 
