322 IMPROVEMENT on 
quent inftances of thefe conductors having their tops melt- 
ed off by a ftroke of lightening, it appears that this admi- 
rable contrivance for guarding houfes againft the danger- 
ous effects of lightning is, in fome degree, ftill imperfect. 
Some improvement feems yet to be wanting at both ex- 
tremities of the rod—at the upper extremity, to fecure it 
againft the accident of being melted, which renders it af- 
terwards unfit to anfwer its original intention, viz. draw- 
ing off the eleétric fluid, or lightening, from the pafling 
cloud, in a filent, imperceptible manner; for it is only 
pointed condutors that poflefs this property—and at the 
lower extremity, to afford a more ready paflage for the 
fluid into the furrounding earth. 
The firft of thefe intentions, would, I am perfuaded, be 
effectually anfwered, by inferting in the top of the rod a 
piece of black-lead, of about two inches long, taken out of 
2 good pencil, and terminating in a fine point, pro= 
jecting but a very little above the end of its metalic 
focket; fo that, if the black-lead point fhould happen to 
be broken off by any accident, of which however | think 
there can be but little danger, ftill the point of the rod would 
be left fharp enough to anfwer the purpofe of a metalic 
condudtor. 
This fubftance 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, im his mineralo- 
gy fet. 231, except ina 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 conductor of electricity 
is perhaps equal, or but little inferior, to that of any of 
the metals. A line drawn on a piece of paper, by 
a black-lead pencil will, as I.have often experienced, con= 
duct an eleQtric explofion feemingly as well as a fimiliar 
line 
