334 On Laghtning-Rods. 
a stratum of charcoal is then strewed over the bottom of the 
bricks, about two inches thick, on which the conductor is 
laid, and the trough is then filled with more charcoal, and closed 
by a row of bricks laid on the top. Iron, thus buried in 
charcoal, will suffer no change in thirty years. After leav- 
ing the trough, it is best to lead the conductor into a well, at 
least two feet below the lowest water mark. The extremity 
of the conductor should terminate in two or three branches, 
to afford a more re ady and divided passage to the lightning 
into the water. If there is no well convenient, then a hole, at 
least six inches in diameter, should be made, ten or fifteen 
feet deep, and the ia £98 sed to the bottom of it, in 
coal, and beat teeth as hard as ‘possible around the conduc- 
tor. In a dry soil or rock, the trench for the conductor shoul@ 
be at least twice as long as in a common soil, or even longer, 
if then it can reach moist ground. Should it be impossible to 
extend the trench, others, in a transverse direction, should be 
general, the trench should be made in the dampest, and 
consequently lowest spot near the building, and the water 
gutters made to discharge the water over it so as always to 
keep it moist. Too great precaution cannot be taken to 
ve the lightning a ready passage to the ground, for it is chiefly 
on this that the efficacy of the lizhtning-rod depends. 
ron bars being difficult to bend according to the projec- 
tions of a building, ithas been proposed to substitute metallic 
ropes. Fifteen iron wires are twisted together to form one 
strand, and four of these form a rope, about an inch in diam- 
eter. To prevent its rusting, each strand is well tarred sep- 
arately, and after they are twisted together, the whole rope is 
tarred over again with great care. Copper, or brass wire is, 
however, a better material for their construction than iron. 
Ifa building contain any large masses of metal. as sheets of 
detitak break in the forme “r, to die’ vay serious injury of the 
building, and danger of the inhabitants 
aft 
