334 On ILightning-Rods, 



a stratum of charcoal is then strewed over the bottom oi 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 i^ best to lead tht- 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 ready and divided passage to the lightning 

 into the water. If there is uo well convenient, then a hole, at 

 least six inches in diameter, should be made, ten or fifteen 

 feet deep, and the conductor pat-sed to the bottom of it, in 

 the centre, and the hole then carefully filled up with char- 

 coal, and beat down as hard as possible around the conduc- 

 tor. In a dry soil or rock, the trench for the conductor should 

 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 

 made, in which are to be placed small bars of iron, surround- 

 ed with charcoal, and connected with the conductor. In 

 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 

 give the lightning a ready passage to the ground, for it is chiefiy 

 on this that the efficacy of the lightning-rod depends. 



Iron bars being difficult to bend according to the projec- 

 tions of a building, it has 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. 

 If a building contain any large masses of metal, as sheets of 

 copper or lead on the roof, metal pipes and gutters, iron 

 braces, &,c. they must all be connected with the lightning 

 rod, by bars of something less than half an inch square. With- 

 out this precaution, the lightning mi^ht strike from the con- 

 ductor to the metal, especially if there should be any acci- 

 dental break in the former, to the very serious injury of the 

 building, and danger of the inhabitants. 



