On Lightning-Rods. 333 
by lightning. A lightning-rod, therefore, need not be of a 
greater size ; but as its stem should rise from 15 to 30 feet 
above the building, it would not be of sufficient strength at 
the base to resist the action of the wind, unless it were thick- 
er at that end. An iron bar, about 2 of an inch, is sufficient 
for the conductor of a lightuing-rod. 
A lightning-rod consists of two parts, the stem which 
jects above the roof into the air, and the conductor via 
descends from the stem to the ground. The stem is pro- 
posed by M. Gay-Lussac, to be a small Bar of iron, tapering, 
rom base to summit in form of a pyramid, and for a height 
30 feet, which is the mean length of stems placed on build- 
ings, the base should be about 24 iuches square. Iron bei 
liable to rust by action of air and, moisture, the point of the 
gtem would soon become blunt; and, therefore, to prevent 
it, a portion of the top, about 20 inches in length, should be 
a ‘conical stem of brass or copper, gilded at its extremity, or 
terminated by a small platina needle, two inches long. In- 
stead of the platina needle, one of standard silver may be 
substituted. The platina needle should be united by a silver 
solder to the copper stem ; and as it might separate, not- 
withstanding the solder, it should be further secured by a 
small collar of copper. e copper stem is united to the 
iron one means of a gudgeon, which screws into each : 
the gudgeon, being first united to the copper stem by two 
steady pins at rgb ianeles, is then to be screwed into the iron 
stem, and secured by a 
The conductorshould be 2 ? of an inch square, and, as already 
mentioned, should reach from the stem to the ground. it 
should be firmly united to the stem, by being jammed be- 
tween the two ears of a collar, by means of a bolt. The con- 
ductor should be supported parallel to the roof, about 6 
inches from it, by forked stanchions, and after turning over 
the cornice, without touching it, should be brought down the 
wall, to which it should be fastened by means of cramps. 
At the bottom of the wall, it should be bent at right angles, 
and carried in that direction 12 or 15 feet. 
Iron, in immediate contact with moist earth, soon becomes 
covered with rust, and in time is destroyed : to prevent this, 
the conductor should be placed .in a trough filled with char- 
coal, in the following manner. aving made a trench in the 
ground about two feet deep, a row of bricks is laid on the 
broad side, and covered by another row placed on the edge; 
