Oil Lightniug-Rods. o-io 



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 suflicient strength at 

 the base to resist the action of the wind, unless it were thick- 

 er at that end. An iron bar, about | of an inch, is sufficient 

 for the conductor of a lightning-rod. 



A hghtning-rod consists of two parts, the stem which pro- 

 jects above the roof into the air, and the conductor which 

 descends from the stem to the ground. The stem is pro- 

 posed by M. Gay-Lussac, to be a small bar of iron, tapering 

 from base to summit in form of a pyramid, and for a height 

 of 30 feet, which is the mean length of stems placed on build- 

 ings, the base should be about 2|^ inches square. Iron being 

 liable to rust by action of air and moisture, the point of the 

 stem 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. The copper stem is united to the 

 iron one by means of a gudgeon, which screws into each : 

 the gudgeon, being first united to the copper stem by two 

 steady pins at right angles, is then to be screwed into the iron 

 stem, and secured by a pin. 



The conductor should be f 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 G 

 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 lo feet. 



Iron, in immediate contact with moist earth, soon becomes 

 covered with rust, and in lime is destroyed : to prevent this, 

 the conductor should be placed in a trough filled with char- 

 coal, in the following manner. Having 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 : 



