434 • M. Gay-Lussac on [Dec. 



T)' E', which is represented on a larger scale at fig. 13. The 

 trough is constructed in the following manner: — 



Having made a trench in the soil about two feet deep, a row 

 of bricks is laid on their broad faces, and on them others on 

 edge; a stratum of baker's ashes (braise de boulanger) is then 

 strewed over the bottom bricks, about two inches thick, on 

 which the conductor is laid, and the trough then filled up with 

 more ashes, and closed by a row of bricks laid along the top. 

 Tiles, stone or wood, will serve for making the trough, as well 

 •as bricks. Iron thus buried in charcoal will undergo no change 

 in the course of 30 years. But charcoal not merely prevents the 

 iron from rusting, for being a very good conductor of electricity, 

 after having been heated to redness (and that is the reason why 

 we recommend the use of baker's ashes), it facilitates the pas- 

 sage of the lightning into the ground. 



After leaving the trough, the conductor passes through the 

 side of the well, and descends into the water to the depth of at 

 least two feet below the lowest water line. The extremity of the 

 conductor usually terminates in two or three branches, to give a 

 readier passage to the lightning into the water. If the well be 

 situated in the interior of the building, the wall of the latter 

 must be pierced below the surface of the ground, and the con- 

 ductor passed through it into the well. 



If there be no well at hand, a hole must be made in the 

 ground with a six inch auger to the depth of 10 or 15 feet, and 

 the conductor passed to the bottom of it, placing it carefully in 

 the centre of the hole, which is then to be filled up with baker's 

 ashes rammed down as hard as possible all round the conductor. 

 But if expense be no object, it is better to sink a much wider 

 hole, E' F', at least 16 feet deep (unless water be met with at a 

 less depth), and make the extremity of the conductor terminate 

 in several branches, which must be surrounded by charcoal as 

 before, if not immersed in water, and the conductor itself be 

 similarly surrounded by it, by means of a wooden case filled 

 with the ashes. 



In a dry soil, or on a rock, the trench to receive the conductor 

 should be at least twice as long as that for. a common soil, and 

 even longer, if thereby it be possible to reach moist ground. 

 Should the situation not admit of the trench being much 

 increased in length, others, in a transverse direction, must 

 be made as seen at A, figs. 17 and 18, in which small bars of 

 iron surrounded by ashes are placed, and connected with the 

 conductor. In all cases the extremity of the conductor should 

 .terminate in several branches, and pass into a wide hole well 

 .filled with the ashes or charcoal that has been ignited. 



In general the trench should be made in the dampest, and 

 consequently lowest spot near the building, and the water- 



