| Show vy that hat is the best lightning rod A coln coin commission mission appointed by the french government to consider this subject concludes that square iron rods fifty nine hundredths of an inch square and several hundred feet in length are perfectly competent to convey lightning discharges of the usual nature to the ground and that copper conductors of the same section are still better than iron on account of the superior conducting power of copper A copper rod through which is discharged ob arged a large battery of leyden reyden jars which are ard charged to their utmost capacity can be held in 11 the hand while the discharge I 1 leaps aps to it and then passes through it to tile tilo ground the body in this case ia is a poor conductor compared with the rod and remains unaffected like the building which is thoroughly protected by a lightning rod having ing decided upon the size of our rod questions arise as to its tion to speak in general terms the better the tilo insulation the better the protection glass insulators of any ady form are buff bumm sufficient lelent even the wood of or the house itself is some times used but this insulation can not bo be depended depeu ded on the point most often overlooked is a proper conn connection action with the various bariou proper bell ropes and metallic pipes which run through P gh our buildings and with other metallic masses the light ning flash descending the lightning red often chooses to leap to some neighboring pipe or wire through intervening partitions of wood or stone before it seeks the ground supposing that our lightning conductor la Is of sufficient section and is connected with all outlying metallic masses of large extent how many projecting rods should we have and how high should they rise above the highest point in the building it is recommended by the french commission which we have already quoted and also by a commission appointed by the united states government to inquire in into to the protection of powder magazines magin that the height of the point of a lightning rod above the highest hl h point of a building to be protected io should be from nine and eight tenths feet to sixteen and four tenths according to circum stances and that it is almost always better to increase the number of the rods keeping within these limits and to join them all together by a common conductor than to increase the height of any ono one point paint 11 in reference to the best connection of rods with the ground the opinion is unanimous that the termination should be in moist ground or with wilh a system of water pipes it ia is ne necessary cesary to reach what is called the subterranean sheet of water that is the supplier of the various watercourses water courses wells and springs in short the toe vast vait area of good corl coil conducting ducting earth beneath sandy dy and rocky tracts which i are poor conductors atta atla atlantic antic affo anthly |
