228 TKAXSACTIONS OF THK AMERICAN INSTITUTE. 



should never be insulated. It may be fastened to the building 

 with brackets of wood or staples. 



Points. — The attaching to the upper end of a lightning rod a 

 copper, silver, gold, or any kind of a point does not add to the 

 utility of the rod, but when attached always diminishes, more 

 or less, the conducting power of the rod by breaking up the 

 perfect continuity that a rod should possess, and interrupting its 

 polarity. 



Size. — An iron lightning rod should never have less than three 

 inches conducting surface, possessing solidity suiBcient to have 

 strength and durability. 



Construction. — A lightning rod should not ppssess in its con- 

 struction sharp edges — neither should it be in sections or pieces, 

 (the sections or pieces being hooked or screwed together) but it 

 should be all in one piece, possessing an equal, even, unbroken 

 surface in its whole length. 



Application. — In the application of the rod to the building the 

 conducting power of the building should be brought into the 

 general line of conduction ; that is, the rod should come in good 

 metallic contact with all the important metallic substances upon 

 the outside of the building, such as gutt-ers, spouts, &c. That 

 part of the rod that comes in contact with the earth, should be 

 increased in its surface and conducting power, so that there will 

 not be less conducting surface in contact with the earth than is 

 exposed to the building and atmosphere, and care should be 

 taken, that the earth around, and in contact with the rod is 

 always moist. 



Shade Trees. — Shade trees should not be relied upon as a pro- 

 tection from lightning, because their conducting power varies so 

 much, and very often, when in their best conducting condition, 

 they are damaged by the lightning passing over them. The con- 

 ducting power of shade trees then should be increased and made 

 permanent by the application of an iron or copper wire. 



Errors. — One of the errors committed in protecting from light- 

 ning is an improper estimate placed upon the conducting power 

 of the building, compared with the material used for protection. 

 When a lightning conductor terminates or ends in a substance of 

 imperfect or less conducting power, it is reduced to the conduct- 

 ing power of the body in which it ends. 



Dry earth is a non or imperfect conductor. Earth owes its 

 conducting power to water. According to Cavendish, the con- 



