Conductivity and Cost 



329 



The conductor, or so-called "rod," first de- 

 mands attention. All metals conduct electricity 

 to some extent, but certain ones are very much 

 better than others. For example, lead, plati- 

 num, brass, and iron are poor conductors, which 



^N.^'"^ 



Fig. 134. Proper adjustment of lightning rods on a barn. 



is equivalent to saying that they heat up readily 

 on the passage of an electric current. On the 

 other hand, silver, copper, and aluminum are 

 good conductors. In. making a lightning rod, 

 the best all-round conductor should be used, 

 when cost and conductivity are the basis for the 

 selection. As an example, take the metals iron, 

 copper, and aluminum for comparison. Iron is 

 cheapest in price per pound, but its electrical 

 conductivity is small, while copper, though more 



