Electricity 



231 



FIG. 131. Feeling one live wire does not give her a shock, but what would 

 happen if she touched the gas pipe with her other hand? 



copper but of substances which do not conduct elec- 

 tricity nearly as well and which therefore have much 

 higher resistance. Carbon was once used, but now a 

 metal called tungsten is used for most incandescent 

 lamps. Both carbon and tungsten resist an electric 

 current so much that they are easily heated white hot 

 by it. On the other hand, they let so little current 

 through that what does pass flows through the larger 

 copper wires very easily and does not heat them notice- 

 ably. 



Experiment 70. Turn on the switch that lets the elec- 

 tricity flow through the long resistance wire that passes 

 around the porcelain posts. Watch the wire. 



The resistance wire you are using is an alloy, a mix- 

 ture of metals that will resist electricity much more 

 than ordinary metals will. This is the same kind of 



