234 



Common Science 



FIG. 133. The pencil points are touched together and immediately drawn apart. 



the lead of the other pencil, and from that back through the 

 second wire to the other side of the knife switch and on 

 around the circuit, as shown in Figure 133. Keep the two 

 pencils apart and off the desk, while some one turns on the 

 snap switch and the " flush " switch that lets the electricity 

 through the resistance wire. Now bring the pencil points 

 together for an instant, immediately drawing them apart 

 about half an inch. You should get a brilliant white arc 

 light. 



Caution : Do not look at this brilliant arc for more than a 

 fraction of a second unless you look through a piece of smoked 

 or colored glass. 



Blow out the flame when the wood catches fire. After 

 you have done this two or three times, the inside of the wood 

 below the notches will be burned out so completely that you 

 can pull it off with your fingers, leaving the lead bare all the 

 way up to the wires. 



Let the class stand well back and watch the teacher do 

 the next part of the experiment. 



