THE ELECTRIC ARC 



distinctly the boundary 

 between the carbon and 

 the luminous vapor. 

 An outline drawing as 

 given in Fig. 2 may be 

 helpful for this purpose. 

 The carbon with the 

 depression at the end 

 is the positive carbon, 

 or anode, as it is called, 

 while the pointed car- 

 bon is the negative end, 

 or cathode. The con- 

 cave part of the anode, 

 marked c, is intensely 

 luminous and is called 

 the crater. With this 

 form of arc by far the 

 greater part of the light comes from this crater. Since it is 

 usually desirable to have the light thrown on 

 the ground and not into the sky, the anode is 

 placed above and the cathode below. 



With homogeneous carbons this crater is 

 apt to form at one side, with the result that 

 much of the light is thrown to that side, while 

 the region on the other side is left in com- 

 parative darkness. It was found that this 

 could be largely remedied by making the 

 carbons hollow and filling the hollow space 

 with a softer quality of carbon. Such carbons 

 are called cored carbons and are commonly used for the 

 anode. Those which are not cored are called solid carbons. 



FIG. i. 



- C 



FIG. 2. 



