328 



ELEMENTS OF ELECTRICAL ENGINEERING. 



a column of intensely heated vapor which conducts the electric 

 current across from one carbon rod to the other. 



An interior view of a typical direct-current enclosed-arc lamp 

 is shown in Fig. 180, and the same lamp is shown in Fig. 181 

 with its casing and outer globe complete. This lamp is designed 

 to operate across constant-voltage mains, it has a resistance coil 

 connected in series with the arc, and the arc is enclosed in a 



Fig. 180. 



Fig. 181. 



nearly air-tight bulb of thin opal glass into the ends of which the 

 carbon rods project. 



The mechanism of this lamp is operated by a plunger-type 

 electromagnet with its winding in series with the arc. The 

 plunger of this electromagnet actuates a lever to which is fixed a 

 clutch that grips the upper carbon. When the lamp switch is 

 open the clutch lies against a trigger which releases the carbon 

 and allows it to fall and make contact with the lower carbon. 



