178 Introduction to the Study of Science 



working plants, textile, glass, paper, and clothing manufactories, 

 in newspaper and printing establishments, in power houses, and 

 in photographic studios. 



The mercury vapor lamp. The Cooper-Hewitt mercury 

 vapor lamp (Fig. 53) comprises a clear glass tube that may be 

 twenty to fifty inches long, a reflector-holder, and an auxiliary. 

 The reflector-holder supports the glass tube and is connected 

 with the auxiliary. The reflector is usually polished white 

 porcelain and flat for general light distribution or curved for 



Connecting Wres 



Positive 

 E/ectrode 



, Negative 

 E/ectrode 



FIG. 53. A Cooper-Hewitt Mercury Vapor Lamp. 



concentrated light. The auxiliary contains the mechanism 

 for starting the lamp and regulates the supply of electric current. 

 One end of the tube is oval and contains a small amount of 

 metallic mercury. Both ends contain electrodes. The end 

 containing the mercury is called the negative electrode, which 

 means the way by which the electric current leaves the tube. The 

 other end is the positive electrode or the way by which the current 

 enters the tube. In each end of the tube are sealed platinum, 

 wires which serve as terminal connections. The air" is ex- 

 hausted from the tube before it is sealed. 



Quality of mercury vapor light. The quality of the mercury 

 vapor light is peculiar as may be observed in its effect upon 

 certain colors. Blue and green are made more intense; the 



