ILLUMINATION AND PHOTOMETRY 



431 



connections. The watts per mean spherical candlepower run 

 alxmt 0.71. Comparing this figure with 0.43 watt per mean 

 spherical candlepower already given for the open flame arc, it will 

 be seen that long life is obtained at the expense of efficiency. 

 This type of lamp has one decided advantage over the magnetite 

 lamp in that it can be used with alternating current. 



Fio. 388. Mechanism and connections of Westinghouse loiiK-hurninK flame 

 arc, D. C. multiple type. 



196. The Metallic Electrode or Magnetite Lamp. The metal- 

 lic cirri r >de arc lamp or luminous arc or magnetite lamp, as it is 

 often called, differs from other arc lamps in that it employs metal- 

 lic electrodes and the light is derived from the arc itself. being 

 <lue to the luminescence of the vapor which comes from the 

 cathode or negative rlrrtrodr. The positive electrode is a large 

 cylinder of solid copper. The copper bring an excellent conduc- 

 tor of heat tends to keep moderately cool. The negative eler- 

 ifl made of an iron oxide containing titanium to give a white 

 light ( >ther Ingredients are added to give the electrode desirable 



burning eharaetrristics. 



A diagram of the lamp i< <lm\vn in I'ig. 389. The ft] 



-ts of negatively-charged lumin< - particle- \\hich 



originate at the negative electrode. The iron n\ides and the 



titanium of the negative elrrln.de give a wllite light. Heillg 



I. the g:i flie are >t rerun are rrprllrd 



