74 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



coil of the auto transformer is connected through an induction coil 

 to the other end of the tube. By this means the alternating current 

 impulses are sent through the tube in one direction, one half cycle 

 from one of the pairs of terminals of the tube, the other half cycle 

 from the other terminal. Thus pulsating direct current, kept constant 

 by the induction coil, flows through the tube, the pulsations over- 

 lapping each other by the magnetic action of the choke coils. This 

 alternating current lamp is started by the high voltage discharge 

 method. It has a 50-inch length of tube, consuming about 400 watts 



fro/js/brmer 



Pesistonce 



/^Je/vury 



Storti/ip iK^ncf 



Diagram of Cooper-Hewitt Lamp for Use on Alternating Current. 



The mercury arc is inherently for use on direct current, but 

 by means of reactance coils, it can be operated on alternating 

 current. 



on 1 10 volts. Its efficiency is a little less than that of the direct current 

 lamp. 



THE LUMINOUS OR MAGNETITE ARC LAMP 



About 1901 Dr. Charles P. Steinmetz, Schenectady, N. Y., studied 

 the effect of metallic salts in the arc flame. Dr. Willis R. Whitney, 

 also of Schenectady, and director of the research laboratory of the 

 organization of which Dr. Steinmetz is the consulting engineer, fol- 

 lowed with some further work along this line. The results of this 

 work were incorporated in a commercial lamp called the magnetite arc 

 lamp, through the efforts of C. A. B. Halvorson, Jr., at Lynn, Mass. 

 The negative electrode consists of a pulverized mixture of magnetite 



