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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



When the temperature of the platinum became too high, the rod in 

 expanding would short circuit the platinum. The platinum cooled 

 at once, the rod contracted opening the short circuit and allowing 

 current to flow through the burner again. His first incandescent lamp 

 patent covered this lamp. His next patent covered a similar lamp with 

 an improved thermostat consisting of an expanding diaphragm. Both 

 of these lamps were designed for use on series circuits. 



The only system of distributing electricity, known at that time, 



Edison's First Experimental Lamp, 1878. 



The burner was a coil of platinum wire which was protected from 

 operating at too high a temperature by a thermostat. 



was the series system. In this system current generated in the dynamo 

 armature flowed through the field coils, out to one lamp after another 

 over a wire, and then back to the dynamo. There were no means 

 by which one lamp could be turned on and ofif without doing the same 

 with all the others on the circuit. Edison realized that while this was 

 satisfactory for street lighting where arcs were generally used, it never 

 would be commercial for household lighting. He therefore decided 

 that a practical incandescent electric lighting system must be patterned 

 after gas lighting with which it would compete. He therefore made 



