62 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



lighting service. This appHes also to all other countries in the world 

 except England where the bayonet form of base and socket is still 

 popular. 



THE EDISON " MUNICIPAL " STREET LIGHTING SYSTEM 



The arc lamp could not practically be made in a unit smaller than 

 the so-called "1200 candlepower " (6.6 ampere) or "half" size, 

 which really gave about 350 spherical candlepower. A demand there- 



l^msuN " MuNiLirAL " Svstem, 1885. 



High voltage direct current was generated, several circuits oper- 

 ating in multiple, three ampere lamps burning in series on each circuit. 

 Photograph courtesy of Association of Edison Illuminating Companies. 



fore arose for a small street lighting unit, and Edison designed his 

 " Municipal " street lighting system to fill this requirement. His 

 experience in the making of dynamos enabled him to make a direct 

 current bipolar constant potential machine that would deliver 1000 

 volts which later was increased to 1200 volts. They were first made 

 in two sizes having an output of 12 and 30 amperes respectively. 

 Incandescent lamps were made for 3 amperes in several sizes from 

 16 to 50 candlepower. These lamps were burned in series on the 

 1200-volt direct current system. Thus the 12-ampere machine had 

 a capacity for four series circuits, each taking 3 amperes, the series 



