70 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



Two sizes of lamps were made ; one for 6.6 amperes consuming 450 

 watts and having an efficiency of about 4^ lumens per watt, and the 

 other 7.5 amperes, 480 watts and 5 1-p-w (clear glassware). These 

 lamps soon superseded the direct current series arcs. They have now 

 been superseded by the more efficient magnetite arc and tungsten 

 filament incandescent lamps. 



SERIES INCANDESCENT LAMPS ON CONSTANT CURRENT TRANSFORMERS 



Series incandescent lamps were made for use on constant current 

 transformers superseding the " Alunicipal " and "Shunt Box" sys- 

 tems. The large Edison, now called the Mogul Screw base, was 

 adopted and the short circuiting film cut-out was removed from the 

 base and placed between prongs attached to the socket. 



Holder. Socket. Holder and socket. 



Series Incandescent Lamp Socket with Film Cutout, 1900. 



The " Large Edison," now called Mogul Screw, base was standardized 

 and the short circuiting device put on the socket terminals. 



The transformers made for the two sizes of arc lamps, produced 

 6.6 and 7.5 amperes and incandescent lamps, in various sizes from 

 16 to 50 cp, were made for these currents so that the incandescent 

 lamps could be operated on the same circuit with the arc lamps. The 

 carbon series incandescent lamp, however, was more efficient if made 

 for lower currents, so 3^-, 4- and 5|-ampere constant current trans- 

 formers were made for incandescent lamps designed for these am- 

 peres. Later, however, with the advent of the tungsten filament, the 

 6.6-ampere series tungsten lamp was made the standard, as it was 

 slightly more efficient than the lower current lamps, and was made 

 in sizes from 32 to 400 cp. When the more efficient gas-filled 

 tungsten lamps were developed, the sizes were further increased ; 

 the standard 6.6-ampere lamps now made are from 60 to 2500 cp. 



