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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 76 



firmly screwed in the socket often caused the plaster base to pull apart, 

 SO the shape of the base was again changed early in 1 881, to the form 

 in use today. 



An improved method of connecting the ends of the filament to the 

 leading-in wires was adopted early in 1881. Formerly this was 

 accomplished by a delicate clamp having a bolt and nut. The improve- 

 ment consisted of copper plating the filament to the leading-in wire. 



In the early part of the year 1881 the lamps were made " eight to 



^b 



Original Screw Base 

 Lamp, 1880. 



This first screw base, con- 

 sisting of a screw shell and 

 ring for terminals with wood 

 for insulation, was a very 

 bulky affair. This lamp is in 

 the exhibit of Edison lamps in 

 the Smithsonian Institution. 



Improved Screw Base 

 Lamp, 1881. 



The terminals of this base 

 consisted of a cone shaped ring 

 and a screw shell. At first 

 wood was used for insulation, 

 later plaster of paris which 

 was also used to fasten the 

 base to the bulb. This lamp 

 is in the exhibit of Edison 

 lamps in the Smithsonian In- 

 stitution. 



the horsepower." Each lamp, therefore, consumed a little less than 

 100 watts, and was designed to give 16 candlepower in a horizontal 

 direction. The average candlepower (spherical) in all directions was 

 about 'jy per cent of this, hence as the modern term " lumen" is 12.57 

 spherical candlepower, these lamps had an initial efficiency of about 

 1.7 lumens per watt. The lamps blackened considerably during their 

 life so that just before they burned out their candlepower was less 

 than half that when new. Thus their mean efficiency throughout life 

 was about i.i 1-p-w (lumens per watt). These figures are interesting 



