NO. 2 



HISTORY OF ELECTRIC LIGHT — SCHROEDER 



21 



down the tube so the two carbons normally were in contact. An 

 electro-magnet in series with the arc was so located that, when ener- 

 gized, it pulled up the iron tube. This magnet also held the brass 

 covered iron rod from pushing the upper carbon down the tube so that 

 the two carbons were pulled apart, striking the arc. When the arc 

 went out, the iron tube dropped back into its original position, the 

 brass covered iron rod was released, pushing the upper carbon down 

 the tube until the two carbons again touched. This closed the circuit 

 again, striking the arc as before. 



Roberts' Arc Lamp, 

 1852. 



The arc was controlled by an 

 electro-magnet which held an 

 iron tube to which the upper 

 carbon was fastened. 



Slater and Watson's Arc 

 Lamp, 1852. 



Clutches were used for the 

 first time in this arc lamp to 

 feed the carbons. 



In the same year (1852) Slater and Watson obtained an English 

 patent on an arc lamp in which the upper carbon was movable and 

 held in place by two clutches actuated by electro-magnets. The lower 

 carbon was fixed, and normally the two carbons touched each other. 

 When current was turned on, the electro-magnet lifted the clutches 

 which gripped the upper carbon, pulling it up and striking the arc. 

 This was the first time that a clutch was used to allow the carbon to 

 feed as it became consumed. 



Henry Chapman, in 1855. made an arc in which the upper carbon 

 was allowed to feed by gravity, but held in place by a chain wound 



