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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



piece of iron which could be drawn down into a coil of wire. The 

 weight of the lower electrode was overbalanced by a counterweight, 

 so that when no current was flowing the two carbons would touch. 

 When current was turned on, it flowed through the two carbons and 

 through the coil of wire (solenoid) which then became energized 

 and pulled the lower carbon down, thus striking the arc. Two of these 

 arc lamps were installed in Paris and caused considerable excitement. 

 After a few weeks of unreliable operation, it was found that the cost 

 of current from the batteries was much too great to continue their 



Archereau's Arc Lamp, i{ 



This simple arc was controlled by an electro-magnet, and two lamps 

 were installed for street lighting in Paris, current being obtained from 

 batteries. 



use commercially. The dynamo had not progressed far enough to 

 permit its use. 



joule's law 



Joule was an Englishman, and in 1842 began investigating the 

 relation between mechanical energy and heat. He first showed that, 

 by allowing a weight to drop from a considerable height and turn a 

 paddle wheel in water, the temperature of the water would increase 

 in relation to the work done in turning the wheel. It is now known 

 that 778 foot-pounds (i lb. falling 778 feet, 10 lbs. falling 77.8 feet 

 or 778 lbs. falling one foot, etc.) is the mechanical equivalent of 

 energy equal to raising one pound of water one degree Fahrenheit. 



