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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



an iron wire mounted in a bulb filled with hydrogen gas and was called 

 a " ballast." Iron has the property of increasing in resistance with 

 increase in current flowing through it, this increase being very marked 

 between certain temperatures at which the ballast was operated. The 

 lamp was put on the American market in 1900 for use on 220-volt 

 alternating current circuits. The glower consumed 0.4 ampere. 

 One, two, three, four and six glower lamps were made, consuming 

 88, 196, 274, 392 and 528 watts respectively. As most of the light 

 is thrown downward, their light output was generally given in mean 

 lower hemispherical candlepower. The multiple glower lamps were 





Diagram of Nernst Lamp. 



more efficient than the single glower, owing to the heat radiated from 

 one glower to another. Their efficiencies, depending on the size, were 

 from about 3^ to 5 lumens per watt, and their average candlepower 

 throughout life was about 80 per cent of initial. The lamp disap- 

 peared from the market about 191 2. 



THE COOPER-HEWITT LAMP 



In i860 Way discovered that if an electric circuit was opened 

 between mercury contacts a brilliant greenish colored arc was pro- 

 duced. Mercury was an expensive metal and as the carbon arc seemed 

 to give the most desirable results, nothing further was done for many 

 years until Dr. Peter Cooper Hewitt, an American, began experiment- 



