But ya can't get this riddle!?

[Josh W]

I was once so amazing that people would stop and stare for at me for hours. The first ones of me were very expensive and rare, but now I'm very commonplace. It's not clear if I was first seen in 1893 at the World Columbian Exposition in Chicago or in 1904 at the Louisiana Purchase Exposition in St. Louis. What am I and what element do I contain?

 

[Steffie-Elle]

TNT and Uranium

...or maybe Alexander Graham Bell's telephone(what element?...)

...or even Thomas Edison's CARBON COPY of Joseph Swan's light bulb

 

[Micery!!!!]

t.v???
u contain videos?