Hundreds of Americans headed to the National Mall in Washington, D.C. to mark a sweltering Fourth of July holiday.br br One of the nation's biggest fireworks parties went off without a hitch Wednesday (July 04) night, while many communities canceled annual displays due to dry conditions or a weak economy.br br Although the heat index again topped 100 F (37.8 C), the National Mall was crowded with holiday revelers.br br The fireworks launched over the Washington Monument as the National Symphony Orchestra simultaneously delivered a signature Independence Day rendition of Tchaikovsky's "1812 Overture.