On the eve of the United States’ 250th birthday, in the nation’s capital, people were sweating through their shirts, and tourists were pressing electric fans directly to their foreheads. The record-breaking heat wave that roasted the Midwest earlier this week has turned Washington, D.C., into hell. Temperatures peaked at 102 degrees Fahrenheit, with a heat index of 117. The sky was cloudless, and the humidity was encouraging me to lie down and cry. It was difficult to believe that D.C. has been four degrees hotter than this twice before, in August 1918 and July 1930. Tomorrow may be even more surreal, with another day of oppressive heat and throngs of tourists in town to see what the president has billed as the biggest fireworks display in human history.On Tuesday, August 6, 1918, “so hot