After several days of mild panic, the Dow Jones Industrial Average closed at 10172.60 Thursday, allowing Wall Street to breathe a sigh of relief. The index, which had languished below 10000 since last week, was buoyed by encouraging comments from the European Central Bank and promising economic data from the United States and China. And, with a late rally, its total gains for the day meant a 2.8 percent rise—the most progress in a single day since May 27. "The way the market moved late in the day is just icing on the cake," said one strategist. "We may be looking at the beginnings of a broader reversal here, but it will take a few more sessions like this to confirm that to the trading crowd."