Wall Street lower as nerves rise ahead of Yellen speech

While the Fed is widely expected to maintain rates at its September meeting, Yellen's language on Friday morning will be assessed to see whether she takes a more aggressive stance. Investors have been playing a waiting game all week, expecting Yellen to either endorse or dismiss the hawkish tone set by key policymakers, the latest from Kansas City Fed President and voting member, Esther George, on Thursday. "I do think it is time to move that rate," George told CNBC, arguing on the basis of prog