Stocks finished mixed Friday as volume declined for a second day in a row. The Nasdaq retreated 0.4%, partly because of Apple 's (AAPL) almost 3% decline. The NYSE composite and the S&P 500 added 0.4% and 0.3%, respectively. Volume fell across the board. Apple is acting as a drag on the Nasdaq, because of its 9.5% weighting in the index and the stock's 24% decline off its September high. The Nasdaq could become less captive to Apple's gyrations if