We appreciate speed, as a tool of storytelling or just as a bright challenge to our senses. We admire speed, and always have, as raw virtuoso performance-Jascha Heifetz flashing through an encore piece, always teetering on the verge of breaking a string or flubbing a hemidemisemiquaver. True, allegros without adagios grow tiresome. Slow music can have its subtler kind of virtuosity, the weightlessness of a bicycle rider staying balanced while drifting to a halt. Gustav Mahler is supposed to have advised a young conductor: if you think you are boring your audience, slow down. If there is an ultimate limit to the pace of entertainment, we must now be approaching it, just as Olympic sprinters are approaching, asymptotically, the human limit for the hundred-yard dash. In some ways, we are past the limit. Any day now, lawyers will take note of the considerable quantities of television text-including copyright notices and advertising fine print-that flash by too fast for any human to read it.