After nearly twenty years with the Gray Lady, columnist Bob Herbert will leave the New York Times to pursue book-writing and other longer-form opportunities. “The deadlines and demands were a useful discipline, but for some time now I have grown eager to move beyond the constriction of the column format, with its rigid 800-word limit, in favor of broader and more versatile efforts,” he said in a memo to staff today. “So I am leaving The New York Times and the rewards and rigors of daily journalism with the intent of writing more expansively and more aggressively about the injustices visited on working people, the poor and the many others in our society who find themselves on the wrong side of power.” His last column will appear this Saturday. “We will miss him and wish him the best,” said his soon-to-be former boss, opinion pages editor Andrew Rosenthal. “He was often called, ‘the conscience of the Times.’”