A dense but fascinating examination of news journalism as an American institution. Mayer (Wall Street. Men and Money; Madison Avenue, USA; The Builders; The Lawyers; The Schools) here looks at news journalism, seeking not so much to editorialize upon it (though there is some of that) as to understand it, in all its sprawling complexity, as a profession. Taking specific news items that have dominated recent headlines--the Tylenol poisonings, the 1984 election, the explosion of the Challenger--he follows these events as stories in journalism, showing specifically how they broke and who broke them, picking them up from the points of view of different participants, and trying to assess the quality of their impact on American thinking. Interspersed with these narratives (the Tylenol section is the best) are gossipy historical pieces about the genesis of the different news media--particularly radio and TV--and how new technologies have changed the concept: of journalism in America. ""The social function of the news is to give the world coherence,"" Mayer writes. One of the questions he tries to answer--or at least raises, and allows us to answer--is the question of just how accurate or morally justifiable such ""coherence"" can ever be. This isn't easy to get through, and one suspects that those without a personal or professional interest in the subject may find it intimidating; but to those turned on by journalism's mystique, or who are concerned about the ethics of news-making in American life, it has much to say. A serious, often critical, ultimately sympathetic effort that goes a long way toward explaining an oft-maligned craft.