Something is in short supply this television season. Lift an ear to the wind and hear the silence.
   You'll hear nary a peep of crowing from the broadcast networks over ratings since the attacks of six weeks ago.
   But while the silence can be refreshing, it means that some shows that are doing especially well, like CBS’s "Late Show" with David Letterman, are getting little notice.
   Ratings for Letterman’s show were up 33 percent among adults 18-49 four weeks after the terrorist attacks, compared to the four weeks before, putting it in a virtual tie with Jay Leno’s "Tonight Show."
   The Leno show also saw a spike but its ratings have since settled back to normal levels.
   Letterman's ratings may indeed level off as well, but they could just as well hold, or sink to a level well above where there were before.
   Letterman’s ratings spike is nothing short of historic, coming after years of heated rivalry in which Leno maintained a comfortable lead.
   The rivalry goes back to 1992 when Letterman was snubbed by NBC in favor of Leno for Johnny Carson’s vacated seat on the "Tonight Show."
   In the past, even the slightest uptick in Letterman's ratings was trumpeted by CBS's mighty PR engines as a come-from-behind victory. That makes the network's silence of recent weeks all the more amazing, if not downright confounding.
   Following his return to the air after the attacks, Letterman had ratings increases in just about every major demographic group.
   His show was up 33 percent among adults 18-34 for the week ending Oct. 12, for example, and 38 percent among adults 25-54.
    "People are going home, turning on the news and then after getting updates, they need to laugh or watch something familiar," says Stephen Calandra, senior partner and managing director of the consumer insights group at MindShare, explaining an overall increase in late night viewing.
    "People are tuning into the news and continuing to watch afterwards because who wants to go to bed depressed?"
    Why Letterman over Leno?
    Here's the speculation, and it is nothing more than that.
    Letterman is in New York, and since the attacks, America's eyes and hearts seem more directed toward the city generally, and with deeper appreciation, in some cases forgiving even the arrogance of its Yankees.
    It could be Letterman's easy access to Rudy Giuliani, the city's cantankerous mayor who has risen to the status of national darling for his performance in the aftermath of the Sept. 11 attacks.
    But just as likely, probably more so, when one thinks about it, is that not only did Letterman return to the air a night before Leno, but he opened his show with a monologue about the tragedy that was talked about for days afterwards for its seriousness and deep feeling.
    It may seem odd that, with all the chatter that spills out of television sets every day, one person's monologue could not only be remembered but could sustain a ratings increase, but it appears to be happening.
    "Letterman had the luck of getting great publicity," says Calandra. "He was very gracious in his opening remarks on that initial show."
    The percentage of adults 18-49 watching late-night TV on the Big Three networks, for example, was up about 11 percent for the four weeks following the terrorist attacks.
    ABC’s "Nightline" actually had the biggest increase. Its adult 18-49 rating was up 54 percent, to a 2.0, for the week ending Oct. 12.
    And Leno’s rating was up 5 percent, to a 2.1, and still ranked No. 1 by a thin margin. Letterman had a 2.0.
    Many TV shows, in fact, have had ratings increases in the days and weeks after major news stories.
    But seven weeks after the attacks, the increase in viewing is extending well beyond what media buyers typically expect.
     Back in 1991, late-night viewing went up for one week after the Gulf War. But that event was newsworthy for a relatively brief period.
    The ongoing war in Afghanistan and growing concerns about homeland security are unprecedented.
    "Today, it seems like every day there is an update and a new story unfolding," says Calandra. "That has kept people’s attention at high levels.
    "Ratings will eventually come down to more normal levels," he says.
    "But it’s a slightly changed world and people are realizing that they need to be more knowledgeable, and then there’s a residual effect in wanting to be entertained."