Five or six years ago, in the middle of an August heat wave, my wife finally prevailed on me to get an air conditioner. I like the heat, and for years I was able to get through New York summers without even the help of a fan.

But on this particular summer, the humidity was overwhelming. My resistance was overcome when, on a Saturday afternoon, we stepped outside into a city that looked like a set from some post-apocalypse movie. The air was filled with a fine, gritty, gray haze. The only people walking around were men with their shirts off, staggering about, waving their arms like survivors of some terrible catastrophe.

They were crazy, of course. Who else would stay outside on such an awful, muggy day? Summer brings the addled and the demented out into the streets of my Upper West Side neighborhood. I’m not talking about the homeless, who are always trying to survive out in the open, but that remarkable class of New Yorkers who seem completely out of their minds but are still somehow able to keep an apartment, even a job. They come out of an S.R.O. residence down on Broadway, or half-a-dozen other slightly dilapidated buildings in the area, and stand about the stoops and the street corners. Drunk or stoned, or just out of it; shouting or laughing hysterically at each other; more often brooding, looking haggard and dazed.

It’s the heat that brings them out, the tedium of staying cooped up in a close, stifling space. But it’s not just the poor or the already deranged who are driven mad by the weather. This is the silly season, when New Yorkers of all classes and incomes find their tempers flaring, their sanity loosening, and I’m not even talking about Park Avenue doctors blowing themselves up in their own townhouses. (That incident immediately set several people I know to speculating on how much more the cleared lot would be worth now that the house itself was gone — part of a more constant mania in this town.)

I suppose we should be glad that the city is now more staid and orderly than it’s ever been. Historically, summer is when things happen in New York. Tabloid murders and mob hits; blackouts and fires; strikes and riots; even, back in 1689, an attempted coup d’etat. Summer is when Beansy Rosenthal got it, drinking a horse’s neck down in Times Square; and Carmine Galante, dining al fresco at Joe and Mary’s, teeth clenched around his trademark cigar even in death. Summer is when Son of Sam and Crazy Joe Gallo both ran amok. It’s when the Stonewall rebellion took place, and the Dead Rabbit riot, and the draft riots, and the Orange riot, and the Harlem riots, and three separate Tompkins Square Park riots — and the police riot, when a pair of competing police departments brawled on the steps of City Hall. Summer is when the city is regularly stood on its head.

Small wonder that, back in the 19th century, the Board of Aldermen paid 50 cents for each head of an unmuzzled dog that anyone cared to turn in, fearful that any such strays could turn mad. It was said that the dogs developed an uncanny ability to disappear when the head choppers were about, but in any case one can’t help but wonder if the aldermen were wary of the wrong species. Who know what madness is simmering right now, within the walls of even our most stately domiciles?

A few days ago, I came across an anonymous letter left on a Riverside Park bench, calling the author’s fellow tenants to arms against a co-op or condo board. A page of pure vituperation excoriating the unfortunate board appeared under the sub-head: “So — now the revolt begins!”

Yes, indeed.