What does "in the heat of the night" mean?

In Dutch, you have 'in de HOLST' of the night, meaning the time between about 1.30 and 3.30. Might there be some etymological connection between this 'holst' and 'heat', possibly via descendants of Dutch immigrants into the USA?

The phrase "the heat of the night" appears at least as early as in Hermann Hagedorn, "A Boys' Life of Roosevelt," in Boys' Life (November 18, 1918), in a scene set in Kenya:

At last the stars began to pale; to the heat of the night succeeded the more merciless heat of the day. Higher and higher rose the sun. The sweat streamed down our faces, and the bodies of the black men glistened like oiled iron.

One of the characteristics of the U.S. South—at least at lower elevations during the summer—is that the air rarely feels cool even at night. I grew up in southern Texas (average daily high temperatures in August, 92°F to 94°F; average daily low temperatures, 74°F to 76°F) and never realized how unusual this phenomenon was until I moved to Washington, D.C., in August of one year, and noticed that the air felt slightly cool in the middle of the night—although people there were complaining about how hot it was. To me, "in the heat of the night" memorializes the distinctive strangeness (from a Northerner's perspective) of nights that never really cease to be warm.

The plot of the 1967 movie In the Heat of the Night, which seems to have been responsible for popularizing the expression, involves a collaboration between a black homicide detective from Philadelphia and the white police chief of Sparta, Mississippi, to solve a murder case in Sparta—and I had always imagined that the title referred to the Philadelphia detective's experience of the weather. Sparta is located in the Deep South about an equidistant from Memphis, Tennessee (to the northwest), and Jackson, Mississippi (to the southwest).

As it turns out, however, the nights, aren't much hotter on average in Sparta than they are in Philadelphia—at least not during August. Average daily temperature highs and lows in Sparta during the first half of August are 92°F and 70°F and during the second half are 91°F and 69°F; in Philadelphia, the average daily temperatures historically range from a high of 86°F and low of 70°F on August 1 to a high of 81°F and a low of 66°F on August 31.

Even so, for many people accustomed to cooler, drier climates, temperatures that stubbornly and consistently remain in the middle 70s for much of the night, with high humidity, are a remarkably unpleasant thing and fully justify the expression "in the heat of the night."

I understand that in the sixties, a heater was slang for a gun, and heat was Ghetto slang for police. Thus one might translate the title as The Black Policeman (since the night is black), and since it is about Virgil Tibbs, a black detective. The movie, and the tv series, are both based in the fictional town of Sparta Mississippi, a former confederate state, perhaps to give the movie/series an edge, whereas the novel Sparta is in N. Carolina not a former confederate state. The title may therefore indicate the heat of passionate anger and racial hatred, as well as have a sexual overtone... the story begins on a hot steamy night where air-conditioning is not working, and a nude girl (Too hot to dress?) parades deliberately in front of an open window. Heat, generally, does seem to be a leitmotif here and there.

The situation does not seem to have changed sadly in the South. In the TV series Virgil comments to a black friend "Things never change, they are just dressed up differently". In the episode Time for a Stranger (not written by the original author!) a teenage character comments to the Sheriff "serious enough to bring in the heat"... meaning the police ; the tv series was written and filmed in the nineties but evidently the phrase was still used. As for The Bottoms, where the poor black folk live, apparently this is a real place in Central Ohio, but does not have there quite the pejorative connotation as in the TV series.

It is a great title to think about its meaning, and a great question....

later comment One of the great,enriching things about good literature is working out, like a detective, some of the meanings an author might have or have had in mind, if any... it is purely speculative of course unless the author , alive or dead, can give some hints or positive answers... but I do not believe there is any such thing as over thinking. but rather literary analysis and not always taking everything simply at face value, otherwise one loses a great deal. Obviously any twit knows heat means hot , sweaty and possibly uncomfortable, but perhaps it means more than just the obvious here