“It’s not the heat, it’s the humidity.” Anyone who has spent any time in the Midwest in the summer has heard that one. The truth is, it’s the heat AND the humidity. That’s what makes our hot weather special.

“It’s not the heat, it’s the humidity.”


Anyone who has spent any time in the Midwest in the summer has heard that one. The truth is, it’s the heat AND the humidity. That’s what makes our hot weather special.


And that’s the idea behind the “heat index,” which combines temperature and relative humidity to produce the “felt air temperature” — how hot it feels.


The heat index was adopted by the National Weather Service in 1979. It was based on work by Robert G. Steadman and developed and introduced in 1978 by early TV weather forecaster George Winterling. That’s right — the developer of the ultimate measure of summer was named “Winter-ling.”


The “relative humidity,” expressed as a percentage, is “the amount of moisture in the air as compared with the maximum amount that the air could contain at the same temperature.” In other words, how full of water is it?


When the relative humidity is high, the air has less room for our evaporating perspiration, which means we cool down slower — so we feel hotter longer.


And wouldn’t you just know it: The histories of the words “humidity” and “temperature” have something in common, and it has to do with our bodies.


In medieval physiology, the body was thought to contain four “cardinal humors”: blood, phlegm, choler and melancholy. An excess of any of these humors was believed to throw the body (and mind) out of balance, causing the respective conditions: sanguine, phlegmatic, choleric (or bilious) and melancholic “temperaments.”


“Humor” and “humidity” have in common the Latin verb “umere,” meaning “to be moist.”


According to “The Oxford Dictionary of Word Histories,” the notion of the bodily fluids led to “humor” meaning “state of mind, mood” and “whim, fancy” in the 16th century. So “to humor someone” became “to indulge a person’s whim.”


The association of “humor” with amusement didn’t come until the late 17th century.


“Temperature” and “temperament” come from the Latin verb “temperare,” meaning “to observe proper measure, mix, regulate, forbear.” This is a mixed-up word family.


“Temperance” is a temperament that focuses on self-restraint, particularly when it comes to alcoholic beverages. In such cases, it can refer to moderation or, in the extreme, abstinence.


And then there’s “temperate,” which appears to be the most even-tempered of the bunch. It also brings us back to the weather.


“Temperate,” when applied to weather conditions or climate, means “neither very hot nor very cold.”


When it gets temperate again outside, I expect to be in a better humor.


Contact Barry Wood at bwood@rrstar.com or read his blog at blogs.e-rockford.com/woodonwords/.