Checking my phone for the temperature, I see that its currently 91 degrees but it feels like 99. Got me wondering how thermometers work/how they came to be and how they calculate “what it feels like.”
In: Technology
Humans cool ourselves through evaporative cooling. We sweat, the sweat evaporates and takes substantial heat with it.
The ability for water to evaporate depends on the temperature, the relative humidity, and the air pressure. A “dry” 90 F means water evaporates quickly, while a wet 90 F means water does not evaporate well. The wet 90 F feels much hotter to humans.
The classic way to measure this phenomenon was with a thermometer with a wet cloth wrapped around it. This gives you the wet bulb temperature, which will be below the ambient air temperature.
Even in places that reach 110+ F, nowhere on earth ever reaches a wet bulb temperature above 100 F. In fact, sustained exposure to wet bulb temperatures in the 90 F range is highly fatal.
The most comfortable weather has a wet bulb temperature around 60 F or lower. The most miserable/hot places on earth tend to be in the mid 80 F range. 90+ is very rare. The heat index is the “feels like” temperature and is based on this concept.
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