三伏天是一年中最難熬的日子，不僅是因?yàn)槿鞖鉁馗?，還因?yàn)槿鞚穸却蟆？諝庵械臐穸却鬄槭裁磿屛覀兏杏X更熱呢？

Humidity refers to the amount of water contained in the air. As the air’s temperature changes, so does the amount of water the air can hold.

濕度指的是空氣中所含的水分。隨著氣溫變化，空氣中的水分含量也會變化。

One of the ways your body cools itself is by sweating. The sweat then evaporates from your skin, and it carries heat away from the body as it leaves.

身體自我冷卻的方式之一就是出汗。汗水從你的皮膚表面蒸發(fā)時，會帶走身體的熱量。

However, humidity throws a wrench in that system of evaporative cooling. As relative humidity increases, the evaporation of sweat from your skin slows down. Instead, the sweat just drips, which leaves you with a damp T-shirt and none of the cooling effect. When the humidity spikes, we effectively lose a key tool that would normally cool us down.

然而，濕度卻會讓蒸發(fā)冷卻機(jī)制失靈。隨著空氣中的相對濕度增大，汗水從皮膚表面蒸發(fā)的速度則會減慢。停留在皮膚表面的汗水會把你的T恤浸濕，而且一點(diǎn)也不會讓你感到?jīng)隹?。?dāng)濕度很高時，我們實(shí)際上失去了一個自我降溫的法寶。

When we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

當(dāng)我們想到熱天里的風(fēng)，我們想到的是清涼宜人的微風(fēng)。正常情況下是如此的，但是當(dāng)天氣非常非常熱的時候（比如高于32攝氏度時），干燥的風(fēng)其實(shí)會讓我們更熱。在天氣很熱時，風(fēng)會在汗水尚未蒸發(fā)時就將其吹干，從而讓我們無法借助汗水蒸發(fā)來降溫。也正因如此，大熱天里的風(fēng)不僅不能帶來涼意，反而更像是烤箱的對流加熱。

However, being in the shade can make quite a big difference. Direct sunlight can add up to 15 degrees to the calculated heat index.

不過，在陰涼處則會有很大不同，因?yàn)殛柟庵鄙鋾屟谉嶂笖?shù)上升15度之多。

英文來源：Mental Floss

翻譯&編輯：丹妮