It allows you to define the concept of a thermometer. You have three objects, one of them could be a thermometer.

从热的物体流向冷的物体,由此我们可以定义温度，我们还可以用它来定义温度计：

麻省理工公开课 - 热力学与动力学课程节选

And Charles Darwin actually, who was an astute observer of human behavior, tells a nice story to illustrate this: how "a native touched with his finger some cold preserved meat and plainly showed disgust at its softness whilst I felt utter disgust at my food being touched by a naked savage though his hands did not appear dirty."

达尔文，对人类行为观察入微，他有一个故事很好地解释了反感：,“一个土著用手指碰冷腌肉,那种软软的质地让他感到很反感,而让我感无无比反感的是我的食物,被一个没穿衣取的土著碰了，虽然他的手不脏“

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