Many years ago when people had no thermometers(温度计), they usually touched a thing to see how hot or cold it was. The following experiment shows how easy it was to make a mistake.
Take three glasses: the first with very hot water, the second one with very cold water, and the third one with water at room temperature. Then you put a finger of one hand in the hot water, and a finger of the other hand in the cold water. You hold your fingers in the two glasses for a minute. Then you use each finger, one after another, to see how hot or cold the water in the third glass is. You will find that the water is warm to the finger that was in the cold water before, but the finger which was in the hot water will feel cold in the same glass of water.
That is why you must always find the temperature in a scientific way. You must not try to tell the temperature as it seems to you.
You will often make a mistake if you take something that seems to you for a real fact. For example, when you are going to an amusement park by bus and you want to get there very quickly, it seems to you that your bus is going very slowly, slower than the other buses. But if it is Sunday and you have much free time, it seems to you all the buses and cars are going very fast.
