At one time it was believed that heat was a liquid. Sure, that sounds kind of crazy, but if you think for a second, you might see why. Suppose you have an object that’s very hot — say a metal spoon that’s been sitting in hot coffee. Pick it up and you can feel the heat spreading to your hand. The longer you hold on, the more heat seems to enter your hand. Ouch! Well, maybe heat is an invisible liquid that pours from the spoon into your hand. After all, that theory fits all the evidence, doesn’t it? But there’s a problem. Another simple experiment you can do shows heat can’t be a liquid.

曾有一段时间，有人认为热量是液体。当然，这听起来有点疯狂，但如果你仔细想一想，您可能会明白其中的道理。假设你有一个很热的物体——放在热咖啡中的一个金属勺。拿起勺子，你能刚到热量蔓延到你的手，握的时间越长。传到你手上的热量越多。哎哟！好吧，也许热是一种无形的液体，它从勺子中倒入你的手中。毕竟，这理论符合所有的证据，不是吗？但是有一个问题。你可以做另外一个简单的实验，来证明热热量不是液体。