I was working in a scrap yard in Southern England during summer vacation at an engineering university. I used to work repairing construction equipment.

One afternoon, I was taking apart a piling hammer that had some very large bolts holding it together. One of the nuts had corroded on to the bolt; to free it, I started heating the nut with an oxy-acetylene torch.

As I was doing this, one of the dimmest apprentices I have ever known came along. He asked me what I was doing. I patiently explained that if I heated the nut, it would grow larger and release its grip on the bolt so I could then remove it.

So things get larger when they get hot, do they? he asked.

Suddenly, an idea flashed into my mind (I know not from where.)

Yes, I said, thats why days are longer in summer and shorter in winter.

There was a long pause, then his face cleared.

You know, I always wondered about that, he said.