A man was working in a scrap yard during summer vacation at an engineering university.

One afternoon, he 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, he started heating the nut with an oxy-acetylene torch.

As he was doing this, one of the dimmest apprentices, Banta, came along. He asked him what he was doing.

He patiently explained that if he heated the nut, it would grow larger and release its grip on the bolt so he could then remove it.

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

Suddenly, an idea flashed into his mind, "Yes," he said, "that's 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.