Here's The Joke

I was working in a scrap yard during summer vacation at 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. "Yes," I 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.