During a summer break from my studies at an engineering university, I worked in a scrap yard 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 onto the bolt, so I started heating the nut with an oxyacetylene torch. As I was doing this, one of the dimmest apprentices I have ever known came along and 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.