On cold mornings I notice that train windows mist up on the inside. Once the outside temperature reaches about 6 or 7 掳C the windows normally clear. If it is raining, however, the windows mist up at these temperatures or even higher. Why does rain on the outside of the train, even at higher temperatures, cause the inside of the windows to mist up?
Klaus Forroby, North Harrow, Middlesex, UK