I spent time in the Scottish hills last winter and on a couple of occasions I had cause to clean my glasses in a stream that originated from melting snow, effectively at 0 掳C. The water cooled the glass and its metal frame to such an extent that both lenses fell out. But how could this happen when, if I remember my A-level physics correctly, metal should contract more than optical glass because of a higher coefficient of expansion? Obviously this has never happened when I鈥檝e been walking around under normal conditions.
Andy Douse, Drumnadrochit, Invernesshire, UK