"Joe Egginton" wrote in message
...
Hello All,

As it's Christmas, I've had plenty of time on my hands! Here's a why
is it puzzle!

Why does water vapour condense at the bottom of a window pane first,
and then climb up the window.

Surely if the window is cold, then water vapour should condense on all
the window at the same time?

I would guess it's airflow down the cold pane as the air in contact with
the pane is cooled and sinks to be replaced by warmer air from the top
of the pane. The glass and air in contact are probably cooler at the
bottom of a pane hence more condensation, perhaps there is even some
evaporation at the top.

Tom