From about 16 to 22 mins (use link below):
www.bbc.co.uk/iplayer/episode/b07l1zvw/forces-of-nature-with-brian-cox-3-the-moth-and-the-flame
Mike
www.bbc.co.uk/iplayer/episode/b07l1zvw/forces-of-nature-with-brian-cox-3-the-moth-and-the-flame
Mike