When I was at school it was still the day of coal fires in open grates. We had a teacher called Mr Chester-Master, who one day held forth in disbelief of the 'old wives' tale' that the sun shining on to a coal fire would make it go out.
That same year I read about Le Chatelier's Principle in a texbook on physical chemistry. This says, in effect,
A system in equilibrium which experiences an external influence will alter in such a way as to resist change.
This makes it obvious that a fire burning in a settled way (making it a system in equilibrium), if subjected to the sun's heat, will begin to die down. It is not just the brightness of the sun making the glow of the fire less prominent.
Unfortunately, it was not feasible for me to approach the teacher on this matter.
Last updated: 04 January 2005