We were taught at school that hot air rises. So why does it get cooler as you go up a mountain?

The atmosphere is not warmed directly by the Sun, but by its radiation reflected off the Earth that is from below. So the higher you go from the Earth’s surface the colder it gets. Parcels of hot air do rise through the atmosphere, causing fluffy clouds, but sometimes much larger masses of warm air are forced up, as in a depression, or are displaced upwards by cold air sinking on a winter night. Then the atmosphere does get warmer as you go up, a condition known as temperature inversion.

Carole Chapman, Colchester

You have to distinguish heat from temperature. Temperature measures the degree of excitation (movement) of the molecules which compose an amount of matter.

Heat, however, is the measure of the amount of “hotness” in a substance, which depends on the temperature but also the amount of the matter.

The degree of warmth or cold you perceive is therefore a combination of the temperature of the surrounding air, but also its density — the amount there is of it. You feel cooler on top of a mountain because although the temperature may still be high, the air is thinner, so there is less matter, and therefore less heat.

Back in the 1960s it was almost a standard GCE O-level question to ask: “Why can you not make a good cup of tea on top of the Stelvio Pass? \”.

The answer was that in the thin atmosphere at that height, water would boil at a lower temperature than at sea level because there was less air, therefore less pressure on the water, and therefore the molecules of the water were already more fluid and would turn into steam quicker — at a lower temperature. Water at 85C instead of the 100C at sea level would not brew the tea nearly as well. QED.

Edwin H. Cox, London SE4

Why is the waiting room at a radio or television studio usually referred to as the green room?

This would appear to be a transference of usage from theatrical tradition. The green room is a designated area or room backstage in a theatre where performers enjoy moments of rest or refreshment between appearances on stage; the same term can be used for the hospitality room in a television studio.

The etymology is doubtful, and largely anecdotal. The OED suggests that the rest area was “probably . . . originally painted green”. There are fanciful theories too involving the early form of theatre lighting with its green hue — the limelight. The explanation given to me three decades ago (when I was with D’Oyly Carte) was that touring players would traditionally perform on the village green, setting up a simple platform for the stage. Actors would either be “treading the boards”, that is, be on stage — or be relaxing off stage, on the green.

Paul Seeley, Heaton, Bradford

The origin of “the green room” as a waiting area goes back far farther than radio and television. In medieval times strolling players would perform on village greens and prepare in rooms in nearby homes or inns, where a “green room” was provided. Even as late as the mid-20th century, actor “laddies” would sometimes refer to the stage as “the green”.

Eden Phillips, London E5

Why do some MPs turn and face the Chair on leaving the chamber and others don’t?

Peter Hughes, Burnham Bucks.

Much faith is now placed on carbon dating. On what is this based and how do scientists know that the age of the item is correct?

Peter A. Rushforth, West Yorkshire