FAQs

Why does pressure fall off more slowly in warm air than cold air?

Richard C asks: From a previous question about the jet stream I have a problem understanding some key parts of the answer. Why does pressure fall off more slowly in warm air than cold air? And is the fact that this makes higher winds more westerly due to the exaggeration of the effect of the earth's rotation on pressure flow, in which case, can you explain this phenomenon?

The jet stream: chicken or egg?

Simeone Reginald asks: "When I look at forecast maps on westwind.ch that show the height of the 500mb layer and then look at the forecasts of the position of the jet stream, I notice that the jet stream almost always follows the dividing lines between the colder and warmer upper air masses. Does the position of the warm and cold upper air masses determine the route of the jet stream, or does the jet stream determine the position of the cold and warm upper air masses? Which is the chicken and which the egg?"

The winning question: How was the first thermometer calibrated?

The winning question (or, to be accurate, questions) in our Ask the Experts competition has been announced. Congratulations to Richard Ware for soundly testing their knowledge. Just to clarify, the image above is of Galileo, not Richard.

Question

a) How was the first thermometer calibrated?

b) What did Galileo use as a reference? Did he just get his pencil out and start marking the side of the thermometer ""10 ... 20 ... 30 ... 40"" etc?

c) Why did everyone (presumably) accept his findings as pukka? Did anyone query them?