Why does hay, if stacked when damp, take fire?

Because the moisture elevates the temperature sufficiently to produce
putrefaction, and the ensuing chemical action causes sufficient heat to
continue the process; the quantity of matter being also great, the heat
is proportional.

Why is the air warm in misty or rainy weather?

Because of the liberation of the latent heat from the precipitated
vapour.

Why is heated air thinner or lighter than cold air?

Because it is a property of heat to expand all bodies; or rather we
should say, that we call air hot or cold, according as it naturally is
more or less expanded.

Why is a tremulous motion observable over chimney-pots, and slated roofs
which have been heated by the sun?

Because the warm air rises, and its refracting power being less than
that of the colder air, the currents are rendered visible by the
distortion of objects viewed through them.

Within doors, a similar example occurs above the foot-lights of the
stage of a theatre; the flame of a candle, or the smoke of a lamp.

Why are the gas chandeliers in our theatres placed under a large funnel?