A. Because water does not cool down at sun-set, so fast as the land does; and, therefore, the air in contact with it is warmer.
Q. Why does not water cool down so fast as land?
A. 1st—Because the surface of water is perpetually changing, and as fast as one surface is made cold, another is presented: and
2ndly—The moment water is made cold it sinks, and warmer portions of water rise to occupy its place: therefore, before the surface of water is cooled, the whole volume must be made cold; which is not the case with land.
Q. What is the cause of a “pea-soup” london fog?
A. These fogs (which occur generally in the winter time) are occasioned thus:—Some current of air (being suddenly cooled) descends into the warm streets, preventing the rise of the smoke, and forcing it back in a mass towards the earth.
Q. Why are there not always fogs every night?
A. Because the air will always hold in solution a certain quantity of vapour, (which varies according to its temperature): and when the air is not saturated with vapour, it may be condensed without parting with it.
Q. Why are there ever fogs at night?