the columns in them would know how to resist the possible--but very
small--increase of temperature due to the excess of heat of one summer
above another. And since the eye is most struck by the appearance of the
stalagmites and ice-cascades, it may well be that the peasants have seen
these standing at the end of an unusually hot and dry summer, and have
thence concluded that hot summers are the best time for the formation of
ice. Of course, at the beginning of the winter after a hot summer, there
will be on these terms a larger nucleus of ice; and so it will become
true that the hotter the year, the more ice there will be, both during
the summer itself and after the following winter.

The further process of the formation of ice will be this:--the colds of
early winter will freeze all the water that may be in the glacières from
the summer's thaw, in such caves as do not possess a drainage, and then
the frost will have nothing to occupy itself upon but the ice already
formed, for no water can descend from the frost-bound surface of the
earth.[11] As soon as the snow begins to melt to so great a degree that
the fissures are opened up once more, the extremely cold water resulting
therefrom will descend through the limestone into a cave perfectly dry,
and filled with an atmosphere many degrees below the freezing point,
whose frost-power eagerly lays hold of every drop of water which does
not make its escape in time by the drainage of the cave. Thus the spring
months will be the great time of the formation of ice, and also of the
raising of the temperature from some degrees below freezing to the more
temperate register at which I have generally found it, viz., rather
above than below 32°. Professor Tyndall very properly likens the
external atmosphere to a ratchet-wheel, from its property of allowing
the passage of hot rays down to the surface of the earth, and resisting
their return: it may equally be so described on other grounds, inasmuch
as the cold and heavy atmosphere will sink in the winter into the pits