A small flask is filled with coloured water, and stopped with a cork.
Through the cork passes a glass tube water-tight, the liquid standing
at a certain height in the tube. The flask and its tube resemble the
bulb and stem of a thermometer. Applying the heat of a spirit-lamp,
the water rises in the tube, and finally trickles over the top.
Expansion by heat is thus illustrated.

Removing the lamp and piling a freezing mixture round the flask, the
liquid column falls, thus showing the contraction of the water by the
cold. But let the freezing mixture continue to act: the falling of the
column continues to a certain point; it then ceases. The top of the
column remains stationary for some seconds, and afterwards begins to
rise. The contraction has ceased, and _expansion by cold_ sets in. Let
the expansion continue till the liquid trickles a second time over the
top of the tube. The freezing mixture has here produced to all
appearance the same effect as the flame. In the case of water,
contraction by cold ceases, and expansion by cold sets in at the
definite temperature of 39° Fahr. Crystallization has virtually here
commenced, the molecules preparing themselves for the subsequent act
of solidification, which occurs at 32°, and in which the expansion
suddenly culminates. In virtue of this expansion, ice, as you know, is
lighter than water in the proportion of 8 to 9.[16]

A molecular problem of great interest is here involved, and I wish now
to place before you, for the satisfaction of your minds, a possible
solution of the problem:--

Consider, then, the ideal case of a number of magnets deprived of
weight, but retaining their polar forces. If we had a mobile liquid of