390 FRAGMENTS OF SCIENCE. 
pondering mind has forced upon it the question, How 
are they built up? We have obtained clear conceptions of 
polar force; and we infer from our broken magnet that 
polar force may be resident in the molecules or smallest 
particles of matter, and that by the play of this force 
structural arrangement is possible. What, in relation 
to our present question, is the natural action of a mind 
furnished with this knowledge? It is compelled to tran- 
scend experience, and endow the atoms and molecules of 
which crystals are built with definite poles whence issue 
attractions and repulsions. In virtue of these forces some 
poles are drawn together, while some retreat from each 
other; atom is added to atom, and molecule to molecule, 
not boisterously or fortuitously, but silently and symmet- 
rically, and in accordance with laws more rigid than those 
which guide a human builder when he places his materials 
together. Imagine the bricks and stones of this town of 
Dundee endowed with structural power. Imagine them 
attracting and repelling, and arranging themselves into 
streets and houses and Kinnaird Halls would not that be 
wonderful? Hardly less wonderful is the play of force 
by which the molecules of water build themselves into 
the sheets of ice which every winter roof your ponds and 
lakes. 
If I could show you the actual progress of this molecular 
architecture, its beauty would delight and astonish you. 
A reversal of the process of crystallization may be actually 
shown. The molecules of a piece of ice may be taken 
asunder before your eyes; and from the manner in which 
they separate you may to some extent infer the manner in 
which they go together. When a beam is sent from our 
electric lamp through a plate of glass, a portion of the 
beam is intercepted and the glass is warmed by the portion 
thus retained within it. When the beam is sent through a 
plate of ice, a portion of the beam is also absorbed ; but 
instead of warming the ice, the intercepted heat melts it 
internally. It is to the delicate, silent action of this beam 
Avithin the ice that I now wish to direct your attention. 
Upon the screen is thrown a magnified image of the slab of 
ice: the light of the beam passes freely through the ice 
without melting it, and enables us to form the image; but 
the heat is in great part intercepted, and that heat now 
applies itself to the work of internal liquefaction. Select- 
