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 bo- 

 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 

 within 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- 



