MATTER AND FOKCE. 65 



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 lake?. 



If I could show you the actual progress of this mole- 

 cular architecture, its beauty would delight and astonish 

 you. A reversal of the process of crystallisation 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. Selecting certain 

 points for attack, round about those points the beam 

 works silently, undoing the crystalline architecture, 

 and reducing to the freedom of liquidity molecules 

 which had been previously locked in a solid embrace. 

 The liquefied spaces are rendered visible by strong il- 

 lumination. Observe those six-petaled flowers breaking 

 out over the white surface, and expanding in size as 

 the action of the beam continues. These flowers are 

 liquefied ice. Under the action of the heat the 



