264 THE POPULAR SCIENCE MONTHLY. 



try to pull it to pieces before your eyes. For this purpose I choose 

 ordinary ice, which is our commonest crystalline body. The agent to 

 be employed in taking down the molecules of the ice is a beam of heat. 

 Sent skillfully through the crystal, the beam selects certain points for 

 attack ; round about those points it works silently, taking down the 

 crystalline edifice, and reducing to the freedom of liquidity molecules 

 which had been previously locked in a firm, solid embrace. The lique- 

 fied spaces are rendered visible by strong illumination, and throwing 

 their magnified images on a screen. Starting from numerous points 

 in the ice we have expanding flowers, each with six petals, growing 

 larger and larger, and assuming, as they do so, beautifully crimped 

 borders ; showing, if I might use such tercns, the pains, and skill, and 

 exquisite sense of the beautiful, displayed by Nature in the formation 

 of a common block of ice. 



Here we have a process of demolition, which, however, clearly re- 

 veals the reverse process of erection. I wish, however, to show you 

 the molecules in the act of following their architectural instincts, and 

 building themselves together. You know how alum, and nitre, and 

 sugar crystals, are formed. The substance to be crystallized is dis- 

 solved in a liquid, and the liquid is permitted to evaporate. The solu- 

 tion soon becomes supersaturated, for none of the solid is carried away 

 by evaporation ; and then the molecules, no longer able to enjoy the 

 freedom of liquidity, close together and form crystals. My object now 

 is to make this process rapid enough to enable you to see it, and still 

 not too rapid to be followed by the eye. For this purpose a powerful 

 solar microscope and an intense source of light are needed. They are 

 both here. Pouring over a clean plate of glass a solution of sal-am- 

 monia, and placing the glass on its edge, the excess of the liquid flows 

 away, but a film clings to the glass. The beam employed to illuminate 

 this film hastens its evaporation, and brings it rapidly into a state of 

 supersaturation ; and now you see the orderly progress of the crystal- 

 lization over the entire screen. You may produce something similar 

 to this if you breathe upon the frost-ferns which overspread your win- 

 dow-panes in the winter, and permit the liquid to recrystallize. It 

 runs, as if alive, into the most beautiful forms. 



In this case the crystallizing force is hampered by the adhesion of 

 the liquid to the glass ; nevertheless, the play of power is strikingly 

 beautiful. In the next example our liquid will not be so much troubled 

 by its adhesion, for we shall liberate our atoms at a distance from the 

 surface of the glass. Sending an electric current through w r ater, we 

 decompose the liquid, and the bubbles of the constituent gases rise 

 before your eyes. Sending the same current through a solution of 

 acetate of lead, the lead is liberated, and its free atoms build them- 

 selves together to crystals of marvelous beauty. They grow before 

 you like sprouting ferns, exhibiting forms as wonderful as if they had 

 been produced by the play of vitality itself. I have seen these things 



