CLOUDS AND RIVEKS, ICE AND GLACTBRS. 35 



§ 11. Architecture of Lake Ice. 



96. Wo liave thus made ourselves acquainted with 

 the beautiful snow-flowers self-constructed by the 

 molecules of water in calm cold air. Do the mole- 

 cules show this architectural power when ordinary 

 water is frozen ? What, for example, is the structure 

 of the ice over which we skate in winter ? Quite as 

 wonderful as the flowers of the snow. The observation 

 is rare, if not new, but I have seen in water slowly 

 freezing six-rayed ice-stars formed, and floating free 

 on the surface. A six-rayed star, moreover, is typical 

 of the construction of all our lake ice. It is built up 

 of such forms wonderfully interlaced. 



97. Take a slab of lake ice and place it in the path 

 cr a concentrated sunbeam. Watch the track of the 

 beam through the ice. Part of the beam is stopped, 

 part of it goes through ; the former produces interna] 

 liquefaction, the latter has no effect whatever upon the 

 ice. But the liquefaction is not uniformly diffused. 

 From separate spots of the ice little shining points are 

 seen to sparkle forth. Every one of those points is sur- 

 rounded by a beautiful liquid flower with six petals. 



98. Ice and water are so optically alike that unless 

 the light fall properly upon these flowers you cannot 

 see them. But what is the central spot ? A vacuum. 

 Ice swims on water because, bulk for bulk, it is lio-ht^r 



