176 ihe foems or water in 



§ 61. TAe 2>Zi^ Veins of Glaciers. 



445. We now approach the end, one important 

 question only remaining to be discussed. Hitherto we 

 have kept it back, for a wide acquaintance with the 

 glaciers was necessary to its solution. We had also 

 to make ourselves familiar by actual experiment with 

 the power of ice, softened by thaw, to yield to pressure, 

 and to liquefy under such pressure. 



446. Snow is white. But if you examine its in- 

 dividual particles you would call them transparent, not 

 white. The whiteness arises from the mixture of the 

 ice particles with small spaces of air. In the case of 

 all transparent bodies whiteness results from such a 

 mixture. The clearest glass or crystal when crushed 

 becomes a white powder. The foam of champagne is 

 white through the intimate admixture of a transparent 

 liquid with transparent carbonic acid gas. The whitest 

 paper, moreover, is composed of fibres which are in- 

 dividually transparent. 



447. It is not, however, the air or the gas, but the 

 optical severance of the particles, giving rise to a mul- 

 titude of reflexions of the white solar light nt their 

 surfaces, that produces the whiteness. 



448. The whiteness of the surface of a clean glacier 

 (112), and of the icebergs of the Margelin See (357), 

 has been already referred to a similar cause. The 

 surface is broken into innumerable fissures by the solar 



