194 HIDDEN BEAUTIES OF NATURE 



opaque to our vision. This arises, it is thought, from 

 the fact that each crystal contains air. This causes 

 the light to be internally reflected. A similar effect 

 is noticed by every one examining pond water under 

 the microscope. A bubble of air is present, and 

 with the exception of a tiny point of white in 

 its centre, the whole bubble appears to be black, the 

 light being internally reflected except at the central 

 point, through which the rays pass in a vertical 

 direction to the eye. Bulk for bulk ice contains less 

 air than snow, and is therefore much more trans- 

 parent. The crystals of snow are, however, so 

 wonderfully arranged that they all unite in reflecting 

 to the eye from their own surfaces the greatest 

 possible amount of light, thus producing the sensation 

 of whiteness. 



Dr. Scoresby sketched out ninety-six different 

 forms of snow-crystals during one of his voyages in 

 the Arctic regions. The presence of animal or 

 vegetable organisms occasionally adds colour to the 

 snow, so that at times in northern climates it appears 

 of a red or orange colour. 



Snow-water is said to contain a greater percentage 

 of oxygen than either rain or river water. 



This may be proved by analysis ; but if three bars 

 of iron of uniform quality be exposed to the action 

 of river-water, rain, and snow, respectively, that under 

 the influence of snow will be found to have oxidised 

 more than the others. Its rust will be more ap- 

 parent. 



