FEBRUARY. W 



it is so in every case : the most minute crystal or point on 

 your sleeve is of faultless regularity and beauty. 



C. — How are the crystals on windows formed ? those 

 which are called frosted flowers^ and which are so often seen 

 in our bedrooms on cold mornings. 



F, — By the shooting out of radiating needles in the man- 

 ner I have described ; but why these crystals take the fan- 

 tastic forms of leaves and flowers, instead of regular angles, 

 I cannot explain. Perhaps^ if our instruments were of suffi- 

 cient power, we should find that the individual crystals do 

 shoot in the usual direction^, but are so minute that we lose 

 them in the whole. As an apparent circle may be foimed 

 of very short right lines. 



C. — When these leaf-like figures are large, they possess 

 considerable elegance. Why are they smaller in very cold 

 weather ? 



F. — Probably, because then the freezing or crystallization 

 begins at more points at once, each point being the centre 

 of its own radiation, and the needles meet each other at 

 shorter distances. But in milder weather, the surface not 

 being cooled so rapidly, the crystals have more time and 

 longer space to shoot in, and so make larger figures ; as there 

 are fewer centres of radiation. I have sometimes seen the 

 hoar frost stand up perpendicularly from the glass to the 

 height of half an inch, and nearly as thick as snow : but 

 this has been when the room has been much charged with 

 vapour, and the exterior air at a very low temperature. 



C — It is well we have gained the shelter of home : how 

 thickly and how fast the flakes of snow descend : they 

 coalesce, and are become quite large. 



F. — And how noiselessly they descend : it bids fair to be 

 a heavy fall : probably by the morning light a dense coat of 

 many inches will have covered the earth ; yet not the slightest 



