FEBRUARY. 
29 
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 formed 
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 
