JANUARY. 
S 
C, — What loud noise is that in the forest ? It sounds 
like the report of a large gun. I heard it too, while you 
were speaking. 
F, — It was the expansion of a tree. Old trees, when cut 
down^ are often found to have the heart-wood so separated 
from the sap-wood, as to fall apart when a log is split 
through the centre ; and we find that the crevice or interme- 
diate space has been occupied by a film of ice. This explains 
those loud reports which we heard just now, and which so 
often occur in the forest in frosty weather. Some water has 
lodged in the tree — perhaps in some maggot's or wood- 
pecker's hole, — which, freezing, rends the wood by its irresist- 
ible force of expansion ; into the rent so formed, the water 
percolates as soon as a thaw comes, and freezing again, ex- 
tends the crevice downwards, each rent attended with these 
sudden and startling sounds. Sometimes we may observe a 
long crack in the trunk of a tree, extending through the sap- 
wood and bark; and often an old bough is found to be nearly 
torn from the trunk ; both of which, I suppose, are caused 
by the same occurrence, the freezing of water. 
C. — How dazzling the snow is in the sunshine ! Why 
is it opaque and white, instead of being transparent and co- 
lourless as ice ? Is there any difference in the formation of 
the two ? 
F, — I believe not. The reason of the opacity and white- 
ness of snow is, that it is composed of very minute films of 
ice, which in falling rest in every possible angle, and reflect 
the light in every possible direction : if you take a single 
crystal of snow, you will see that it is perfectly transparent ; 
and if all the particles rested on each other in the same plane, 
the whole mass would be transparent as a similar mass of 
B 2 
