JANUARY. 3 



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 



