Sir,

I see that in Mr. M. M. Miller’s letter in the November 1952 issue of the Journal, page 150, the definition of firn suggested by the Committee on Snow Classification of the International Association of Scientific Hydrology is as follows:

If the words in brackets are to be considered part of the definition this will be a mistake. It may be true that in the Alps and most mountain regions firn is formed from snow in this way, but the greater part of the firn of the world, i.e. in the interior of polar ice caps, has never been subject to melting and freezing but is transformed “into a dense heavy material” by pressure and recrystallization only. It seems to me, therefore, that the suggested definition will lead to confusion, I would either omit the words in brackets altogether, or say “old snow which has outlasted one summer at least and is transformed into a dense material.” Polar, as indeed all, fun is characterized by the fact that (a) the particles are to some extent cemented together, but that (b) the air interstices still communicate with each other. (a) distinguishes it from snow, (b) from ice.