The proposition that a glacier with a constant accumulation rate and no melting has a constant profile of density as a function of depth beneath the surface; by extension, and more loosely, the proposition that an unchanging density profile is sustained by the climatic mass balance. It follows from Sorge's law that a thickness change can be converted to an equivalent change of mass by multiplying by the density of glacier ice. This approach has been used in most mass-balancecalculations by geodetic methods. Sorge's law was originally introduced to describe densification of high polar snowpacks where melt is negligible. When Sorge's law is invoked in its looser sense, the constancy of the density profile is usually assumed rather than measured. The name, given by Bader (1954) in recognition of Ernst Sorge's observations in Greenland in 19301931, is pronounced as two syllables, the first stressed, with s as English z and with hard g.