Our understanding of the basic physics underlying the properties of ice has dramatically changed during the last half century. At the beginning of this period it was known that the water molecules in ice were arranged with tetrahedral hydrogen bonding, and it had just been established that the hydrogens were not crystallographically arranged on these bonds; however, the way in which water molecules could re-orient was unknown and the implications of this for the mechanical properties and hence for glacier flow were unexplored. The suggestion of electrical point defects in ice, the L and D defects of Bjerrum and the ionic defects, pointed the way to an understanding first of the dielectric relaxation and electrical conductivity of ice and then to a possible interaction between these electrical properties and the movement of dislocations, and hence the plastic deformation of ice.
Menwhile, much work was done to study the behaviour of ice under various physical conditions and to establish more rigorous laws for many physical properties of single crystals of ice and of various forms of polycrystalline ice, and much work was done to find the crystallographic structures of the various phases of ice including those already known to exist at high pressures. The intriguing appearance of a cubic form of ice at low temperatures was also investigated together with vitreous ice formed at even lower temperatures.
Many of these properties are of great interest to meteorologists trying to understand cloud physics and the physics of thunderstorm electricity as well as to astronomers thinking about ice in space, comets, the icy satellites of the planets, or even on the planets themselves.