The vibrations of solid bodies are accompanied by dissipation of energy attributable to their “ internal friction”; this loss of energy is additional to whatever external losses may occur. There are various ways of specifying the internal friction, and few of the published researches have adopted a common terminology. In this section the results have been reduced to show a dimensionless quantity, 1/Q, which may be called the “dissipation function” or the “internal friction.” The logarithmic decrement Δ of free vibrations is related to this function by Δ = π/Q. If dE is the loss of energy per cycle, and E the total energy, then 1/Q = dE/(2πE), Thus the internal friction is small when 1/Q is small.

Only in the last few years has the technique of measuring internal friction reached a point where the losses in single crystals can be studied [4, 16, 17]. The mechanism of internal dissipation of energy in single crystals probably involves plastic flow and strain hardening even for very small strains. The internal friction is sensitive to the condition of the surface and to annealing [16]. Unannealed single crystals may show losses approaching those of polycrystalline material. In the latter, internal friction arises from a number of distinct sources, including (1) losses within the individual crystals, (2) losses at the surfaces of the . . .