Abstract
The theories of the mean free path of electrons in various types of materials, under various conditions, are discussed. The conductivity, thermo-electric power, Hall coefficient, fractional change of conductivity in a magnetic field, and the Nernst, Ettinghausen and Righi-Leduc coefficients are all calculated upon the Lorentz-Sommerfeld theory for the various mean free path theories The variations are discussed with particular respect to the changes of the reduced chemical potential η*. The magnitude and sign of the coefficients are found to depend upon the mean free path theory assumed, that is, upon the type of material In particular it is shown that the Ettinghausen and Nernst coefficients should be negligible in the majority of semiconductors with ionic lattices. Some of the assumptions usually made in semiconductor theory are shown to lead to erroneous conclusions Experimental evidence is discussed and is found in general to support the theory given, both in impurity metals and semiconductors, except perhaps in the case of the thermo-electric power No experimental results in non-metals are known for the thermo- and galvano-magnetic effects apart from the Hall coefficient, and it appears likely that such measurements will produce interesting information
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