191 Apart from numerous difficulties arising from the high pressure technique as such, there is a natural limitation to the possibility of applying a hydrostatic pressure, since liquids under pressure will solidify above a certain pressure limit. 8 2 Up to pressures of 3 X 10 kg.jm. at room temperature, a liquid like isopentane can be used. For higher pressures helium gas may be used, perhaps to about 9 2 10 kg.jm. , but BRIDGMAN already encountered enormous leakage difficulties 7 when using this gas at 7.10 kg.jm.2 at 90° K. A solution has been found by applying mechanical pressure for the range 8 9 2 between 3 X 10 and 10 kg.jm. , by using silver chloride as transmittant. In this case, however, one has to apply unknown corrections for shearing stress and deformation of the sample, a problem which BRIDGMAN solved experimentally by a determination of the resistivity in the pressure region between 2 and 8 2 5 X 10 kg.jm. , by the hydrostatic and by the mechanical pressure method as well, and applying the correction factor thus determined to the results obtained at higher pressures. Though this method seems to be right in good approximation, the data for the highest pressures are to be considered as less accurate.

Inhalt
The electronic structure of solids.- I. The periodic potential problem: General properties.- II. The periodic potential problem: Methods and results.- III. The self-consistent field.- IV. One-electron theory of properties of solids.- V. Impurity atoms and alloys.- VI. Crystalline binding energy, correlation and elastic properties.- VII. Configuration interaction and the covalent bond.- VIII. Magnetic properties of solids.- Metallic conductivity, experimental part.- I. General remarks on the conductivity of metals.- II. Methods of measurement of electrical resistance.- III. The conductivity of pure metals at normal temperatures.- IV. Temperature dependence of the conductivity of pure metals.- V. Magneto resistance effects.- VI. The effect of pressure on the resistivity.- VII. Influence of lattice defects on the resistance.- VIII. Resistivity of alloys.- Theory of electrical and thermal conductivity in metals.- I. The properties of conduction electrons in metals.- II. Statistical theory; the steady state equation.- III. Wave mechanics of the scattering of electrons.- IV. The conductivity of impure metals and alloys.- V. Thermal and electric conduction in the presence of a temperature gradient.- VI. Conduction at low temperatures.- VII. Conduction in the presence of a magnetic field.- VIII. The anomalous skin effect.- General References.- Photoconductivity.- I. Introduction.- II. Modern theories of photoconduction in crystals.- III. Photoconductivity in monatomic solids.- IV. Photoconductivity in binary compounds.- V. Photoconductivity in organic systems.- VI. A note on the photodielectric effect in solids.- VII. Some experimental techniques in photoconduction measurements.- Sachverzeichnis (Deutsch-Englisch).- Subject Index (English-German).