I Stationary Contacts.- II Sliding Contacts.- III Electric Phenomena in Switching Contacts.- IV History.- Appendices.- § I. Hardness, strain hardening, atomic diffusion phenomena as recovery and creep.- A. Survey of the theory of plastic deformation of solid bodies and of diffusion phenomena.- B. Hardness as defined by the ball indentation test.- C. Brittle materials.- D. The work consumed by a plastic deformation.- § II. Electronic conduction in solids.- A. Energy band scheme.- B. Distribution of the electrons on the energy levels of a band, with special reference to the conduction band of a metal.- C. Potential barrier. Thermionic emission of electrons.- E. Semiconduction.- F. Potential barriers and equilibrium conditions in contacts.- § III. Tunnel effect. Thermionic emission and field emission.- A. Theoretical basis for the calculations. Classes I and II of calculation procedure.- C. Tunnel resistivity.- D. Comparison between tunnel current and thermionic current according to formula (III,13).- E. Tunnel effect when both electrodes are of the same semi-conducting material.- F. Remark concerning the field strength.- § IV. Structure, electric and thermal conductivity of carbons.- A. Introduction. Graphite latice.- B. Carbon grades.- C. Graphitization.- D. Electric conductivity of carbons.- E. Heat conductivity of carbons.- § V. Hydrodynamic or thick film lubrication.- § VI. Remarks about threadlike metallic formations.- § VII. Some fundamental formulas concerning the electric discharge.- A. Introduction. Kinetic fundamentals.- B. Drift velocity.- C. Thermal ionization. Saha's equation.- D. Plasma.- E. Current in vacuum restricted by the space charge of the current carriers.- § VIII. General theory of the arc that appears in relays.- A. Introduction.- B.Reminder of elements of the theory of electric discharges in gases.- C. Thickness of the cathode layer and metal vapor pressure within it.- D. Definition of the examples.- G. Comparison with measurements.- H. Power balance at the cathode.- I. Summary of the results concerning cathode phenomena in arcs between non-refractory electrodes.- J. The power balance at the anode.- K. Cathode of refractory materials as carbon and wolfram.- L. Why is the voltage of a short arc of the order of 10 V?.- M. Movement of the arc spot.- N. Current-voltage characteristics of arcs. Arc life.- § X.- § XI.- Author and literature index.