the beginning only the problem of the contact of two solid elastic bodies was solved. It was followed with the problems of local load by forces on an elastic half-plane and half-space (see Boussinesq. J.: Application des potentials. d l 'etude de l 'equiZibre et du mouvement des solides elastiques. Paris 1885). The integration then has enlarged the point contact into a surface one so as to correspond to geometry, rigidi ty or physical properties of material in the place of contact. At present days even the effect of different frictions, origin and propagation of cracks are being solved. Not only mathematics and computers but even modern experimental methods are involved in the solution of problems.