The object of this paper is to present in a systematic way a general method to determine whole fields of displacements and of their space and time derivatives. The method can be called physical, or experimental, in the sense that the body itself, rather than mathematical models, gives the required information. The method can be called geometric in the sense that it consists in the drawing, or photographing, sets of lines on the planes of interest. The method in principle is applicable to high and low modulus materials, to infinitesimal and finite strain, to static and dynamic, elastic and plastic problems. If the bodies are transparent, it gives information inside the bodies also. The method also has educational value in that it follows step by step the classic development of the theory of continua and permits the visualization of the results obtained at each step of the development. The description of the method is given and illustrative applications are shown.

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