Paul Gruner, Elementary geometric representation of the formulas of the special theory of relativity
“ Posing , we immediately find that the coordinates of a point satisfy the requirements of the theory of relativity: With this mode of representation which contains no imaginary quantity, it is easy and simple to graphically demonstrate the different results of the theory of relativity (length contraction, dilatation of clocks, change in mass, energy, volume, etc. ) . ”
