  Mie’s theory of matter is akin to the traditional geometric view of matter: matter is passive and pure extension. Weyl (1921b) remarks that he adopted the  standpoint of the classical pure field theory of matter in the first  three editions of Weyl (1923b) because of its beauty and unity, but  then gave it up. Weyl (1931a) points out in the Rouse Ball Lecture  that since the theory of general relativity geometrized a physical  entity, the gravitational field, it was natural to try to  geometrize the whole of physics. Prior to the advent of  quantum physics one was justified in regarding gravitation and  electromagnetism as the only basic entities of nature and to seek  their unification by geometrizing both. One could hope, following the example of Gustav Mie, to construct elementary material particles as  knots of energy in the gravitational-electromagnetic field,  that is, tiny demarcated regions in which the field magnitudes attain very high values. 