 Here (Heisenberg 1930: 16), it is assumed that the electron is illuminated by light of wavelength \(\lambda\) and that the scattered light enters a microscope with aperture angle \(\varepsilon\). According to the laws of classical optics, the accuracy of the microscope depends on both the wave length and the aperture angle; Abbe’s criterium for its “resolving power”, i.e., the size of the smallest discernable details, gives   