In the first part, the reflection of electrons fromcrystals is considered. We here treat this problem whenthe potential of the crystal is a completely generalthree dimensional Fourier series, whereas previouslyonly very special cases were treated. Also our methodis quite transparent while the previous methods wereobscured by involved numerical computations. Also, weshow quite generally what had been inferred from veryspecial cases, including the Bragg law, of reflection.The relation of the Fourier components of the potentialof the crystal to the optical planes is clearly shown.How the potential of the crystal is to be obtained fromthe experimental data is discussed, and a formula forthe width of the bands of total reflection is given.
In the second part the energy states of divalent crystalsare considered. The two limiting cases of weak and strongcoupling between the, two valence electrons of each atomare shown to lead to energy expressions of the sameform, and we conclude that there should be no differencein the ferromagnetism of monovalent and divalent crystalsexcept as due to differences in the constants of theenergy.
