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A crystal which has absorbed a light quantum can be treated either as an assembly of molecules or else as a giant molecule. If the exchange of excitation energy between crystal cells is slow as compared to the periods of vibration, the first description is preferable; if it is fast, the second picture is better. Both cases are discussed in connection with the following question: To what extent can excitation energy absorbed by an arbitrary cell of the crystal be used photochemically at a specific point which may be far removed from the absorbing cell? The results are applied to the behavior of polymerized pseudoisocyanines, to the hypothetical photosynthetic unit and to the theory of sensitized photographic plates.

The nature of small ions in electrolytic (e.g., aqueous) solutions is discussed in terms of the configuration of the adjoining polarized medium, and the role of this configuration in electronic transitions involving one or a pair of ions is treated in a general way. Light absorption by a single iorl is shown to depend critically on this configuration; a theory developed previously by the authors is reviewed, and future possibilities of exploring the nature of the configuration by investigation of such spectra are explained. ]Electronic transitions, such as an "electron transfer" process, during binary collisions of ions are treated, and a general method is developed, based upon DEBYE'S "diffusion" theory for ion collision rates and a nonadiabatic type of potential curve. Rates of chemical processes are found to depend decisively on the interaction of two ions at separations where the simple coulomb law is not valid.* Wir haben diese Arbeit als Beitrag fiir das meinem Freunde 1ROB~t~T POltL anl~iBlich seines 70. Geburtstages gewidmete Heft gewiiblt, da sie i)berlegungen fiber negative elektrolytische Ionen enth~lt, die sehr nahe verwandt sind mit den Deutungen der PO~ILschen Farbzentren in Kris~callen. Da die Arbeit in eine Reihe yon Artikeln gehd~, die Herr PLATZ~IAN fiber dies Gebiet welter zu verdffentlichen gedenkt, so ist sic englisch gesehrieben; iiberdies ist Prof. PLATZMANs Beitrag bedeutsamer ftir ihr Zustandekommen als der meine.J. FRANC~.