[Letters to the Editor]

Abstract

WE had the privilege of hearing of his results from Dr. Penrose shortly after his discovery of the hyperfine structure of paramagnetic resonance, and of discussing them with him when he was on a visit to Oxford. We were stimulated to make some calculations on the effect, in particular its variation with orientation of the applied field, and kept up a correspondence with him on this subject, which was interrupted by his death. The variation observed by Penrose differs markedly from the expected variation calculated by us on the basis of Polder's theory, and we believe that the discrepancy indicates an influence of the crystalline electric field on paramagnetic ions more complicated than has been generally assumed. Penrose's work, therefore, opens a new and fruitful approach to the study of paramagnetism.