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CUCUMBER mosaic viruses 3 and 4 of Ainsworth1 have many properties in common with tobacco mosaic virus, in spite of the fact that they do not cause disease when inoculated to tobacco plants. They are sufficiently stable so that their virus proteins have been isolated chemically2 ; these proteins resemble the tobacco mosaic virus protein in optical characteristics when in solution, in high inactivation temperatures, in the X-ray diffraction patterns3 they produce, and in serological reactions. We have carried through ultracentrifugal isolations of the cucumber virus proteins and have found that they are also like tobacco mosaic virus protein in sedimentation rates.

WE are in complete agreement with Barrett and Mansell1 concerning the absorption spectrum of water down to 185 mµ, and also in their implied criticism of the work of Golding2. Independently of Barrett and Mansell, we had failed to observe with a Unicam SP.500, flushed with nitrogen, the fine-structure described by Golding, and the results were therefore checked on a vacuum grating spectrophotometer3 and extended down to 180 mµ using silica cells of 1 cm. and 1 mm. path-length. Plotted as log A against wave-length, the absorbance of water rises nearly linearly down to at least 180 mµ, with no trace of fine-structure. At about 20° C. the absorbance values for 1 cm. path-length were found to be 0.1 at 192 mµ., 1.0 at 186 mµ and 10 at 181 mµ very nearly. More complete and precise results will be published elsewhere.

THE recent development of our knowledge of the electronic structures of molecules makes it possible to specify with reasonable certainty the particular electron with which a definite molecular ionization potential is to be associated. In an organic molecule the variation of an ionization potential with, for example, alkyl or halogen substitution reflects the change in negative charge density in that part of the molecule in which the electron is located. The existence of resonance in a molecule also considerably affects the ionization potentials of the resonating electrons. It is clear, too, that ionization potentials are intimately bound up with chemical activity, dipole moments, refractivities, combination radii, electronegativities, etc.

WE have recently been investigating the far ultra-violet absorption spectra of a number of organic compounds of the type R1COOR2; R being an alkyl group or a hydrogen atom. It has been found that only the simplest of these, namely formic acid, shows discrete absorption bands in the region 2000–1000 A. The interpretation of the electronic structure of the carboxyl group will therefore depend to a considerable extent upon the analysis of these discrete bands.

EVAPORATION of aqueous solutions of purified plant viruses on the collodion-covered screens used for electron microscopy leaves many of their elementary particles in a regular array1. With very dilute solutions this regularity is largely two-dimensional, but more concentrated solutions sometimes furnish the kind of three-dimensional order characteristic of a true crystal. Such regularity has been imperfect when these crystalline masses were thin ; and clear electron micrographs have not been produced from thicker masses, or from single crystals, because of the diffuse electron scattering by their underlying molecular layers.

THE first International Conference on Photo-luminescence, which was held at Warsaw in May last year, was presided over by Prof. P. Pringsheim and attended by many eminent European physicists. It served to bring to the forefront the important scientific results which the subject is at present yielding. Some twenty-seven papers on the various aspects of phosphorescence and fluorescence were presented. They have now been published by the Polish Physical Society in the volume under notice. Rapports sur la photoluminescence presentes a la reunion Internationale de Photoluminescence, Varsovie, 20–25 Mai 1936 Publies par la Societe Polonaise de Physique sous la redaction de Prof. Dr. S. Piekowski et Dr. W. Kapuciiski. (Vol. 5 des Acta Physica Polonica.) Pp. ix + 431. (Wilno: Acta Physica Polonica, 1936.)