Dublin. Royal Dublin Society, June 24.—A. W. Conway: The influence of he work of Sir William Rowan Hamilton on modern mathematical hought. Hamilton's mathematical work may be divided chronologically into our groups: optics, dynamics, general, and quaternions. His work on optics is dominated by his idea of the ‘characteristic function’ and his grasp of the fact that this had application ither to a wave or to a corpuscular theory of light, representing principles of least (or greatest) time and least (or greatest) action, respectively, on the two theories. His application of the principle of varying action put the whole of dynamics on a new footing, and his methods are to-day freely used.—Phyllis Clinch: Cytological studies of potato plants affected with certain virus diseases. A histological and cytological study was made of the mosaic diseases of the potato designated simple and interveinal mosaic, crinkle, streak, and aucuba mosaic. The leaf modifications which underlie the mottling arise in part from under-development of the mesophyll, from a reduction in the number and size of the chloroplasts, and from a paler colour of the chlorophyll. In aucuba mosaic the mottling is almost entirely due to the disintegration of the chloroplasts. Intra-cellular structures of the ‘X-body’ type occur in all the diseases mentioned, except aucuba mosaic, and in the case of streak only in the early stages. This study tends to emphasise the similarity of all the potato mosaics, except aucuba mosaic, and indicates that streak belongs to the mosaic group.—W. R. G. Atkins: Radiation and life. In view of the importance of an adequate degree of illumination for most species of plant and animal life, convenient methods of measuring daylight in various sites on land and in the sea are of considerable utility. Many such measurements have been made by the author and by others using various methods, of which, for general work, the photoelectric cell is, perhaps, the most convenient. Some of the methods used and the results obtained are discussed.