A PAPER by It. G. Hopkinson, of the Research Laboratories, General Electric Co., Ltd., published in the Electrical Reviewof March 1, on “Seeing at Night”, shows that valuable progress has been made on this important subject during the last few years, especially in connexion with black-out conditions. Under weak illumination, the response of the eye is quite different from that under normal conditions. So far as light is gathered by the lens of the eye and is brought to a focus upon the retina, it functions like a camera, the retina acting like a photographic plate in recording the scene for the brain to interpret. The retina is provided, however, with two separate kinds of receptor nerve cells, the ‘cones', which usually respond to bright scenes, and the ‘rods', which respond to dark scenes. In daylight the cones only function. With bright artificial light both rods and c0nes are working, the rods recording the shadows dndthe cones recording the highlights for the brain. Under black-out conditions the rods alone are functioning.