The use of intermittent luminous signals in ships, lighthouses, etc., is now very general; and the common method is that of bringing a movable diaphragm before a steady source of light. Thus the light is not utilized during eclipse, and it has been estimated that in ordinary systems 65 per cent, of the light is lost (in light-houses sometimes 90 per cent.) M. Mercadier has lately proposed a new plan, the essence of which lies in varying the source of light, making it flash up to its maximum at one moment, and reducing or extinguishing it at another. This can be done either by promptly varying a supply of oxygen to a low flame, or by varying the supply of combustible gas. M. Mercadier describes an arrangement of the former kind, in which he uses a simple petroleum lamp of M. Duboscq; it has a round wick (which does not pass beyond the containing cylinder), and in the center rises a thin vertical tube, debouching a little below the plane of the wick. This tube admits the oxygen coming from a reservoir. The mode of admission is by pressure with the finger on a key, like that of a Morse apparatus; this has the effect of momentarily releasing a caoutchouc tube (by which the oxygen is conveyed) from the pressure of a clip. The flame then brightens. On taking the finger off, the supply of oxygen is stopped again, and the flame is reduced to very small size. This system, M. Mercadier says, has been adapted to apparatuses of optical telegraphy, and has given good results. He will shortly indicate how the same problem is solved with the electric light.