Poisonous or explosive gases in the atmosphere, even in minute quantities, are measured by a “long-distance” gas detector, invented by Dr. A. Herman Pfund, of the Johns Hopkins physics department. Operating automatically, it will send an electric signal to a remote-control center to warn of gases in mines, tunnels or factories, or of enemy gas attacks in time of war. It may find applications as an aid to ventilation, since it will measure the proportion of carbon dioxide in the air. The detector works along the lines of a spectroscope. Atmosphere to be tested is heated by an electric coil, and the gas is measured by a cell which also transmits the information to a galvanometer.