When hydrochloric acid vapor and water vapor are allowed to diffuse together the mixture obtained is supersaturated with respect to both components. An ionizing particle passing through the mixture causes a string of droplets to form by condensation of the supersaturated vapors on the ions. Utilizing this chemical method of producing supersaturated vapors a very simple type of continuously active cloud chamber without moving parts has been developed. The cloud chamber in its present stage of development is not suitable for photographic recording but is useful for demonstration purposes. Cosmic‐ray tracks can be seen with ease by visual observation.