ON August 12, the date on which Regener obtained his very high-altitude cosmic ray data, using self-recording apparatus carried by a balloon,1 measurements were made on a mountain-top in the Himalaya at an altitude of about 19,500 ft. The results of these measurements indicate clearly that the ionisation of gas in an ionisation chamber is due at least in part, if not entirely, to a secondary radiation produced in the walls of the chamber and other surrounding media, by cosmic radiation.