In 1938 the German physicist Walter Heitler, who had escaped Germany as a scientific refugee to live and work in England, was at Bristol University researching a number of theoretical topics, including the formation of cosmic ray showers. He mentioned to Cecil Powell, at that time considering the use of cloud chambers for cosmic ray detection, that in 1937 the two Viennese physicists, Blau and Wambacher, had exposed photographic emulsions in the Austrian Alps and had seen the tracks of low energy protons as well as 'stars' or nuclear disintegrations caused by cosmic rays.