A SCIENTIFIC CAREER 15 



very large amounts ol lead chloride, oljtained liom pitchblende as well, 

 and Paneth, assistant at the Institute, unaware of my efforrs at Man- 

 chester, made very extensive studies to achieve separation. His great 

 efforts were as abortive as mine. At my suggestion we associated in the 

 application of labelled lead. The first use of this method, early in 1913, 

 was the determination of the solubility in water of sparingly soluble 

 salts such as lead sulphide and lead chromate. We then proceeded to 

 study the electrochemistry of bismuth and lead by making use of the 

 method of radioactive indicators. We could show, among other things, 

 that Nernst's law of the dependence of the electrode potential on the 

 ionic concentration is valid even at exceedingly low concentrations. 

 Paneth then directed his interest toward the interaction of the lead ions 

 present in the surface layer of lead sulphate and the labelled lead ions 

 of the surrounding solution. I studied the interaction of the lead atoms 

 of a lead foil and also of lead peroxide with the lead ions of a solution, 

 employing labelled lead foils and non-radioactive lead salt solution, or 

 vice versa. In the last of the numerous joint investigations with Paneth, 

 we succeeded in preparing visible amounts of radium D from radium 

 emanation. By comparing the electrode potential of radium D peroxide 

 with that of lead peroxide, we were able to show that these cannot be 

 distinguished from each other. 



During my stay in Vienna, I undertook balloon ascents in the company 

 of Hess and Paneth. On one of his trips Hess took an electrometer with 

 him to follow the change in the ionization of the air with height. He 

 assumed this ionization to be due to terrestrial radiation and corres- 

 pondingly expected it to decrease with height. The opposite, however, 

 was found to be the case. With such simple means and without much 

 effort this observation led to the discovery of cosmic radiation. 



Madame Marie Curie 



When passing through Paris on the w^ay to Manchester, I never failed 

 to call on Marie Curie and I was always sure to find her amidst experi- 

 mental work. She was usually surrounded by several girl assistants 

 precipitating or crystallizing preparations. The only protection that she 

 used was finger caps of rubber. When engaged with the concentration 

 of actinium from rare-earth samples, she generously presented me with 

 an actinium preparation. I consider this specimen one of my most pre- 

 cious belongings. As the years pass by, the bottle containing the radio- 

 active sample is getting more and more coloured, indicating the many 

 years which have elapsed since I met this most remarkable personality 

 and great pioneer. 



At a later visit to the Institut de Radium, I met Joliot, who was then 

 a young assistant engaged in the study of the electrochemistry of polo- 



