A SCIENTIFIC CAREER 13 



Years with Rutherford 



The physics laboratory of the University of Manchester was housed in 

 a spacious building. The chief equipment of the institute was electro- 

 scopes built with cocoa cans, sealing wax, sulphur rods, gold leaves, and 

 reading microscopes. Once adjusted, the electroscopes were not permitted 

 to be cleaned, and the smokey atmosphere of Manchester left its visible 

 marks all over the laboratory. The years I had the privilege to spend 

 in Rutherford's laboratory in Manchester, between 1911 and 1914, 

 witnessed some of the greatest discoveries in the history of physics. 

 I could follow from close quarters the discovery of the atomic nucleus and 

 how Rutherford devised, carried out, and interpreted the results of ex- 

 periments. All this was done with the greatest ease, without visible effort. 



Niels Bohr came to Manchester in 1912. He recently remarked in 

 an after-dinner speech that I was the first-one he met when he entered 

 Rutherford's institute. Rutherford— and not he alone— soon realized 

 Bohr's genius. When I was enjoying Rutherford's hospitality one Sun- 

 day afternoon, soon after the discovery of the atomic nucleus, I happened 

 to ask him about the origin of/3-rays. Thea-rays clearly originated from 

 the nucleus, but what about the origin of /9-rays ? Rutherford answered 

 promptly, "Ask Bohr", and the answer was at once given by the latter, 

 emphasizing the difference between nuclear and non-nuclear ^-particles. 

 Bohr was however not always easy to understand. When he briefly stated, 

 "Argon is not the right argon", he made a statement that was at that 

 date not easy to interpret. It was then, in 1912, already clear to him 

 that it is not the mass number but the atomic number that is decisive 

 for the place of an element in the periodic system. Soon after, this fact 

 was decisively brought out by Moseley's work. I consider myself lucky 

 to have had the opportunity to help Moseley set up the first X-ray 

 spectrograph. We turned to the steward of the chemistry department, 

 Mr. Edwards, who handed us a beautiful, very large potassium ferri- 

 cyanide crystal which found application in Moseley's spectrograph. A mag- 

 netic device served to bring small metal disks covered with the element 

 to be investigated into the electron beam, which had to excite the X-rays. 

 Moseley's fundamental work brought out, among other things, that, 

 while the atomic weight of argon is higher than that of potassium, its 

 atomic number is not— that "argon is not the right argon", as stated by 

 Bohr previously. Moseley has also shown that the anomaly of the posi- 

 tions of tellurium and iodine in the periodic system disappears if we 

 consider the atomic number instead of the atomic weight. 



When I arrived at Manchester, Rutherford wished me to study the 

 solubility of actinium emanation in various liquids. It was not an easy 

 task in view of the short life of this emanation, now called actinon, the 

 half-life of which is four seconds only. This was, however, a very good 



