McClelland and M' Henry — Uncharg^ed Nuclei. 



283 



duced separately. They quote an interesting experiment by Becker. Air 

 was filtered and exposed to Eontgen rays, and it was found that only the 

 ordinary small ions were produced in it. If the air, however, before being 

 exposed to the Eontgen rays were first exposed to ultra-violet light, 

 numerous large ions were found to be present. This leads to the conclusion 

 that the large ions are formed by the collision of the small ions with the 

 nuclei. It may be pointed out here, however, that the experiment is not 

 quite conclusive, as the large ions might be produced by the photo-electric 

 effect of the Eontgen rays on the uncharged "nuclei themselves. It is shown 

 later on in this paper that ultra-violet light, of wave-length too long to 

 ionize the air, can cause the emission of electrons from uncharged nuclei 

 driven off glass tubes by heating, and it might be argued that a similar 

 process took place in Becker's experiment. Our experiments, however, in 



APPARA TUS 



y^/^^^^^j^. 



Qutrtz 

 Tube 



\ 



To Conn 



Afvm imi/m Terrrt I'nafs 

 te induction Coil 



To Coaomete* 



f/ectro meter 



^e — 



|l|i{ IF H l[ 



Cells 



Air 



To CarTl* 



which ionization by the a-rays of uranium oxide took the place of the 

 Eontgen rays of Becker's experiment, and in which positive and negative 

 ions behaved similarly, prove conclusively that nuclei and small ions are 

 separately produced, and by their combination with each other form the 

 large ions. 



The diagram gives a plan of our apparatus. Air was drawn by means of 

 a gasometer through a cotton-wool plug, and then over a water surface or 

 through drying tubes if desired. It then passed through a long quartz tube 

 into an ionization tube containing two terminals. The first, Tj, was 60 cms. 

 long, and generally connected to earth. The second, T,, was 12 cms. long, 

 and connected to a quadrant electrometer with a capacity in parallel. 

 Between the two terminals was a glass tube which just fitted into the 

 ionization tube, and which was coated on the inside with uranium oxide. 



2 o 2 



