420 



Sir W. Crookes. 



failed to photograpli this line in products which I know contain 

 radium. The reason is my radium compound is too weak. M. 

 Demar^ay says the line is scarcely visible with a radium compound 

 only sixty times as active as uranium. My substance containing 

 radium was still weaker, judging from its action on a photographic 

 plate. 



33. The same reasoning applies to polonium. With polonium I 

 have obtained strong lines in the ultra-violet, but I can detect none of 

 them in the spectrum of my compound of UrX. All that I can see 

 are lines belonging to — 



Platinum (from the poles). 



Uranium, 



Calcium, 



Aluminium, 



and a few of the strongest air lines, besides a large number of faint lines 

 difficult to identify. 



34. Spectrum experiments having failed to show a difference between 

 radium and UrX, it was thought that possibly some information might 

 be gained by submitting them to the radiant matter test, which has 

 proved so fruitful in its application to the yttrium earths. Some 

 of the most active UrX was put in a tub© furnished with a pair 

 of terminals, and it was exhausted to a high point, heat being 

 applied during exhaustion. Simultaneously a self-luminous radium 

 compound was sealed in a vacuum tube and exhausted, heat being 

 likewise applied. When fully exhausted a strong induction spark was 

 passed through each tube. The UrX compound phosphoresced of a 

 fine blue colour. In the spectroscope no discontinuity could be seen 

 in the spectrum of the phosphorescent light. 



Under the influence of the induction spark, the radium compoimd 

 phosphoresced of a luminous rose-colour, showing in the spectroscope 

 a concentration of light in the red-orange, and a very faint citron 

 l3and, due to a trace of j^ttrium, probably an impurity. 



35. A powerful radium compound and one of UrX, each in a glass 

 cell, and a paper tray full of polonium sub-nitrate, were placed side by 

 side, and a strip of white card Avas put as a reflector at the back. In 

 front a photographic camera was arranged so as to throw full-sized 

 images of the polonium, UrX, and radium compounds on a sensitive 

 plate, and the whole was kept in total darkness for five days. On 

 development the image of the radium with the containing bottle was 

 visible, but not a trace of image from the polonium could be seen. 

 This confirms previous observations that the radiations from polonium 

 Avill not pass through glass. Those from radium and UrX easily 

 penetrate glass and other media (28). 



36. Recently claims have been put forward for the existence of a 



