THE METHOD OF POSITIVE RAYS 53 J 



3. It must not be decomposed by long-continued exposure to the 

 electric discharge. 



These are properties which a priori we should hardly have expected 

 an allotropic modification of hydrogen to possess. 



Mendeleef predicted the existence of an element with an atomic 

 weight 3. According to him this element should be intensly electro- 

 negative and possess the properties of fluorine to an exaggerated extent. 

 The gas X 3 can, however, be kept in glass vessels, which we should not 

 expect to be possible if it possessed more than fluorine's power of com- 

 bining with glass. I prefer to defer expressing any opinion as to the 

 actual nature of the gas until I have had the opportunity of making 

 further experiments upon it. It is only about two months ago that I 

 found how to get the gas with any certainty, and, as the method in- 

 volves long bombardments, each experiment takes a considerable time. 

 This has prevented me from making several experiments which suggest 

 themselves, and which ought to be made before coming to a final de- 

 cision. I thought, however, that the investigation, though incomplete, 

 might not be unsuitable for a Friday evening discourse, as the gas, 

 whatever its nature, is certainly one of considerable interest, and its 

 detection illustrates the delicacy of this new method. 



