778 Prof. H. E. Armstrong on Low-Temperature Research 



iodine that a material having the properties of tellurium may be 

 expected to present in the light of Mendeleeff's generalization. There 

 are several places available in my scheme for lead isotopes. 



Prof. Soddy contemplates the possible rectification of the 

 accepted combining proportions through the discovery that primary 

 materials now regarded as homogeneous are in reality mixtures of 

 isotopes — as in the case of lead. I have already made a Uke sugges- 

 tion in the paper referred to above : — 



" It is perhaps not beyond the region of possibility, however, even 

 in the case of an element with so low an atomic weight (as that of 

 beryllium), that isomorphous mixtures may have passed as pure sub- 

 stances ; this possibility has not been sufficiently taken into account 

 in preparing the materials for determinations of atomic weight." 



But on general grounds and in the light of a scheme such as that 

 I have ventured to put forward, it is difficult to believe that all the 

 primaries other than isotopes have been discovered — in other words, 

 that the list of elements is practically complete and that we know 

 the possible number. Many years ago. Sir Benjamin Brodie drew 

 attention to the fact that in the case of carbon compounds certain 

 types appeared to prevail ; this may well be true of the primary 

 materials. But as in the case of radio-active substances, discovery 

 may still wait upon the evolution of suitable methods of detection and 

 a chance discovery of some highly localized material, as in the case of 

 germanium, is in no way precluded. 



(xASES OF THE ATMOSPHERE. 



Gases such as those given off from the Bath Spring are found to 

 contain helium and other rare gases in unusually large proportions. 



In the course of the examination of the rare gases derived from 

 these Springs, unidentified lines have been observed in the spectra 

 the origin of which cannot at present be explained. Astronomical 

 observation has also involved the detection of lines which cannot be 

 assigned to any known source. On these grounds continued study 

 of natural gases is desirable. The methods of separating minute 

 quantities of difficultly-condensable gases, whether by mere cooling or 

 with the aid of charcoal, have been materially improved of late and 

 specially described in the lectures given in 1914 and 1915. 



One result of the inquiry has been to show that the proportion 

 of hydrogen in the atmosphere has been much exaggerated, apparently 

 owing to the use of metal tubes in collecting and conveying the air 

 examined. 



Sir James Dewar finds less than one part of this gas in a million 

 of atmospheric air. On the other hand, he has shown that respired 

 air may contain a considerable amount of hydrogen, the amount vary- 

 ing from one person to another ; in one' case he rates the amount 



