142 SIR WILLIAM RAMSAY 



anxiety on the part of the candidate to show that he or 

 she knew all about argon. 



The actual state of knowledge concerning the new 

 gases in 1897 will best be described in Ramsay's own 

 words, and fortunately an excellent summary is given 

 at the end of a paper which he communicated to the 

 Annales de Ckimie et de Physique and which appeared 

 in April 1898. The following is a slightly abbreviated 

 translation of this summary : 



" Without attempting to mention the numerous theories and 

 hypotheses which have been published with reference to argon 

 and helium, we will confine ourselves to positive facts. 



The densities of helium and argon are respectively 1'98 and 

 19'94. The relation between the specific heats at constant 

 volume and constant pressure for each gas is 1*65. This relation 

 can only be consistent with the simplest molecular structure. 

 The molecules must be incapable of motion of any kind except 

 that in virtue of which they traverse space. If there is any 

 other kind of motion, it can only be exceedingly small. The 

 imaginary atoms of Boscovich could alone strictly comply with 

 this condition, and since these gases give well-defined spectra 

 it follows that they are not entirely without internal movement. 

 All that can be stated therefore is that the vibration which 

 produces the spectrum cannot be considerable enough to have 

 an appreciable influence on the ratio of their specific heats. 



We may recall the fact that mercury, an element which for 

 other reasons is regarded as mono-atomic, exhibits the same 

 relation. It seems that the conclusion is inevitable that the 

 molecules of helium and argon are each formed of one atom. 

 Hence it follows that the atomic weight is double the density 

 or 3*96 for helium and 39 '88 for argon. 



If these gases, however, are not homogeneous, if they consist 



