THE DISCOVERY OF ARGON AND HELIUM. 21 



sphere, it is only present in the proportion of the i/T2oth part of 

 the original atmosphere that I took." He was very nearly correct. 

 It is a little over i/iooth. About i per cent, of the atmosphere 

 is argon, and Cavendish said it could not be more than i/i20th. 

 If Cavendish had been able to use such electric apparatus as we 

 have nowadays, and such tubes as we have, that gas would have 

 given all the spectra we now get from argon. But spectroscopy 

 was not invented until about eighty years later, by Bunsen and 

 Kirchoff. 



This diagram shows the apparatus used for the liquefaction of 

 argon. Some argon was sent to a Polish Professor, Olszewski, who 

 has worked on the Hquefaction of gases. He, by surrounding a 

 tube filled with argon with liquid oxygen made to boil in a vacuum, 

 succeeded not only in liquefying, but in soUdifying argon. Argon 

 boils at - i87°'o C, and becomes solid at - i89"^"6 C. 



This table shows the boiling points of different gases. - 246^0. 

 is the temperature at which hydrogen boils; nitrogen - 194^0. 

 HeHum is not given here because it was not discovered when this 

 table was prepared, and helium is the only gas which up to the 

 present has not been liquefied. The absolute zero temperature, 

 below which theoretically nothing can be cooled — that is to say, 

 the temperature at which we suppose any substance ceases to 

 possess any heat at all, and, therefore, cannot lose any more heat 

 — is - 273° C. Professor Olszewski has cooled helium by boiUng 

 liquid hydrogen down to - 266^ or - 267S, within a few degrees 

 of absolute zero, and yet has not liquefied it, even under pressure, 

 and therefore it probably will not be liquefied. 



Just one word in conclusion about the discovery of these gases. 

 I mentioned at the beginning that no discovery is made except by 

 hard work, and that no discovery is made suddenly. The whole 

 of our knowledge about argon and helium came from hard work, 

 and it came step by step ; one thing led to another. No one 

 would ever have thought of looking at cleveite as a mineral from 

 which helium might be discovered, unless first of all argon had 

 been discovered, and no one would have thought of argon unless 

 Lord Rayleigh, by accurate work, had found that the nitrogen that 

 came from air was a little too heavy. He would not have done 

 that unless he had been instigated to perform some rather more 



