at the Royal Institution, 1908-1916 759 



(*' Gases at the Beginning and End of the Century "). In the latter 

 part of the lecture, vacuum vessels were again referred to specially 

 and various types shown. 



The most important matter touched on in this discourse was the 

 method of separating the more volatile constituents of air which 

 has since been of great service in preparing neon. 



" The Problems of the Atmosphere," discussed in the lecture on 

 April 11, 1902, were mainly those relating to gases of low density 

 present in minute proportions in ordinary air — such as hydrogen and 

 helium — and to the probable increase in the amount of these as the 

 atmosphere is ascended. A method was described of liquefying air 

 and at the s'ame time separating the more volatile gases, without the 

 use of liquid hydrogen, uncontaminated by compression pumps. 

 Reference is briefly made to this lecture in my previous essay. 



The ever-perennial subject of " Low Temperature Investigation " 

 again came under notice on January 16, 1903. The work described 

 in this lecture is discussed in the section on " Modifications in the 

 Properties of Matter at Low Temperatures," in my previous essay. 

 Perhaps the most striking case brought forward was that of india- 

 rubber, which at very low temperatures becomes a rigid, resilient, 

 brittle solid through which oxygen does not diffuse. 



" Liquid Hydrogen Calorimetry," the subject of the lecture on 

 March 25, 1904, also has been discussed in my previous essay. 



The lecture on " New Low Temperature Phenomena," on 

 January 20, 1905, was the first of a series dealing with Sir James 

 Dewar's momentous discovery of the extraordinary absorptive power 

 of charcoal at low temperatures. That the discovery was not made at 

 an earlier date, as soon as liquid air became available as a cooling- 

 agent (1892), may appear remarkable, but the frequency with which 

 the obvious has remained unseen is well known. Sir James appears 

 to have had his attention diverted mainly by the extraordinary reduc- 

 tion of chemical action at low temperatures — through finding that 

 substances such as phosphorus and potassium could not be oxidized, 

 and that no action was traceable even through the agency of electric 

 currents. He was thus led to suppose that physical action would be 

 similarly affected, the more as in his earlier work on hydrogenenium 

 he had found that the absorption of hydrogen by finely-divided 

 palladium was not promoted by cooling. 



The subject was further developed on June 8, 1906. The use of 

 charcoal in rendering possible the use of metallic vessels as perfect 

 vacuum flasks was first disclosed in this lecture. 



