1899.] Centenary Commemoration, 1799-1899. 217 



eistance of the pure metals is a problem of great interest. In passing 

 from the melting point of ice to the boiling point of hydrogen, 

 pure platinum loses resistance till only ^ remains, and in the case of 

 electrolytic copper the remaining resistance is only -^ T of what it was 

 at starting. Such results suggest the approach to the condition, of 

 what may be called relatively perfect electric conductivity as the zero 

 of absolute temperature is approached. 



Liquid hydrogen is a non-conductor of electricity, and as regards 

 being an insulator for currents of high potential, it is comparable to 

 that of liquid air. The properties of the liquid we have witnessed 

 in no way suggest the metallic character that chemists like Faraday, 

 Dumas and Graham anticipated ; and, for the future, hydrogen must 

 be classed with the non-metallic elements. 



The liquefaction of hydrogen has been the consequence of some 

 ten years' devotion to low temperature research. To many it may 

 seem that the results have been indeed costly in more ways than one. 

 The scientific worker who prepares the way for future development 

 in this sort of inquiry generally selects complicated methods, and is 

 attracted or diverted into many by-paths of investigation. He may 

 leave to his successors any credit that may be attached to cheapness 

 and ease of production of the agent of research — results that must 

 invariably follow. Liquid hydrogen is an agent of research which 

 will enable us to examine into the properties of matter at the lowest- 

 maintained temperature ever reached by man. Much work has still 

 to be accomplished. One of the most fascinating problems of the study 

 of low temperatures has been materially advanced. The interval 

 separating us from the zero of absolute temperature has been reduced 

 to practically one-fourth the value that it stood at when liquid air 

 was the cooling agent. We can produce in pure Helium instantaneous 

 temperatures bringing us still nearer the goal. Now we can main- 

 tain a temperature within less than 16° of this zero, and the in- 

 vestigator who will make the further attempt to reduce this distance 

 by an equivalent amount, thereby reaching a steady temperature of 

 4° or 5° absolute, will indeed face a problem of almost insuperable 

 difficulty. Well, let us take comfort in an aphorism of Davy's : 

 " Fortunately for the active and progressive nature of the human 

 mind, even experimental research is only a method of approximation 

 to truth." 



The success of the demonstration has been largely due to the 

 unremitting exertions of my chief assistant, Mr. Eobert Lennox, and 

 to the valuable aid given by Mr. J. W. Heath. 



Lord Kelvin, in moving a vote of thanks to Professor Dewar for 

 his brilliant, beautiful, and splendidly interesting lecture, said that if 

 those present wished to measure the importance of the occasion, let 

 them think what Count Eumford, or Davy, or Faraday would have 

 thought, could they have been present. They could not have hoped 

 for their scientific dreams and prophecies to be so splendidly verified 



