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



Again the subject was dealt with on June 7, 1907. The early part 

 of the lecture was devoted to an account of the difficulties met with 

 in attempting to liquefy helium, including the loss of the store of this. 

 gas laboriously accumulated over a period of two years, owing to 

 the collapse of a glass vacuum vessel and the consequent rapture of 

 the regenerator coil of the apparatus. 



On this occasion a very striking illustration was given of the 

 separation by diffusion of gases differing in density. A vacuum tube 

 containing helium and neon, showing the intense red glow of neon 

 when a discharge was passed through it, was partially immersed in 

 liquid hydrogen ; the more condensible and heavier neon at once 

 sank to the lower end, as revealed by the orange-red glow, the 

 upper part of the tube showing the yellow colour of the helium 

 discharge. This demonstration is as good an example, perhaps, as 

 could be given of the surprises Sir James Dewar has constantly 

 afforded his hearers in his lectures, by his extraordinary faculty of 

 giving apt and original illustration of points of importance on which 

 he has wished to lay emphasis. 



The lecture on the " Nadir of Temperature and Allied Problems " 

 on June 5, 1908, was again a mass of apt illustrations of low-tempera- 

 ture phenomena made manifest with the aid of highly cooled charcoaL 

 On this occasion hydrogen was solidified merely by connecting a 

 vessel containing liquid hydrogen and surrounded with liquid air with 

 an exhausted vessel containing charcoal also cooled by liquid air. 



In view of the extraordinary difficulty originally met with in 

 liquefying and solidifying hydrogen, the simplicity of the means 

 adopted in this demonstration was altogether astonishing — and 

 eminently characteristic of its author. 



The main subject considered under the title " Problems of Helium 

 and Radium" on June 11, 1909, was the amount of the former 

 generated spontaneously from radium over a given period. But the 

 phosphorescence of gases again came under discussion. 



On January 21, 1910, in a lecture on " Light Reactions at Low 

 Temperatures," after demonstrating the chemical efforts produced 

 by light, in various ways, mostly involving the exhibition anew of 

 demonstrations given in former lectures on the action of light, Sir 

 James Dewar dealt at length with the action of ultra-violet rays on 

 I)hosphorescent micro-organisms at low temperatures. 



In this lecture several light cells such as were referred to in the 

 lecture on "The Physiological Action of Light," on March 28, 187S, 

 were shown in action ; these are figured in the published abstract 

 (xix, 928). The most striking demonstration given in the lecture was 

 one showing that ozone is produced by the action of ultra-violet 

 rays on oxygen, not only when liquid oxygen is exposed to their 



