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



Owing to the self-cooling effect exercised through surface evapor- 

 ation, drops of the Uquefied gases, even of hydrogen, are of remarkable 

 persistence. Drops of liquid air will retain this state during a fall 

 of 30 to 100 feet through the air. Even in the case of hydrogen, 

 small drops are traceable through a fall of 8 feet by the trail of frozen 

 air caused by their passage. (January 19, 1912.) 



CHEMrCAL IXTERACTIOXS AT LoW Te:\IPEEATURES. 



As Sir James Dewar has pointed out (Proc. xx, 256); perhaps 

 the most remarkable of all the low- temperature changes he has 

 discovered is the fact, mentioned in the Friday evening discourse in 

 1910, that solid oxygen at the temperature of boiling hydrogen 

 (20° abs.) is partially transformed into ozone by the impact of ultra- 

 violet rays. 



In the previous essay, in the section on " Conduction in High 

 Charcoal Vacua in relation to the Theory of Chemical Change and 

 Induction Phenomena," I have ventured to suggest that, in the 

 various cases in which the occurrence of change at very low temper- 

 atures has been observed, the conditions locally may be " spheroidaiy 



I am the more inclined to favour this explanation, in view of the 

 extraordinary behaviour of oxygen referred to above. It seems per- 

 missible to argue that if ultra-violet rays can " penetrate " the 

 molecules of oxygen and cause their disruption, they can equally well 

 penetrate a mass of either liquid or solid oxygen and cause local 

 liquefactions, so that complex systems might arise within which 

 action could take place. I question if the problem be not one of 

 those we must now hold to be beyond the range of experimental 

 inquiry ; indeed, whether the ultimate decision can well be arrived 

 at otherwise than by a purely logical process. 



The Phexomexa of Phosphorescexce. 



Luminous phenomena have always been Sir James De war's 

 favourite study from the time of his first appearance as a lecturer at 

 the Institution, when he dealt with the physiological action of light. 

 During many years, subsequently, he devoted himself almost entirely 

 to spectroscopic inquiry. Then came the period during which low- 

 temperature research all but monopolized his attention but it is clear 

 that the old interest only lay dormant. First came observations on the 

 chemical action of light, especially at low temperatures ; these were 

 followed by an inquiry into the excitation of phosphorescence by 



