o98 Pi'of. H. E. Armsfrom/ on Low-Tem.perature Research 



In discussing tlie problems of the atmosphere in his Friday 

 evening lecture in 1902, Sir James Dewar drew attention to the fact 

 that the proportion of hydrogen constantly present in our atmo- 

 sphere has been over-estimated and that there is not more than 

 1 /900,000th of this gas in town air that has not come in contact with 

 metal tubes. 



In connection with the problem of the distribution of the minor 

 constituents of the atmosphere, attention has been called to the con- 

 ditions which affect the recognition of the various gases and to their 

 bearing on the study of auroral discharges. The problems involving 

 experimental study in this Held are shown to be very numerous. 

 Very striking conclusions have been arrived at as to the composition 

 of the atmosphere in regions in which the temperature and pressure 

 conditions are such as could not lead to the condensation of the 

 oxygen and nitrogen. 



It is probable that above tifty-six miles the atmosphere would 

 consist substantially of the lighter gases, hydrogen and helium and 

 neon. The effect which gradual elimination of oxygen especially 

 would have on the colour of the sky has yet to be taken into account. 



Whether other gases remain to be discovered in air is at present 

 an open question : a considerable number of the lines seen in the 

 spectra obtained on passing electric discharges through samples of 

 the least condensable gases from the air are at present unidentified. 



The subject of the Upper Air and Auroras is discussed very fully 

 in Sir James Dewar's Presidential Address to the Bi'itish Association 

 at Belfast in 1902. 



Properties of Radium. 



The properties of radium have been made the subject of study 

 whenever opportunity has offered. 



The heat evolved has been measured by means of the liquid 

 oxygen and liquid hydrogen calorimeters. 



It has been shown that a Blende screen, such as Sir William 

 Crookes uses in his Spinthariscope, is not caused to scintillate by 

 radium if the screen be cooled in liquid air ; on cooling the radium, 

 however, both screen and radium being in vacuo, the scintillations 

 are as vigorous as at ordinary temperatures. This result is at once a 

 confirmation of previous observations that phosphorescent substances 

 generally lose their activity when cooled to a very low temperature 

 and a proof that radium is an entirely exceptional material. 



A series of observations of striking importance has been made 

 recently on the rate at which helium is produced from radium : these 

 not only afford a verification of Soddy and Ramsay's discovery but 

 also a most remarkable confirmation of the correctness of the theo- 

 retical predictions of Professor Rutherford. The experiments derive 

 exceptional value from the fact that they were carried out with the 



