174 SUMMARY OF ELECTRON THEORY [CH. xvm. 



the emission of energy as '36 million ergs per second. 

 Combining this with the magnetic deflexion, the 

 result is that u = 2'6xlO Q centimetres per second, 

 while e/m = 6,500 electro-magnetic units. 



Des Coudres, using both electric and magnetic 

 deflexion, but employing more complex rays, obtained 

 u=l'65 x 10 9 , and e/m 6,400. 



Activity of Radium at all Temperatures. 



Messrs. Dewar and Curie have shown that at the 

 temperature of liquid hydrogen, 252 degrees below 

 zero centigrade, the heat evolution of radium is the 

 same as at ordinary temperatures. It has also been 

 shown to be equally active in the solid or in the 

 dissolved state, and elevation of temperature makes 

 it no more active. 



The activity of radium, as observed in Crookes' 

 spinthariscope, is just as marked at the temperature 

 of liquid hydrogen as at ordinary temperatures, 

 provided the luminescent screen is not likewise 

 chilled. 



Spectrum of Radium. 



In speaking of the spectrum of radium there is an 

 ambiguity to be guarded against. We may mean 

 the spectrum of radium itself, when it is put in a 

 flame or subjected to the electric spark ; or we may 

 mean the spectrum of the spontaneous glow of 

 radium chloride or bromide, which can be seen in 

 the dark. The latter spectrum is very difficult to 

 observe, because of its extreme faintness, but the 

 experience of Sir William and Lady Huggins has 

 enabled them to examine it, and to show that it 

 is chiefly the spectrum of atmospheric nitrogen ; 

 which is thereby proved to be ionised and violently 



