CH. vii.] HOT METALS 71 



The ionising power of X-rays was observed by 

 Righi soon after their discovery, and almost simul- 

 taneously by other physicists. 



The terrestrial atmosphere out of doors is usually 

 more or less ionised, and in underground air the 

 ionisation is still more marked, probably owing to 

 radio-activity in the soil. Elster and Geitel have 



TO CXECrV3OMCT-/? 



FIG. 11. 



examined this matter thoroughly, and Lenard found 

 that even the splashing of water introduced ions into 

 air, so that the atmosphere at base of a waterfall was 

 usually in some degree ionised. 



Behaviour of Hot Metals in Gases. 



Fig. 11 must stand as representative and typical 

 of a mass of important work on the ionisation and 

 disintegration of material effected by high tempera- 

 ture ; it represents the simple apparatus of Elster 



