CHAPTER X. 

 RADIO-ACTIVITY EVERYWHERE. 



Radio-activity is not confined to the radio-active elements. 

 It exists everywhere though in minute degree. The air of 

 cellars and caves is markedly radio-active. So is the air 

 sucked up from the soil, and particularly clay. The air 

 of the free atmosphere, normal air, is slightly radio-active. 



A wire strongly electrified and suspended in the air for a 

 few hours acquires a strong ray-emitting power which may 

 be rubbed off and transferred to leather moistened with 

 ammonia. 



Freshly fallen rain .and snow are radio-active. Air 

 bubbled through the Cambridge tap-water emits rays; so 

 does the surface water of New Haven, Connecticut, and 

 air boiled off from the mineral springs at Bath. Natural 

 carbonic acid arising from great depths of old volcanic 

 soil has been tested and found active, and so has the fine 

 mud from the mineral springs of Northern Italy and the air 

 of the Baltic coast. Everywhere over the earth there seems 

 to arise an emission of penetrating rays. For the most part 

 these rays seem to be due to the presence of small quanti- 

 ties of radium contained in the earth and permeating the 

 atmosphere with its emanation. But is it all due to this ? 

 Are we sure that all matter is not to some slight extent 

 radio-active ? Many ordinary substances certainly do show 

 radio-activity. Thus, tin-foil, glass, silver, zinc, lead, cop- 

 per, platinum and aluminum, all of them are slightly radio- 

 active. Shall we account for this on the ground that they 



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