THE BECQUEEEL RAYS 143 



like cathode rays, are deviable by a magnet, those of 

 polonium resemble X-rays in being unaffected. Curie, 

 on the other hand, states that both deviable and undevi- 

 able rays are emitted from radium as well as from 

 polonium, and that the non- deviable rays are stopped by 

 a piece of thin aluminium foil. None of these rays appear 

 to be polarisable, nor do they show refraction when passed 

 through a prism. 



Becquerel also discovered that air, left in contact with 

 some radio-active substances, discharges electrified bodies ; 

 indeed, it is impossible to charge an insulated conductor 

 in a room in which any such preparations have been 

 exposed. This power of inducing air to discharge electri- 

 fied bodies persists for at least a year, even although the 

 preparation has been kept in the dark all the time; it 

 cannot therefore be supposed that light-energy is in any 

 way transformed into such radiations. 



In Curie's experiments on induction it was found that 

 provided the vessel containing radium was kept vacuous, 

 the emanations had no longer the property of inducing 

 radio-activity in sheets of metal, etc., exposed in the same 

 vessel. It appears possible, therefore, to pump off the 

 radio-active matter ; and the natural conclusion is that 

 it is a gas. The gaseous matter has been collected, or at 

 least air charged with it, and it displays marked chemical 

 action, as well as high radio-activity. It converts oxygen 

 into ozone, and the glass vessels which contain it, if 

 formed of soda-glass, turn violet, and then black, owing 

 to some change. Becquerel, too, remarks on the destruc- 

 tive action of radium rays on the skin; they discolour 

 rock-salt, change yellow phosphorus to red, and destroy 

 the germinating power of mustard and cress seeds. 



On the hypothesis that the radiation of radium is 

 produced by the escape of material particles which 

 bombard the walls of the containing vessel, the velocity 



