264 INTRA-ATOMIC ENERGY. 



The cathodic ra^^s are charged with electricity, yet can traverse thin 

 metallic plates connected with the earth without losing their charge. 

 Whenever they impinge upon an olistacle they immediately give rise 

 to those peculiar radiations called X rays, which differ from the 

 cathodic rays in that they are not detlected by a magnet and traverse 

 thick metallic plates capable of averting those rays, 



Cathodic rays and X ravs produce electricity upon all ))odies, 

 whether gaseous or solid, which they^ meet. They consequently ren- 

 der the air a conductor of electricity. 



By measuring the deflection of the cathodic rays by an electric field 

 and by a magnetic field, wo may estimate the velocity of the particles 



composing them, and the relation — of their charge e to their mass m. 



The velocity found oijuals a third of that of light. If ;// expresses 



the electric charge in c()uh)mt)s, we o))tain !(/ for the relation— .'^ 



In electrolysis the relation for hydrogen is ]<»', one thousand times 

 smaller. The charge e being the same, the mass of the cathodic par- 

 ticle would be one one-thousandth that of the atom of hydrogen, the 

 smallest of known atoms. The ordinary atom would then be disso- 

 ciated into 1,000 parts to form the cathodic particle. 



In place of a Crookes tube let us now use a substance spontaneously 

 ver}^ radio-active — thorium or radium, for example. We again find 

 most of the preceding phenomena with simple quantitative variations. 

 For example, we find more raj^s charged with negative electricity in 

 the Crookes tu})es than in the radium emanations which are specially 

 charged with positive electricity; but the nature of the phenomena 

 observed in the two cases appears to be identical. 



Radio-active bodies emit three diflerent kinds of radiation, which 

 may be designated }y\ the letters o', /?, and y. 



The a radiations are but slightly penetrating, are charged with 

 positiA'e electricity, and form the greatest part of the emitted rays. It 

 is under their influence that the air becomes a conductor of electricity. 

 Thev appear to be formed by the projection of particles about the 

 size of a hydrogen atom — that is to sa}', one thousand times greater 

 than the particles of the fS radiations; their velocity is about one-tenth 

 that of light. They can not be deflected except by a very powerful 

 magnet. 



The fi radiations are similar in all respects to the cathodic rays of a 

 Crookes tube. Like them they are charged with negative electricity, 



^'This relation varies according to different observers between 1.55 by 10'' and 1.84 

 by 10' (in electro-magnetic iniits). If we adopt the latter figure we see that it rep- 

 resents the enormous charge of 184 millions of coulombs per gramme of cathodic 

 matter. In electrolysis tlie charge of a gramme f)f hydrogen aiuounts to only 96,000 

 coulombs. 



