186 RADIATION FROM ELECTRONS [CH. xix. 



attraction, is not a function of the speed, or, in so 

 far as it is a function of the speed, it is a function 

 which diminishes as the speed increases. Accordingly 

 there must come a time when the electrical attraction 

 is incompetent to hold in the revolving mass, which 

 then begins to strain itself a little further off, with 

 the velocity now acquired ; but, by so doing, it still 

 further diminishes the force which holds it in, 

 without diminishing the centrifugal force it is itself 

 exerting ; and accordingly there is no longer equi- 

 librium. The equilibrium at the point of greatest 

 proximity is in fact unstable, and so the particle itself 

 flies off tangentially with the speed which it had then 

 acquired, thus beginning a radio-activity of a fresh 

 kind radio-activity discovered by Becquerel the 

 emission of violently flying electrons or Beta-rays. 



The whole constitution of the atom may be upset 

 by losses of this kind, and a rearrangement of its 

 substance appears occasionally to occur, with the 

 flinging away of some portion as a material pro- 

 jectile ; these particles thus thrown off constituting 

 the observed Alpha-rays. Sometimes electrons are 

 thrown off too. 



The sudden ejection of an electron, like the sudden 

 stoppage of one, is well calculated to excite those 

 vibrations in the ether discovered by Kontgen 

 known in the case of spontaneous radio-activity as 

 Gamma-rays. 



Electric Theory of Matter. 



A scheme or model for the construction of atoms 

 of different sorts of elementary substances, by means 

 of groups of electrons revolving in plane orbits round 

 a centre according to the law of direct distance, 

 together with some indication of the known spectral 



