INTRA-ATOMIC ENERGY. 289 



many more. The latter must tlien possess great kinetic energy. If 

 an}^ cause whatever disturbs their trajectory, or if tiie rapidity of 

 their rotation becomes sufficient for the centrifugal force resulting 

 from it to overcome the attractive force that maintains them in their 

 orbit, the peripheral particles will then escape into space, folloAving a 

 tangent of the orbital curve. By this emission they will give rise to 

 phenomena of radio-activity. To attempt to briefly ex])lain why these 

 particles whirl about each other since the origin of things Avould be 

 useless. 



Whatever may be the value of this explanation, the fact of dissocia- 

 tion exists. It is very singular, surely, to see a system as stalde as 

 that of the atom l)egin to dissociate under influences so slight as a 

 ra}' of light or ver}^ simple chemical reactions, but these are facts of 

 experience before which we must bow. 



When it was thought that radio-activity was peculiar to certain 

 bodies, such as uranium and radium, it was believ^ed, and is still 

 believed b}- ph3'sicists, that the instability of these bodies was a con- 

 sequence of their high atomic weight. This explanation disappears 

 before the fact demonstrated b}^ our former researches that it is just 

 the metals of the lowest atomic weight, such as magnesium and alumi- 

 num, that become the most easily radio-active under the influence of 

 light, while, on the contrarv, those of high atomic weight, such as 

 gold, platinum, and lead, have the lowest radio-activity. Radio- 

 activity is then independent of atomic weight and is probably due, as 

 I have suggested, to certain chemical reactions of unknown nature. 

 Two bodies, not radio-active, may become so b}" com])ination. Mer- 

 cury and tin, for example, are among' the ])odies having lowest radio- 

 activity under tiie influence of light. I have shown, however, that 

 mercury becomes extraordinarily radio-active under the influence of 

 light as soon as there are added to it some traces of tin. 



This example and all similar ones will show that, as said al)ove, the 

 causes that produce dissociation of atoms aie often very slight. How 

 do they act;' Of this we are completely ignorant. Some metals that 

 become very radio-active under the influence of luminous rays, having 

 a certain wave length, lose this activity almost entirely under the influ- 

 ence of rays whose wave length is but slightly different. These facts 

 seem to have an analogy with th(^ phenomena of resonance. It is well 

 known that an organ pipe or a heavy bell mav be made to vil)rate by 

 sounding near it a note of a certain vibratory period, while the most 

 violent noises may not affect it. 



Whatever may be the causes capable of dissociating in some slight 

 degree the aggregate of condensed energy constituting the atom, 

 those causes exist, and when we know thcMU better we shall certainly 

 succeed in obtaining a more complete dissociation than we now do. 

 It was sufficient, in the present state of science, to prove its existence. 



