272 INTRA-ATOMIC ENERGY. 



Durino- iiuiny years physicists luive held that the particles emitted 

 in the phenomena of radio-activity were merely fragments of atoms, 

 doubtless charued with electricit}', but nevertheless always formed of 

 matter. 



This opinion might seem to be contirmed by the fact that radio- 

 active emissions are often accompanied l)y a projection of material 

 particles. In a Crookes tul)e the emission of solid particles from the 

 cathode is so considerable that they metallize plates exposed to their 

 projection. 



Similar deportation of matter is likewise observed in most elective 

 phenomena, notably when electricity having a sufficiently high poten- 

 tial passes })etween two electrodes. The spectrum of the electric sparks 

 then formed always shows the lines characteristic of the metals of 

 which the electrodes are formed. After repeated dischai'ges ])etween 

 a l)all of gold and one of silver, we find silver on the gold ])all and gold 

 on the silver one. With currents of high frequency Monsieur Oudin 

 showed that electrodes of amalgamated gold, used in air having the 

 ordinary pressure, lose nearly one-tenth of a milligram of their 

 weight per hour. In these various cases matter is doubtless carried 

 away by the velocity of the electric molecules, as is the sand of the 

 sea })y the violence of the waves. 



Still another reason seemed to clearly prove the materialitj* of the 

 cathodic emissions. They can be deflected ])y the magnetic field; 

 besides, they are charged with electricity, and as electricity had not 

 been known to l^e transported without material support it was neces- 

 sary to pr(^suppose the existence of such a support: It is true that, 

 in the theory of electrons, it is admitted that the electric atom in 

 motion, wholl}^ free from all matter, behaves exactly like a current 

 and can be deflected by a magnet; l)ut some 3^ears ago that theory, 

 unsupported by the discovery since made by Zeemann, had not the 

 considerable extension it has to-day. 



The kind of matter-dust supposed to form the emissions from the 

 cathode and from radio-active bodies showed very singular charac- 

 teristics for a material substance. According to the experiments of 

 J. J. Thomson, the products of this emission were identical, no matter 

 what might be the body dissociated. The electric charge and the 

 mass being always the same, it was necessary to admit that in different 

 bodies identical elements were found. 



These supposed material elements had likewise lost all the properties 

 of the matter that gave them birth. Lenard showed this clearly when 

 he sought to verify one of the ancient hypotheses, according to which 

 the effluvia generated by ultra-violet light impinging upon metals are 

 composed of dust torn from the surface of metals. Taking a body — 

 sodium — easily dissociated ])}" light, and which can also be detected in 

 intiuitesimal quantities in air by means of the spectroscope, he found 



