RELATIONS TO OTHER SCIENCES 147 



a charged centre : these are the Kanalstrahlen of Goldstein, an efflux 

 of positive charges toward the cathode, the electric and magnetic 

 deviations of which lead to values for the ratio of ^ varying between 

 wide limits, but always several thousand times smaller than for the 

 cathode rays. The mass of these positive centres is of the order of that 

 of the atoms. The a rays of radioactive bodies, easily absorbed, and 

 particularly easy to observe in the case of polonium and the active 

 bismuth of Marckwald, appear to be, in fact, Kanalstrahlen. The 

 mass of the positively charged particles which constitute these rays is 

 of the same order as that of the hydrogen atom, and their velocity 

 does not exceed 20,000 to 25,000 kilometers per second, so that it is 

 impossible to verify whether their mass is entirely electromagnetic 

 or not. Can we consider them as electrons as simple as the nega- 

 tive corpuscle itself, or are they of much more complex structure; 

 are they, for example, atoms or molecules which have lost a cathode 

 corpuscle? 



(37) Electrons or Atoms. On the first hypothesis, the great mass 

 of the positive centres would lead us to assign them dimensions much 

 smaller than the cathode corpuscles themselves, the electromagnetic 

 mass of an electrified sphere being inversely proportional to its radius. 

 One is thus led to the result that an electron possesses inertia, I will 

 not say weight, inversely proportional to its radius. H. A. Wilson 

 thinks to find an argument in favor of this conception of a very small 

 and consequently very inert positive electron in the observation 

 that the a rays are much less easily absorbed than the /? rays of the 

 same velocity. 



Many other reasons lead us to adopt the contrary hypothesis that 

 an a particle is very complex and little different from an atom. 

 Rutherford has given serious reasons for identifying the a particle 

 with the helium atom deprived of a cathode corpuscle; also Stark 

 gives experimental reasons referring to the emission spectra of posi- 

 tive centres in vacuum tubes, which imply a complex structure. 

 Finally the theory of the disruptive discharge attributes the produc- 

 tion of cathode rays in part at least to the impact against the cathode 

 of particles which constitute the Goldstein rays; an electron smaller 

 than the cathode particle itself seems scarcely able to produce a sur- 

 face disturbance sufficiently intense, while on the other hand, an 

 atom, unable to penetrate another atomic structure, and projected 

 with a high velocity, would produce by its impact a considerable 

 local disturbance. 



(38) The Positive charge of the a Rays. It is perhaps by this con- 

 siderable disturbance produced by the a or canal rays in matter 

 which they meet that one can explain the interesting fact that the 

 positive charge of the a rays has not been directly shown so far by 

 the negative charge which a polonium salt should spontaneously 



