Rays in Different Gases. 807 



this is an objection against my hypothesis. Instead, in this 

 case it happens plainly, that the virtual anode is formed at 

 the extremity of the magnetic rays, as I showed to happen, 

 and as must happen, also with air, when the intensity of the 

 magnetic field is relatively feeble. 



It cannot be thought surprising if for the moment we 

 cannot explain satisfactorily the fact, that only in some gases 

 is the induced column produced, since the mechanism of the 

 discharge is still imperfectly known, even when we neglect 

 the action of the field. We shall probably attain such 

 explanation when new experimental results have been accu- 

 mulated. But there is a research which ought to have been 

 initiated directly before formulating doubts or objections; 

 that of examining if the marked intermittency produced in 

 the discharge by the magnetic field when the tube contains 

 air (which intermittency is strictly connected with the 

 formation of the virtual anode) is produced or not with 

 those gases in which the induced column was not observed 

 by the authors. Evidently if, for any reason whatever know T n 

 or unknown, the periodicity did not exist, the want of the 

 induced column would be the natural consequence. 



Wanting still this information, the assertion : " It is 

 difficult to see why the existence of this virtual anode should, 

 depend on the gas V * is too absolute ; and so also is the 

 other one expressed by the authors in the following terms : 

 ''''That the gas used in the tube should have such an influence 

 on the nature of the magnetic rays is most difficult to explain 

 by Professor Right's hypothesis " f . 



But it is not at all difficult to understand, on the ground of 

 the following considerations, that the nature of the gas, and 

 consequently the nature of the positive ions existing in it, 

 has a notable influence on the formation of the neutral 

 systems ion-electron and on their behaviour. 



In order that an electron may be captured by a positive 

 ion and form with it one of those systems, it is necessary 

 that the relative velocity of the electron (or its absolute 

 velocity, if for simplicity the ion is considered at rest) should 

 be smaller than a certain value. In fact, in order that the 

 forces acting on the electron may be supposed reduced 

 sensibly to the electrostatic force only, it is necessary that in 

 its orbital motion round the ion, the electron remains at a 

 distance sufficiently great from it. If such condition was 

 not satisfied, the motion of the electron would be influenced 

 in a notable manner also by the electromagnetic forces due 



* L. c. p. 315. 

 t L. c. p. 313. 



