806 Prof. A. Righi on Magnetic 



substituted certain other gases for the air in my discharge- 

 tubes. But in my opinion that does not at all constitute an 

 objection against my explanation ; it would show only the 

 necessity for completing the fundamental hypothesis, or at 

 least for finding the reason why in certain gases the formation 

 of the virtual anode does not take place to a perceptible 

 degree. 



Considering also that in air the magnetic rays are produced 

 only in certain conditions of experiment, and particularly 

 with a given tube only between certain limits of the pressure 

 of the air, of the intensity of the field, and of the intensity of 

 the discharge current, before asserting that in some gases the 

 virtual anode does not exist, it was needful for the authors 

 to vary these factors. As unfortunately they do not give 

 numerical values, there remains the possibility that the 

 absence of the virtual anode is due only to their not having 

 combined rightly the conditions required for its production. 



However, I admit willingly the facts asserted, which appear 

 to me very interesting from the circumstance that, according 

 to the authors, mixtures of nitrogen with one of the three 

 gases, oxygen, hydrogen, and carbon dioxide, act in the same 

 manner as air, while the induced column is absent with the 

 natural illuminating gas (first experimented with by them), 

 and also with the pure gases above mentioned. In effect this 

 singularity of nitrogen could be paralleled by another one 

 presented by the same gas, which is almost the only one 

 (carbon monoxide shows less markedly the same behaviour) 

 in which the phenomenon of the globular discharge, already 

 described and studied by me, is produced. 



Speaking of the virtual anode I must also remark, that the 

 authors have given to one of the facts observed by them 

 (which coincides with one already described by me, though 

 this appears to have escaped their attention) a not rigorous 

 interpretation. In certain gases they observed the production 

 of the induced column, but of small length, and besides 

 ascertained that it was always bent in the same sense 

 (showing that it was due to a positive current directed from 

 the extremity of the magnetic rays to the bottom of the 

 discharge-tube), whatever the region of the column to which 

 the lateral magnetic pole was approached. From that the 

 authors rightly infer, that in such a case the virtual anode 

 with a positive current directed in the two senses does not exist *: 

 but the way in which this conclusion is presented might lead 

 to the inference that the anode does not exist at all, and that 



* L. c. p. 314. 



