Discharge of Electricity through Gases. 337 



fore not be one of equilibrium, but a compromise between the con- 

 tinuous rotation which the magnet tends to set up and the tendency 

 to choose the path of least resistance. There is a real difference 

 between this view and that generally brought forward; for, if I am 

 correct, we should have in the final stage, which to us seems to be one 

 of equilibrium, the particles of the gas carried through the current in 

 a direction at right angles to it. 



I think that I may quote the experiments of De la Rive on the 

 rotation of a current round a magnet in support of what I have said. 

 I have repeated his experiments by using a vessel very similar to 

 those previously described : the inner cylinder contained the pole 

 piece of a strong magnet, and was not used as electrode. One of the 

 electrodes was a ring surrounding the axis ; the other, a wire in the 

 direction of the axis of the magnet. It has already been pointed out 

 by De la Rive that the experiment is not successful with air ; there 

 seems a tendency towards rotation, but no ^rotation. Here, then, the 

 preponderance of conductivity of the particles which have already 

 carried the discharge does not seem sufficient to rotate the current ; 

 yet we cannot imagine that, for the same intensity of current, the 

 effect of the magnet should not be the same. We must conclude, 

 therefore, that here the particles are driven through the current, but 

 do not carry the current with them. Even with vapours like alcohol, 

 with which a continuous rotation can be ^obtained, it often happens 

 that the current rotates only through a small angle, then suddenly 

 jumps back into its original lines, and then tries to go round for some 

 time, until it finally succeeds. Those who are familiar with the 

 experiments of Pliicker will find, I think, that they can easily be 

 explained by what I have said, but that in no case can the form in 

 which the discharge takes place be one of equilibrium ; nor is it even 

 & circle, which is the curve in which a flexible wire carrying the 

 current would set if it was fixed at both ends. 



As far as the effect of the magnet on the negative glow is con- 

 cerned, it is generally considered sufficient to say that it sets in 

 magnetic lines of force, or sometimes that it winds itself in spirals 

 round those lines. The facts are true, and easily explained by any 

 theory of projection, but they do not contain the whole truth. 



In order to understand fully the action of the magnet, we have to 

 be careful in distinguishing two totally distinct questions. The first 

 question is this : In what way does the magnet affect the rays of the 

 glow which start from any given part of the negative electrode ? This 

 question has been satisfactorily answered by means of the theory of 

 projection. Tho second question, which has not received sufficient 

 attention, is this : At what parts of a negative electrode placed in 

 magnetic field does the glow form itself? For we find that large 

 parts of a kathode sometimes remain absolutely dark in a magnetic 



