UPON ELECTPvICAL DISCHARGE PHENOMENA IN RAREFIED GASES. 
14 !) 
negative concentration until the potential is such that they suddenly flow Inwards, 
Avhile the superficial layers of the negatively charged gas-mass at the centre of the 
bulb move rapidly outward. In this manner is explained the occasional apj^earance 
of a ring of green fluorescence upon the equator of the bulb at the moment tlie 
electrodes are magnetised, and also the loss of positive electrification, not only from 
the walls of the bulb hut from objects placed in the interior as well. The similarity 
between both the diselectrification effects and the luminous ring phenomena has been 
also experimentally demonstrated, and it now remains to ofler an ex})lanation of the 
luminous ring itself. The final action of the magnetic field, the incoming streams of 
positive ions, and the production of the luminous ring, are represented l)y fig. 12. 
The ring is most luminous at its outer edge or surface owing to that being tlie 
boundary at which most of the incoming positive and outgoing negative ions collide. 
But while the concentration of negative ions can be explained for a growing magnetic 
field, it is not clear why the sudden cessation of the field should also produce a con¬ 
centration. The influence of the rate of change of the magnetic lines was moi’e 
marked in this than in the former case. AVliether Mr. AYalker’s ingenious theoryf 
of the luminous ring satisfactorily explains that result is not quite certain. I could 
get no direct experimental proof either one way or the other. The direction in 
which the luminous rino- rotates has been already referred to in detail. It must now 
O xJ 
he pointed out that the sense is opposite to that in which a negative ion might he 
expected to move owing to the sudden growth of the magnetic field. On the other 
hand, it is evident that the outer surface of the ling is more positive than the 
surrounding negatively electrified gas particles, which would in consequence flow 
inwards and be deviated in a manner consistent with the observed direction of rota¬ 
tion of the whole. It is seen also that the positive ions felt the action of the 
magnetic field to a lesser degree, probably owing t(.) their greater mass and 
comparative want of mobility. AA^e have, tlierefore, to imagine the initial cloud of 
concentrated negative ions not necessarily in rotation, but that, owing to the incoming 
streams of positively electrified particles, the gas-mass at the centre of the bulb 
* ‘Rroc. Roy. Institution,’ vol. ‘J, p. 142. 
t ‘Electrician,’ August 25, 1899, p. 634. 
