UPON ELECTEICAL DISCHARGE PHENOMENA IN RAREFIED GASES. 
139 
rotation show the sense in which the luminous ring itself was rotating. Under 
favourable circumstances it was found that whenever the luminous ling was adjusted 
(by touching the glass at various points) to slightly envelop the wings, as indicated 
by the dotted line in the figure, a very violent rotation of the vane resulted. In this 
way it was seen that the ring rotated in the same direction as that in which a current 
would momentarily l^e induced in a coil of wire if it were suddenly moved towards a 
magnetic north pole, namely clockwise, looking through the coil at the })ole. It was 
often noticed however, that a very faintly Inminons haze hung about the ring, and 
when that, instead of the brightest portion, enveloped the mica wings, a rotation of 
the vane, also very rapid, again took place, but in the opposite direction to that 
observed in the first case. 
Distribution of Ions. 
Assuming that the path of an electrified particle rapidly moving towards a 
magnetic field is modified thereby in accordance with laws known to hold good in 
the case of the mutual action of such a field and current-carrying wires, the direction 
of rotation of the luminous ring indicated that it consisted of negative ions stream¬ 
ing inwards towards the strongest part of tlie magnetic field. 
The next question to consider therefore was the change (if any) produced in the 
distribution of the electrostatic charges upon the bulb, through tlie action of the 
magnetic field, and to observe the sign of the electrification upon the ring itself A 
piece of tinfoil fastened to the outer surface of the glass bulb invariably became 
negatively electrified when the magnetic field was suddenly created. The experiment 
was performed in the following order : Subsequently -to the passage of a strong 
discharge through the bulb, the electrification on the tinfoil patch (placed at tlie 
equator of the bulb) was tested in the usual way liy means of an electroscope. It 
was generally positive. This electrification having lieen neutralised by connection 
to earth, the current throug-h the electro-magnets was “ turned on ” while the leaves 
of the electroscope were in contact with the patch ; the tinfoil was then found to have 
suddenly acquired a strong negative electrification. 
This result appeared to be consistent with the view that, after the stimulation of 
the residual gas by the induction coil discharge, there resided upon the inner surface 
of the bulb a layer of positively electrified gas particles which, through the action of 
the magnetic field, had been removed. On the other hand, such an inrush of positive 
ions from the inner surface of the bulb towards the denser portion of the magnetic 
field, did not appear to support the idea tliat the luminous ring was negatively 
electrified, nor could it account for the direction of rotation of the ring as determined 
by the mica vane. Tliat the actual luminosity of the ring was mainly due, however, 
to the incoming radial streams of joositive ions was probable from the fact that when 
a positively electrified body was brought into contact with the glass of the bulb, a 
faintly luminous ring in the interior was greatly brightened. A pause sometimes 
T 2 
