AS OBSEEVED IN TOEEICELLIAN AND OTHEE VACUA. 
141 
If the south pole be presented the discharge will be contracted, impinging on and 
brilliantly illuminating the portion of the tube round the negative wire. 
69. In the apparatus* (Plate IX. fig. 7 of my last paper), when one wire is positive 
and the mercury negative, if the vibrating hammer of the induction coil be pressed by 
the finger so as to ensm’e a sudden disruption, the redness on the surface of the mercury 
instantly disappears, an intense white glow being substituted, while the dark band is 
nearly fiUed with stratifications. On carefully examining the discharge when in this 
state, it will be observed that on pressing the contact-breaker so as to ensure a more 
sudden disruption, the stratifications which now fill the space previously occupied by 
the dark band appear also to emanate from the surface of the mercury. If a portion 
of air awgw of the capacity of the tube be introduced, the stratifications assume a reddish 
tinge, and this redness increases as air is added, the redness on the surface of the 
mercury disappearing; if the discharges are taken from wire to wire on the intro- 
duction of a minute quantity of air, the negative wire loses its red glow and becomes 
intensely blue. 
70. I have alluded to a remarkable phosphorescent blue tongue discharge from the 
negative wire (68), and stated that this discharge is strongly affected by the magnet. 
While experimenting with many of the vacuum-tubes, I observed that this peculiar 
form of the discharge was always more distinct when the stratifications assumed the 
cloud-hke appearance already described. When the stratifications are narrow and close 
this blue discharge is scarcely visible, although traces of it can sometimes be brought 
out by a magnet. In vacua which show narrow stratifications, fluorescence pervades the 
tube equally in all parts ; but when the stratifications assume the cloud in a distinct 
form, the fluorescence is almost entirely conflned to the portion of the tube near the 
negative wire. In my fii’st experiments it appeared doubtful whether this blue tongue 
discharge might not be due to the reflexion on the sides of the glass, from the white- 
tongue discharge already described ; but the result of many experiments made under a 
variety of conditions, lead me to the conclusion that it is a distinct phenomenon, having 
the appearance of being due to a force or action emanating from the negative terminal. 
71. In one tube (Hyd. Merc. Vacuum, No. 47) the white tongue was peculiarly di- 
stinct, and the blue very brilliant and clear : in this tube the stratifications were much 
separated, exhibiting the large and long clouds from the positive terminal, to within 
four inches of the negative. The phosphorescence in the glass did not appear in any 
part except close to the negative wire, where it was very brilliant, illuminating that 
end of the tube with a deep blue colour. If during the discharges a horseshoe magnet 
is placed under the negative wire, the stratifications are brought down towards the 
magnet, and the white tongue is strongly deflected ; on moving the magnet across the 
tube, the tongue is attracted or repelled according to the pole which is presented ; while 
the blue discharge around the negative, although attracted and repelled, is so, compara- 
tively with the white, in a far less degree. 
* Philosophical Transactions, 1858, Part I. PL I. fig. 7. 
