AS OBSEEVED IN TOEEICELLIAN AND OTHEE VACDA. 
153 
terminals were used, the stratifications were visible at the first discharge ; the only expla- 
nation I can ofier is, that the stratifications may be influenced by the presence of the very 
minute points in the brass wire used in my tubes, while the new smooth platinum did 
not produce them until corroded by the discharges, 
98. When the negative terminal is of liquid mercury, whatever be the length to which 
the mercmy is elongated, its entire surface is covered with a luminous white glow ; if it is 
made positive, it is only the extreme point from which the illumination proceeds (58). 
If a tube with mercury is placed in a perpendicular position, the blue tongue is very 
large, and the surface of the mercury (which in this experiment must be made negative) 
is covered with a lambent white glow (72). This phenomenon appearing to me to be 
intimately connected with the blue-tongue discharge (68), which is always present under 
certain conditions of the stratified discharge, I determined on examining a pheno- 
menon that presented the appearance of a distinct form of discharge from that at the 
positive terminal; for this object I had several vacua-tubes constructed, in which the 
platinum, as well as brass wires hermetically sealed, were more or less protected by being 
covered with glass tubing. 
99. After many trials, I ascertained that if the negative wire is protected by glass 
tubing open at the end about one-eighth of an inch beyond the point of the wire in the 
tube, no stratifications can be observed in the discharge, which in such cases merely 
exhibits a luminous glow ; for this experiment it is necessary that the orifice in the tube 
should be contracted in order to prevent the wire being exposed, and the discharge from 
the coil should also be of moderate intensity ; as if the intensity is much reduced, 
either by the battery or by manipulation vrith the contact breaker, faint stratifications 
in the discharges may at times be observed. In a tube thus constructed, No. 90, a dis- 
charge appears to emanate from the negative wire, issuing with great intensity through 
the orifice; and if the wire and the tubing are a little inclined, the discharge will 
impinge against the side of the vacuum-tube (fig. 12), brilliantly illuminating the spot 
on which it impinges, in a similar manner to the blue-tongue discharge (68, 70); if 
this discharge is continued for a few seconds, that portion of the tube on which the 
discharge impinges will be sensibly heated ; and if a magnet is presented, the spot will 
be contracted with one pole, and with the other the discharge will be bent in a manner 
so that its extreme portion will itself impinge on the other side of the tube, illuminating 
and heating it as above. If the experiment is made by reducing the intensity of the 
discharge, so that stratifications from the positive terminal are observable, these stratifi- 
cations vanish, as the discharge, which apparently proceeds from the negative terminal, is 
forced by the magnet along the tube (fig. 13). In this experiment there is the appear- 
ance of a direction of a force emanating from the negative terminal as well as one from 
the positive, while from the latter we have, under certain conditions, as I have already 
described, a direction of force from the positive to the negative, centring to the axis of 
stratification* (57). 
* In a recent communication from Professor W. Thomson to Mr. Joule, read before the Literarj and 
MDCCCLIX. Y 
