180 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
(C.) 0 '042430 W, 16 luminosities resembling closely fig. 6, Plate 15, when 
700,000ohms resistance was introduced in the circuit, (C.) 0*008322 W, 3arrow- 
headed luminosities were produced, each 4 inches long, the first adhering to 
the straight wire, positive, 45, fig. 45. 
40. — Pressure 6'6 m.m., 8684 M, 8040 cells. 19 luminosities something like 
the fifth and sixth luminosities from the positive in fig. 7, Plate 15. The 
F and C lines were seen with the spectroscope, especially in the glow around 
the negative. 
41. — Pressure 5'6 m.m., 7368 M, 4800 cells. 12 luminosities like fig. 6, Plate 15. 
42. — Pressure 3'9 m.m., 5132 M, 4800 cells, 200,000 ohms resistance, 
(C.) 0'012420 W. 10 luminosities, part of one of which is depicted 
on the left of 49, fig. 45. From time to time there arose in the centre 
of the tube a concave spindle-like formation, 49, fig. 45, which gradually 
extended itself to both poles, and absorbed all the luminosities. Examined 
with the spectroscope the C and F lines were brilliantly seen in the glow 
around the negative terminal, but were not visible in the spectrum of the 
nebulosities, notwithstanding that they were brighter than the negative 
glow ; there were blue, green, and red visible, but not the characteristic green 
and red lines of hydrogen. 
43. — Pressure 3'1 m.m., 4079 M, 4800 cells, (G.) 0'024970 W. A very 
curious phenomenon was presented, which has repeated itself on several 
occasions ; at first the plane of the strata cut the tube at right angles, 
the strata being perfectly steady. An agitation was afterwards visible, 
and the strata arranged themselves diagonally as in 52, fig. 46, and almost 
immediately an agitated spiral* was formed, as 50, fig. 46, at the positive, 
extending nearly the whole length of the tube, but there were at the 
negative two or three saucer-shaped steady strata convex towards it. In the 
rotating mirror it was seen that there was a steady flow towards the 
negative. The characteristic hydrogen lines were very brilliant when the 
spectroscope was directed to the glow around the negative terminal, but 
quite a different spectrum was seen on a bright stratum, with mercurial lines 
in the orange. Shortly after this, the current being very great, the bent wire 
was heated to redness and fell down as in 56, fig. 46. 
44. — Pressure 1*2 m.m., 1579 M, 3600 rod cells, (C.) 0'019940 W. A 
beautiful formation of 72 saucer-shaped strata from the positive, one of 
which is seen as about to detach itself, the other strata were less convex 
towards the middle of the tube, and lip shaped near the negative, all 
being of a fine cobalt blue colour, 55, 56, fig. 46 ; on introducing 250,000 
* Gassiot (Phil. Trans., 1858, p. 4) describes a somewhat similar appearance, thus (in a Torricellian 
vacuum) : “As the mercury ascends in the tube the stratified discharge from the positive wire collapses, 
giving the appearance of a compressed spiral,” 
