MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
200 
tube varied from 130,000 to 160,000 ohms. This tube at first gave a 
beautiful stratification, but after several experiments, it merely showed a 
tendency to stratification towards the period of cessation of the current. 
At nearly the full potential one luminosity formed at the positive, a consider- 
able dark interval existing between it and another luminosity which formed 
in the centre of the tube, and there was a great interval between this and 
the glow at the negative. As the tension fell, the negative glow became 
globular, then elongated, and lastly reached the central luminosity ; suddenly 
the central luminosity disappeared, and left a dark interval in its place. This 
last phase is shown in fig. 60.* 
Eig. 60. 
TUBE 58. C02 
N P 
Tube 66, length between the terminals 28 inches, diameter 2 inches. 
Hydrogen. 
198. — The arrangement the same as for 197. With the full potential a splendid 
phenomenon of 18 steady strata was produced; as the potential fell more 
strata gradually crowded in from the positive until they reached 43 in 
number, after which they became confused. With 6,150,000 ohms resistance 
in circuit there was a rapid flow in which alternating greenish and reddish 
cross markings were seen ; the rotating mirror resolved these into strata 
alternately pink and greenish. The resistance of the tube was found to be 
* Gassiot (Proc. Roy. Soc., vol. xii., 1862-3, p. 336) describes a similar phase: “Depressing the wire 
very gradually (lessening the resistance) the positive became sharply defined, the negative retaining much 
of its irregular termination, but each separated by a dark interval of about one inch in length.” 
Mr. Spottiswoode informs us that at an early stage of his experiments he noticed the formation of 
large cylindrical blocks of light or luminosities, terminated by flat ends, and separated by dark intervals 
often as long as themselves. These were most frequently found in tubes from 2 to 3 inches in diameter, 
containing coal-gas residua, at 0'5 to 0‘75 m.m. pressure ; they were from 2 to 3 or even 4 inches in 
length, and sometimes shot out from the positive terminal, then travelled along the tube, and finally 
disappeared in the dark space towards the negative terminal. They could be produced either .by the 
Holtz machine with a very small air-spark, or with a coil furnished with one of the rapid contact 
breakers described in a paper (Roy. Soc. Proc. xxiii., 1875, pp. 455-462) referred to above. When 
observed with a revolving mirror these blocks usually showed striae in a state of flow. He is of 
opinion that, at all events when produced under the circumstances here described, these blocks are 
essentially stratified, and that they are sections of flow, even when the velocity is too great to allow the 
separate striae to be detected in the mirror. 
