488 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
Discharge in large tubes. 
In Part III., pp. 197-201, we described some experiments with a large tube 
37 inches (94 centims.) long, and 5y§ inches (14'8 centirns.) in diameter. We have 
again taken up the study of the discharge in large tubes 3 feet 2 inches (96‘5 centims.) 
long, and 6 inches (15'24 centims.) in diameter; the resulting phenomena are shown in 
Plate 35, figs. 11, 12, 13, and 14. In these, which are partly copied from photographs 
and partly from drawings made at the time in consequence of a to-and-fro movement 
of the strata preventing well-defined photographs from being obtained :— 
Plate 35, fig. 11, exhibits a discharge of 8700 cells with a current of 0'049 ampere 
in carbonic anhydride at a pressure of about O'5 m.m., 658 M. The strata near the 
terminals are not large enough to fill the whole bore of the tube, but they spread and 
become larger as they recede, and form a sort of conical expansion up to the wall of the 
tube. A rapid flow was observed from the negative with a still increased velocity, at 
intervals, producing a gap in the flowing strata of three times the interval between 
them. The three strata near the negative retained their position but rotated rapidly 
on their axes, and when looked at obliquely appeared dark in the centre and reminded 
one of a smoke vortex ring. 
Plate 35, fig. 12, represents the appearance in a hydrogen vacuum of about 0'5 m.m., 
658 M, with the same number of cells, 8700, producing a current of 0'047 ampere. 
After a short time the stratification receded towards the positive, leaving a long 
interval devoid of any towards the negative. 
Plate 35, fig. 13, represents the appearance of a vacuum of nitrogen and bromine 
with the same number of cells, 8700, giving a current of 0'047 ampere. After the 
discharge had continued for a few seconds the strata, as in the case of hydrogen, 
receded towards the positive end of the tube as shown in Plate 35, fig. 14. 
In all the foregoing cases a very beautiful and distinct stratification was produced, 
in the first instance, filling the tube just as in those of smaller bore, but near the 
terminals the strata became gradually smaller in a conical form, the gas itself for a 
certain distance acting as an enclosing tube. 
O O 
The dark negative space. 
In the dark space near the negative end of a vacuum tube the electric discharge is 
undoubtedly always passing, though not evident to the eye; but its passage is rendered 
apparent by the great heat at times developed within it, as we have already stated in 
Part II.* It occurred to us to endeavour to obtain a record of its passage by means of 
photography, and the result shows that it is actinically dark only by comparison. Tube 
No. 100, containing a residue of carbonic anhydride, gave, with 2400 cells and an 
* PHI. Trans, for 1878, Yol. 169, Part I., p. 182, Exp. 47 (separate copy, p. 98). 
