178 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
tube. On approaching the finger it was repelled to the opposite side of the 
tube, and sometimes split into two portions, one on each side of the finger. * 
30. — At the 19ijr cistern-full 3600 would not pass, 4800 sufficed when the point 
was negative ; 7 broad strata crossed with lines of narrower strata not more 
than 0‘02 inch wide and distant. A zone of intensely blue light, 0'25 
inch broad, lined the inside of the tube around the point when negative. 
With 8040 cells the discharge was rustling when the point was positive, 
and if the primary of Apps’s induction coil 819 was connected in circuit, a 
tell-tale tube being connected to the secondary, the tell-tale became 
illuminated, indicating an intermittent current. 
31. — At the 22nd cistern-full, 4800 cells, no material change, except that between 
the blue zone and the end, the tube was filled with a pink glow, and that 
after a time even 8040 cells would not pass except when the point was 
negative ; but the next day 2400 cells passed in either direction even with 
an external resistance of 4,900,000 ohms, gas having probably been given off 
from the glass walls. 
32. — At the 29th cistern-full 8040 cells passed only when the point was negative, 
a milky light filling the whole tube ; heat was generated at the negative, 
very great in proportion to the light. 
33. — After 39 charges of the cistern had been sent through the Sprengel pump 
(since the vacuum had attained 0'2 m.m.) the current of 8040 cells would 
only pass after the contact with the battery had been maintained for some 
time and both ends of the tube alternately breathed upon ; in fact, the 
current had to be coaxed through it.t There were 9 barrel-shaped strata 
produced as shown in 38, a and b, fig. 45 ; the illumination was very feeble, 
and no lines could be made out with the spectroscope either in the strata or 
the luminous glow around the negative terminal, in this case the straight 
wire. Examined with the hand spectroscope the spectrum appeared indeed 
to be nearly continuous. In the course of our experiments we have often 
observed great changes in the spectrum of hydrogen as the exhaustion 
became greater, the C line, for example, is the first to get faint and then to 
disappear. J 
34. — The tube had now a small charge of hydrogen let into it, which raised the 
pressure to 0‘5 m.m., 658 M. 2400 rod cells with 500,000 ohms resistance 
in circuit, (C.) 0 '0047 18 W, produced 54 beautiful steady strata, some of 
which threaded themselves on the straight wire when it was made negative, 
exactly as in the case of Geissler’s tube 123 before, alluded to; b, 39, 
* The phenomenon was re-observed at a pressure of 0 '038 m.m., 50 M, 0. 0‘00631 W. 
t The limit of 8040 was subsequently attained at a pressure of 0’010 m.m., 21 M. 
J The variation in the spectrum of the same gas under different circumstances has engaged the atten- 
tion of several physicists — notably of Hittorf and Plucker (Phil. Trans, civ., 1865, pp. 1-30). 
