ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERV. 183 
55. — Pressure 4 '4 m.m., 5789 M, 8040 cells. 12 luminosities as depicted in 
fig. 6, Plate 15, which is copied from a photograph* obtained in 4 seconds. 
56. — Pressure 4'0 m.m., 5263 M, 8040 cells. 15 luminosities as shown in fig. 7, 
Plate 15, taken from a photograph in 4 seconds. 
57. — Pressure 3'6 m.m., 4737 M, 8040 cells, 30,000 ohms resistance. 15 lumi- 
nosities almost touching, like fig. 7, Plate 15. 
58. — Pressure 3 m.m., 3947 M, 4800 cells, C. 0'0362 W, the resistance of the 
tube being 88,600 ohms. There were 24 steady blue strata and a space of 
about 6 inches confused towards the positive ; with 200,000 resistance in 
the circuit the strata became pink, the current being 0'01469 W. 
59. — Pressure 1 m.m., 1316 M, 3600 cells, C. 0'03896 W, the resistance of the 
tube being 59,170 ohms. The tube was filled to within 1 inch of the 
negative with strata as in 85, fig. 46 ; all these were blue, but they turned 
pink and tongue-shaped when 200,000 ohms resistance was introduced, 
which reduced the observed current to 0 '007 8 2 W. The C and F lines 
visible in the luminosities. When 7,590,000 ohms resistance was intro- 
duced, a very close and somewhat agitated pink stratification was produced, 
like the left hand of 85, fig. 46. 
60. — Some gas let in, pressure 3 m.m., 3947 M, 3600 cells gave a current of 
0 '04901 W ; the resistance of the tube was ascertained by substituting 
47,000 ohms wire resistance, which produced the same deflection. The 
strata were blue, like those of 55 and 56, fig. 46. For about 10 inches 
from the negative they took up an axial backwards and forwards steady 
rotation of about a quarter turn. With 174,000 ohms resistance, making 
with the battery and tube a total of 261,000, the current measured was 
0 '008 79 W. The strata turned pink and assumed the tongue-form 57, 
fig. 46; with 783,000 ohms in circuit very close strata like the left hand 
of 85, fig. 46. In the rotating mirror a flow towards the 'positive was 
observed until a break occurred in the stratification; the flow was then 
irregular and backwards and forwards. 
61. — Pressure 1 '7 m.m., 2237 M. The current of 2400 cells passed : with 3600 cells 
the current was 0 '03 85 8 W, producing perfectly steady strata of which a 
photograph was obtained in four seconds ; a facsimile of it is given, fig. 8, 
Plate 15. The strata were blue, but on introducing 500,000 resistance the 
current was reduced to 0 '00 175 W, and the strata turned pink and assumed 
the form fig. 9, Plate 15, which is a facsimile of a photograph obtained in 
19 seconds. 
62. — Pressure 0'8 m.m., 3600 cells (C.) 0 19940 vv- -A- spiral series of tongues 
depicted in fig. 10, Plate 15, from a photograph which, however, could 
* Varley, C. F. (Proc. Roy. Soc., xix., 1871, pp. 288-239) succeeded in photographing by an exposure 
of thirty minutes an arch discharge in a vacuum tube, so faint that in a perfectly dark room he was 
“sometimes unaware whether the current was passing or not.” 
