ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 223 
Throughout our researches we . have not seen in a carbonic acid vacuum any 
umbrella-, saucer-, or tongue-shaped strata as shown in Plate 11, figs. 2, 6, and 7, 
respectively ; so far as our experience goes they are always of the disc-form shown in 
figs. 8, 9, 10, 11, 12, Plate 16, and fig. lh in Plate 17. 
On the other hand, hydrogen, phosphoretted hydrogen, and arsenetted hydrogen 
will give the umbrella-, saucer-, and tongue-like strata. 
Some tubes containing sulphurous acid give these forms of strata, while cyanogen 
gives the disc-shaped as in carbonic acid. 
Tubes prepared by Dr. Geissler containing a mixture of gases, such as phos- 
phoretted hydrogen and hydrogen, carbonic acid and bromine, nitrogen and bromine, 
as a rule give a most beautiful stratification and point to the desirability of a more 
extended study of the effect of mixture of gases on the electric discharge. 
In 1875 we made a communication to the Poyal Society, in connexion with our friend 
Mr. Spottiswoode, on Electrical Discharges in Vacuo,'" in which were described some 
phenomena bearing on the cause of stratification in vacuum tubes ; we have recently 
repeated the experiments obtaining the same phenomena, and we have, this 
time, recorded them by photography, as shown in Plate 18, fig. 6, a and b, fig. 7, 
a and b, and fig. 8, a and b. The diagram, fig. 66, exhibits the arrangement of the 
Fig. 66. 
V 2 
apparatus ; S Z, a battery of 1080 cells connected at one terminal, S, to the primary 
of an induction coil P P', thence to the straight wire of the vacuum tube V, the other, 
a ring in this case, being connected to the Z terminal of the battery ; the positive 
current consequently passed from S through P P', and through the tube V. The 
secondary wire S S' of the induction coil was connected to a tell-tale tube V 2 . Under 
* Proc. Roy. Soc., yol. xxiii. p. 356, 1875. 
