486 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
which stratification is of the ordinary character, with the exception that, at the crossing 
of the two tubes, a wider stratum is produced. While the discharge was passing 
through only one of the tubes a faint illumination was also produced in the two 
branches of the other, but it was not stratified. 
The two component tubes were subsequently connected with two separate batteries, 
each of 3600 cells, A and B ; A with the poles P and 1ST to the vertical component, 
and B with the poles P' and 1ST to the horizontal one. The effect is represented in 
Plate 36, fig. 15. It will be seen from the configuration of the strata at the cross, in 
this case when the currents were equal 0'00833 ampere, that the discharge of A goes 
from P towards N only as far as the cross, then turns off to the left to 1ST, the 
negative of the other battery, B, while on the other hand the discharge of B from P' 
goes to the N of A battery. 
The case is different if an external resistance is introduced in one of the discharges, 
as for instance in Plate 36, fig. 16, where, by the insertion of a resistance of 500,000 
ohms in the B battery connected with the horizontal tube, the current was reduced to 
about one-tenth (0‘000 8 7 ampere) of that of battery A connected with the vertical tube, 
the discharge from A battery goes on direct from P to N and the discharge from B from 
P' to N'. The different sizes of the two sets of strata render this evident. There is a 
bending down, however, of the strata of the weaker discharge at the cross in conse¬ 
quence of the action of the stronger one. One cannot but be impressed from this and 
other experiments before and hereinafter described by the apparent plasticity of the 
aggregate assemblage of molecules which constitute a stratum, for it evidently yields 
to external influences which modify its form. For instance, in Plate 36, fig. 17, copied 
from a photograph taken on a dry plate in half a second, the strata at the cross, pro¬ 
duced by two equal batteries of 3600 cells, are so far modified in both tubes that 
the curvature of one stratum in each branch is made convex towards the positive 
instead of concave. The vacuum is of air at a pressure of 0’428 m.m., 563 M. The 
extremities of the vertical tube are both negative, and those of the horizontal tube 
positive, so that in each tube positive is opposed to positive and negative to negative. 
In Plate 36, fig. 18, representing a photograph of the tube when containing hydrogen 
at a pressure of 0'46 m.m., with a separate discharge of 3600 cells in each tube, a very 
close stratification is produced. The ends of the vertical tube are both negative, those 
of the horizontal positive, each set of strata pursues its undisturbed course and pro¬ 
duces a beautiful configuration at the cross where the last stratum in the two 
horizontal branches remains concave towards its own positive, but in the negative 
branch becomes convex towards the negative, yielding as it -were to the influence of 
pressure of the strata from the positive. 
In Plate 36, fig. 19, the two sets of strata follow their proper course leaving a 
dark interval at the cross between them. The tube contained air at a pressure of 
0'423 m.m., 563 M, the batteries used being both 3600 cells, the positive of A 
battery was connected to the top of the vertical tube, and its negative to the left 
