ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
191 
occupying the centre of the tube. This column is usually striated, and 
ends in a stria with rounded head. 
(2.) On the side of the tinfoil towards the negative end of the tube a conical column of 
luminosity is seen to start from the inside of the tube immediately beneath 
the tinfoil, and to stretch towards the negative terminal. This cone, in fact, 
forms the base of the new positive column. 
(3.) On examination, this luminous cone is found to be hollow, the interior having 
an ill-defined and hazy surface in strong contrast with the somewhat sharp 
and regular outline of the exterior (Plate 16, fig. 10). 
Let us consider what is the explanation of these appearances. We know that 
strong pulsations of positive electricity pass to the positive terminal of the tube and 
the tinfoil, keeping time with the passage of the air-sparks. These pulsations, when 
they arrive at the terminal, are of sufficient intensity to cause a discharge to pass 
through the tube, and the pulsations that reach the tinfoil must be of exactly the 
same strength as those that go to the terminal. Such pulsations must drive off 
positive electricity in corresponding pulsations from the interior parts of the tube 
contiguous to the tinfoil. These latter pulsations are similar to the discharges that 
take place from the positive terminal, and they seek relief in the same manner, viz.: 
by rushing towards the negative terminal of the tube. In this process they form the 
hollow luminous cone mentioned above. These discharges of positive electricity from 
the inner surface of the tube leave behind them an excess of negative which would 
be held prisoned by the positive charge in the tinfoil if that were permanent; but just 
as the latter was generated by the momentary charging-up due to the passage of the 
air-spark, so it is released by the relief given to such cliarging-up by the discharge 
through the tube. On such discharge taking place, the negative on the interior of 
the tube is set free, and in its turn satisfies the positive electricity of the discharge that 
meets it in its passage from the positive terminal. Thus we naturally get the termina¬ 
tion of one positive column on the side of the tinfoil nearest to the positive terminal, 
and a complete discontinuity between it and the second, which starts in a hollow cone 
from the edge of the tinfoil nearest to the negative terminal. 
To show more clearly that this is the true interpretation of the phenomena, and 
that the effect of the arrangement is thus to substitute for the original discharge two 
independent discharges occupying different parts of the tube, take two or three such 
rings separated from each other by spaces somewhat less than the diameter of the 
tube and connect them as before with the positive terminal. Each of these will be 
found to be the base of a hollow cone similar to that above described ; and each such 
cone will form the base of a luminous column having all the features of a positive 
column, and terminating sharply behind the next tinfoil-ring or at the borders of the 
usual negative dark space near to the negative terminal of the tube. These sectional 
positive columns will be small in diameter and bright, and will or will not be striated 
according as their length is sufficient to permit of strife or not. If they are not 
