606 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
different cause and that it is a result of certain phenomena which are discussed in 
Section XXIII. 
Next take a narrow strip of tinfoil about 2 inches in length and place it longi¬ 
tudinally along the tube. If it be connected to earth we shall find that the relief- 
phosphorescence produced is in the shape of a broad patch occupying, say, half the 
circumference of the tube (Plate 27, fig. 14). It is, however, far from being uniform in 
brightness. Exactly opposite to the strip of tinfoil there is an ill-defined longitudinal 
band that is brighter than the surrounding parts, and which evidently corresponds to 
the bright central patch that was observed in the former experiment. From this band 
there branch out narrow bright streamers all perpendicular to the general direction of 
the band and giving to the glass a striped or striated appearance. These extend 
throughout the whole of the phosphorescent area, the spaces between them being less 
bright, though doubtless they are also phosphorescent, but to a less degree than the 
striations. 
It will be at once seen that no mere superposition of the phosphorescence of the 
elemental areas composing the strip could produce such a distribution of luminosity 
in the phosphorescence due to the whole strip. The streams that proceed from the 
different elements of the strip must therefore interfere with each other. And it is 
easy to see how this interference leads to the configuration described above. The 
strong repulsion between an element of the surface of the glass beneath the tinfoil and 
the particles of gas in contact with it can no longer drive them off at all azimuths, for 
in the direction of the length of the strip there are equally active elements exercising 
an equally strong repulsion upon these particles. The only directions in which the 
streams can spread out are therefore those which are comprised in a plane normal to 
the direction of the strip through the element under consideration. Any accidental 
cause creating a difference in the intensity of the local action at any point of the strip 
(as, for instance, a slightly better contact with the glass) will cause the streams from 
one element to be rather brighter than those from another, and hence the phospho¬ 
rescent image of the tinfoil will appear to be striped or striated in the manner above 
described.* 
If the strip of tinfoil be placed at right angles to the direction of the axis of the 
tube and partially surrounding it, the same striated appearance will be visible in the 
relief phosphorescence, but the stripes or striations will now stretch along the tube in 
* It is impossible to see this effect without being reminded of the appearances produced by the 
volatilisation by the electric spark of a fine metallic wire placed upon a sheet of white paper or cardboard. 
From the general line of the wire there branch out in a direction normal to its length fine lines or 
striations precisely similar in shape and arrangement to those that appear in the phosphorescent image of 
the strip of tinfoil, only on a smaller scale. The cause of this striated structure is probably the same. 
The violent disruptive action that dissipates the metal in the wire is forced to drive it off in normal planes 
because the particles would be turned back into the plane by the action at the neighbouring elements of 
the Avire were they to commence to move in an oblique direction. 
