380 Prof. E. Goldstein on 
This apparently so powerful effect of a magnet on the 
direction of the canal rays is primarily conditioned by the 
change in the direction of the Sprays which results from 
the approach of the magnet. Yet even this strong effect on 
the Sprays is not primarily due to the magnet, the primary 
effect being the magnetic deflexion and distortion of the 
common cathode rays which excite phosphorescence, and the 
approach of their extremities towards the cathode. If, for 
instance, the magnet deflects the rays towards the right hand, 
then a certain portion of the right-hand wall on which the 
condensed rays impinge becomes a secondary cathode, which 
attracts the rays of the first layer, and, by causing them to 
be attracted towards a region lying nearer the cathode than 
before, inclines them more towards the right. The con- 
sequence is that the right-hand boundary of the convergent 
canal-ray band becomes inclined even more obliquely upwards 
and towards the left. — Let it be expressly stated that the 
possibility, in addition, of a direct effect of the magnet on 
the Sprays is not denied. 
If a gold wire be arranged as cathode along the axis of a 
cylindrical tube, then, as is well known, a deposit of gold is 
produced on the wall around the cathode (in an atmosphere 
free of oxygen). On replacing the wire by a double square 
of material (aluminium) which does not disintegrate, with 
the planes of the squares normal to the axis of the tube, and 
on producing the cross-shaped system of canal-rays depicted 
in tig. 2, it is found that after a comparatively short time the 
thickness of the gold deposit is very materially reduced in 
the four places where the arms of the cross meet the tube, 
and ultimately the wall of the tube is in those regions denuded 
of gold. This property of canal rays may be exhibited in a still 
more striking and technically more convenient manner by in- 
troducing into a tube a double cathode of material subject to 
disintegration (silver, gold, nickel), in which case those places 
where the arms of the cross strike the tube remain entirely 
free from deposit. These regions are in general of a rhombic 
shape. When they have been mapped out, it is found that 
on rotating the cathodes about their axis through, say, 45°, 
the regions formerly free from deposit become covered, while 
.the already covered regions where the rays impinge against 
the tube become denuded. In general, the particles deposited 
are transferred from the places where the canal rays have the 
greatest density to places of lower density *. 
* [Note, Jan. 30th, 1908.]— Later on Prof. J. J. Thomson (Proc. 
Cambridge Phil. Soc. xiii. p. 212, 1905) has also observed that canal rays 
disintegrate metallic surfaces, and the same statement has been made by 
Mr. Kohlschiitter (Zeitsc/ir. f. Elcktroehemie, xii. p. 869, 1906). 
