the Canal-Ray Group. 381 
To a smaller extent, the ordinary cathode rays also possess 
the property of disintegrating metal surfaces against which 
they impinge, as I have previously shown*. Grandquist has 
pointed out in this connexion that the minimum thickness of 
deposit occurs where there is a maximum of phosphorescence f. 
In comparative experiments carried out by myself, the action 
of the canal rays was markedly stronger. A separation of 
the two kinds of rays may be effected by means of the strong 
magnetic deflexion exerted on the ordinary rays which excite 
phosphorescence. 
Connected with this transport of metallic particles are the 
traces which are left in the canal rays on the cathode surfaces 
after continued use. Mere differences of colour and reflecting 
power may already be obtained in a very much shorter time, 
and, as mentioned above, depend on the formation of layers 
of oxide. 
The bands and narrow cones of the canal rays are — even 
in the case of cathodes completely filling the opening of the 
tube — surrounded by a duller, but very easily noticeable, 
nebulous light, which fills the entire space even in the case 
of cylindrical tubes of large cross-section, or spheres 10 cms. 
in diameter. In order to investigate this light more closely, 
it is convenient to make use of plate screens completely filling 
the opening of the tube and provided with only a single slit 
or hole. It is thus possible to establish the fact that this 
light contains two forms of radiation. One of these consists 
— as may be ascertained from the shadows cast by suitable 
objects — of regular, rectilinear, divergent rays, which proceed 
from the slit (or hole) in the form of a wide cone, enveloping 
the canal rays proper. The aperture of the cone exceeded 
120° in my experiments. If the S r rays which proceed from 
a slit viewed end-on be deflected to the right by a magnet, 
the nebulous rays in the left-hand portion of the tube become 
brighter. The luminescence of sodium &c. may be excited 
by these rays just as well as by the canal rays proper. At 
low gaseous pressures, these regular nebulous rays cast deep 
shadows, which appear quite dark. But with increasing 
pressure the space corresponding to the shadow becomes 
gradually filled with the second form of radiation, which 
consists of diffuse rays. These are produced in a much 
weaker form in hydrogen than in air (or nitrogen), in which 
they exhibit a golden-yellow colour. 
* E. Goldstein, TliatiqkeiUbericM cler Phys.-Tech. Reichsanstalt fur 
1894, p. 70 ; Zeitschr.f. Instrumetvbenk. xvi. p. 211 (1897). 
f G. Grandquist, Oefvers. Fovhandl. Svensk. Akad. 1897, p. -575. 
Phil. Mag. S. 6. Vol. 15. No. 87. March 1908. 2 D 
