the Canal-Ray Group. 383 
divergent in planes parallel to the cathodes — whose rays are 
also slightly divergent in a plane normal to the cathodes, in 
a manner similar to that of the star-rays themselves, as shown 
in fig. 5. The objective existence of the dull fan-shaped 
pencils of rays which fill up the gaps between the rosy arms 
of the star may also be shown by using double cathodes o£ 
material which undergoes disintegration. It is then observed 
that, in addition to the regions entirely free from deposit 
which correspond to the intersections of the bright arms with 
the walls of the tube, there also appears around the wall a 
moderately wide zone in which the deposit, though present, 
is markedly reduced in thickness, as may be seen by trans- 
mitted light. In accordance with this, it is also found that 
in planes which are normal both to the planes and to the 
sides of the double cathodes, there proceed from the spaces 
between the plates dull, rectilinear rays, in the form of very 
wide, divergent, very feeble, wide-angled fans of rays which 
accompany the moderately divergent and easily seen rays 
represented in fig. 5. These strongly divergent rays, whose 
planes of divergence are normal to the plane of symmetry of 
the double plate, are to be regarded as analogous to the 
rectilinear nebulous rays mentioned above. 
In the formation of the moderately divergent pencils shown 
in fig. 5 there may also take part — in the case of double 
cathodes — rays which, like the Sprays, appear to proceed 
from the inner surfaces of the plates, more especially from 
prominent lines and symmetrically situated points of the 
polygonal surfaces ; in the case of rectangles, e. </., from a 
portion of the bisecting line parallel to the longer sides. The 
rays traverse a short distance in a direction nearly normal to 
the plate, and are then deflected towards it through a large 
angle. According to the amount of this deflexion, which 
changes with the pressure, they enclose, together with the rays 
proceeding from the other plate, spaces of varying shape. 
Thus at low pressures and with a relatively small deflexion 
they converge with the corresponding rays of the other plate 
and form a convergent middle sheet in the outwardly divergent 
beam of fig. 5. A more detailed account of these very com- 
plicated relationships of the rays cannot, however, be given 
within the limits of a general sketch. 
Up to the present, it has been possible to identify (at least) 
the following members of the canal -ray group : — 1. The rays 
of the first layer. 2. The canal rays proper. 3. The K^-rays, 
which also occur at the front surfaces of continuous (not 
perforated) cathodes. 4. Regular nebulous rays, which 
envelop the canal rays proper. 5. Diffuse rays. 
The above list might be extended. 
2D2 
