some Experiments with Rontgen's Rays. 165 



nons regions divided by a fine oblique black line which is in 

 the plane of the antikathode (fig. 4). If the pump goes on 



Fig. 4. 



working, in two or three seconds, or while only a few cubic 

 centimetres of mercury pass through the pump, the pheno- 

 menon changes. The luminosity behind the antikathode dies 

 out, and that in front of the antikathode increases; so that 

 there is seen simply a bright anterior region ending at the 

 oblique plane of the antikathode, beyond which all is dark 

 (fig. 5). This oblique delimitation can also be seen in the 



yellow phosphorescence upon the walls of the bulb. This 

 sudden transition occurs after the resistance of the bulb has 

 passed its minimum. The brightest luminescence occurs 

 when the spark-length exceeds 40-50 millimetres. The lumi- 

 nosity does not fall off* much even at very small angles to the 

 plane of the antikathode, proving that the emission of ar- 

 rays does not follow Lambert's law of the cosine by any 

 means, Experiments on this point are still in progress, 



