Poiver of Positive Rays to produce Phosphorescence. 615 



power of producing phosphorescence and of affecting a 

 photographic plate. 



The particles of the positive rajs being nearly of the same 

 nature as the a rays of the radioactive elements, an abrupt 

 stopping of the power of producing phosphorescence of the 

 canal rays was to be expected. The experiment was made 

 with the tube shown in fig. 1. 



Fijr. 1. 



To PUMP 



To E/)f?TH 



A small Rontgen tube can be moved by means of an 

 electromagnet in an exterior tube of 70 cm. length and 

 3'3 cm. diameter. The cathode and the anode of the interior 

 tube are connected with the electrodes of the other tube 

 by means of spiral springs of copper ; the cathode of the 

 inner tube contains a tube with a hole of 1*5 mm. in diameter, 

 so as to project canal rays into the outer tube ; the cathode 

 is earthed. The two tubes communicate with each other by 

 the tubular cathode, and thus the pressure is the same in both 

 tubes. At the end of the exterior tube there is a phosphor- 

 escent screen of willemite ; a diaphragm with a hole of 1 cm. 

 in diameter nearly touches the screen. One half of the hole 

 is covered with a plate of quartz. Through the small tube of 

 the cathode there passes some ordinary light caused by the 

 phosphorescence of the glass of the Rontgen tube and masking 

 the effect of the phosphorescence of the screen, due to the 

 positive rays. The quartz absorbs all the positive particles, 

 and the part of the screen behind the quartz becomes luminous 

 only by the ordinary light passing through the quartz. 



The vacuum was sufficiently advanced when a visible beam 

 of positive rays passed through the hole of the cathode, and 

 the glass wall of the Rontgen tube began to be luminous by 

 the impact of the cathode rays. The interior tube usually 

 lay at the positive pole of the outer tube, at the opposite end 

 to the willemite screen, which received in this position of the 

 Rontgen tube only a very small amount of ordinary light. 



On moving the interior tube towards the willemite screen, 

 it was found that at a certain point the phosphorescence due 



