1907.] on Rays of Positive Electricity. 583 



Since 



y B 

 X A 



y- _ B- m 

 X A e' 



We see that if the pencil is made up of rays having a constant 

 velocity, but having all values of ^ up to a maximum value, the spot 



of light will be spread out by the magnetic and electric fields into a 

 straight line extending a finite distance from the origin. While if it 

 is made up of two sets of rays, one having the velocity v-^ the other 

 the velocity Vo, the spot will be drawn out into two straight lines as 

 in Fig. 4. 



If — is constant and the velocities have all values up to a maxi- 

 m 

 mum, the spot of light will be spread out into a portion of a parabola, 

 as indicated in Fi^. 5. 



Fig. 4. Fig 5. 



We shall later on give examples of each of these cases. 



The discharge was produced by means of a large induction coil, 

 giving a spark of about 50 cm. in air, with a vibrating make and 

 break apparatus. Many tubes were used in the course of the investi- 

 gation : the dimensions of these varied shghtly. The distance of the 

 screen from the hole from which the rays emerged w^as about 9 cm., 

 the length of the parallel plates about 3 cm., and the distance between 

 them • 3 cm. 



^Properties of the Positive Rays when the Pressure is not 

 exceedingly loiv. _ 



The appearance of the phosphorescent patch after deflection in the 

 electric and magnetic fields depends greatly upon the pressure of the 

 gas. I will begin by considering the case when the pressure is com- 

 paratively high, say of the order of 5V ^^' ^^ ^^^^^ pressures, 

 though the walls of the tube in front of the cathode were covered 

 with bright phosphorescence and the dark space extended right 



