Magnetic Rays. 309 



column fills in the side tube. As the magnetic field increases 

 the second negative bright band gradually lengthens and 

 creeps into the large tube, until at the critical intensity the 

 whole tube is filled suddenly with a glow discharge. If 

 the magnetic field be still further increased, the discharge 

 attains a maximum length and definition, and then diminishes 

 in length. From B to E the light is similar in colour to the 

 cathode rays in air, and from E to F it is reddish or more 

 like a positive column. At E, the two parts of the column 

 are separated by a rather dark space. 



If the magnet S is held with its axis horizontal and with 

 its pole near the portion of the tube between B and E, the 

 rays bend in the arc of a horizontal curve. They bend 

 toward the pole of the magnet, if this pole is of opposite sign 

 to the nearer pole of the magnet R; and they bend directly 

 away from S if the poles are similar. On the other hand, an 

 electrical field produces no effect on these rays. That is, the 

 rays act as if they were composed of a moving stream of 

 electrically neutral particles which are at the same time 

 elementary magnets. Because of these actions, Professor 

 Righi has applied the term " magnetic rays " to this part of 

 the column. 



The rest of the column EF has its origin in these 

 magnetic rays and will be called the induced ray. If S is 

 held horizontally and with one pole near the induced ray, 

 the column bends vertically like the positive column in a 

 Geissler tube. The curvature of the ray is the same as 

 would be produced by a similar magnetic field acting on a 

 current of positively charged particles moving from E to F. 

 The action is seen more clearly if electrostatic discharges 

 are prevented by enclosing the tube in an earthed metallic 

 screen of: copper gauze. 



When the conditions are such that a very long induced 

 column is formed, a different effect is shown by the magnet 

 S. As it is moved along the tube a point is reached, indicated 

 by p in fig. 2, where the light splits into two helically 



Fig. 2. 



J- • -L 



curved bands. Then as the magnet is moved toward E or 

 toward F, the bending of the column is opposite in curva- 

 ture ; if it bends up on one side, it bends down on the other. 



