THE X RAYS. 777 



were of the nature of electrical currents, they ought, being of the 

 same sign, to attract each other. This experiment seems to point 

 to an electrostatic nature of the cathode rays. The electrostatic 

 lines of force go out from a charged conductor at right angles to 

 the surface of the conductor. I have had constructed a Crookes 

 tube with two parallel terminals of aluminum. The fluorescence 

 in the walls of the vessel, when it was exhausted, showed that 

 the cathode rays went out from every element of the cathode at 

 right angles to it. By bending it into an arc of a circle the cath- 

 ode beams traveled over the surface of the vessel, forming zones 

 of light the centers of which were in the bent wire. Is it not pos- 

 sible that by the electrostatic action the few molecules of air left 

 in the high vacua are shot off with great velocity and bombard 

 the walls of the vessel, thus giving rise to the fluorescent light, 

 and also giving rise to an agitation of the molecules of matter 

 outside the vessel ? This may be called the molecular view of the 

 phenomenon. I confess it is difficult to see why the molecular 

 agitation is stopped by a thin sheet of glass and not by an inch of 

 wood. It is certain that a few molecules must be left in the 

 high vacua, for the cathode rays can not be formed in a perfect 

 vacuum. 



It is also true that it is useless to attempt to obtain photo- 

 graphs in any reasonable time from tubes which do not show a 

 strongly marked cathode beam, or from tubes which on revers- 

 ing the electric current through them do not show a marked dif- 

 ference between the light at the cathode and that at the anode. 

 In poorly exhausted tubes one can perceive a faint appearance 

 of a cathode beam, which is lost at a short distance from the 

 cathode, as if the molecules which are shot off meet with such a 

 crowd of more slowly moving ones that their energy is soon lost, 

 and the cathode beam is quickly diffused like a beam of sunlight 

 passing into milk and water. Thus the beam of cathode or X rays 

 emerging from the glass vessel into the air is soon no longer con- 

 ical in form. The sides of the cone of rays are no longer straight ; 

 they are curved, as if the generatrix of the cone were a curved 

 line instead of a straight line, and the beam is soon lost in a 

 turbid medium. One can imagine a stream of projectiles being 

 similarly dispersed in striving to pass into a region of sluggishly 

 moving shot. This molecular view of the phenomenon seems at 

 first sight to be a more tangible one than the longitudinal wave 

 theory. It is possible, too, that the impact of the molecules on the 

 aluminum window of Lenard, or on the glass sides of the vessel, 

 may serve to start ripples, so to speak, in the ether, which are 

 propagated with the velocity of light. 



The Rontgen phenomenon seems to be a manifestation of 

 cathode rays brought to light and endowed with great practical 



