570 Prof. J. J. Thomson 



C)l 



at once an explanation, which I think is the true one, o£ the 

 continuous band into which the spot of phosphorescence is 

 drawn out by the electric and magnetic fields. The values 

 of e/m which are determined by this method are really the 

 mean values of e/m, while the particle is in the electric and 

 magnetic fields. If the particles are for a part of their course 

 through these fields without charge, they will not during this 

 part of their course be deflected, and. in consequence the 

 deflexions observed on the screen, and consequently the values 

 of e/m, will be smaller than if the particle had retained its 

 €harge during the whole of its career. Thus, suppose that 

 some of the particles constituting the positive rays, after 

 starting with a positive charge, get this charge neutralized by 

 attracting to them a negatively electrified corpuscle : the mass 

 of the corpuscle is so small in comparison with that of the 

 particle constituting the positive ray, that the addition of the 

 particle will not appreciably diminish the velocity of the posi- 

 tive particle. Some of these neutralized particles may get 

 positively ionized again by collision, while others may get a 

 negative charge by the adhesion to them of another corpuscle, 

 and this process might be repeated during the course of the 

 particle. Thus there would be among the rays some which 

 were for part of their course unelectrified, at other parts posi- 

 tively electrified, and at other parts negatively electrified. 

 Thus the mean value of e/m might have all values ranging 

 from a, its initial value, to —a! , where a' might be only a little 

 less than a. This is just what we observe, and when we 

 remember that the gas through which the rays are passing- 

 is ionized, and contains a large number of corpuscles, it is, 

 I think, what we should expect. 



At very low pressures, when there are very few ions in the 

 gas, this continuous band stretching from the origin is 

 replaced by discontinuous patches. 



Positive Rays in Hydrogen. 



In hydrogen, when the pressure is not too low r , the bright- 

 ness of the phosphorescent patch is greater than in air at the 

 same pressure ; the shape of the deflected phosphorescence is 

 markedly different from that in air. In air, the deflected 

 phosphorescence is usually a straight band, whereas in 

 hydrogen the boundary of the most deflected side is distinctly 

 eurved and is concave to the undeflected position. The ap- 

 pearance of the deflected phosphorescence is indicated in fig. 7. 



The result indicated in fig. 8, which was also obtained with 

 hydrogen, shows that we have here a mixture of two bands, 

 as indicated in fig. 4, the two bands being produced by carriers 

 having different maximum values of e/m. The greatest value 



