Multiply- charged Atoms. 671 



visible; but as the intensity of this parabola is very great it 

 might be thought that they escaped detection owing to the 

 breadth of the parabola. Let us therefore consider one of 

 the finer parabolas, say, that due to the atom with four charges, 

 to which this objection does not apply. 



This parabola might arise from atoms which had lost 

 8 charges on ionization and regained 4, from those which 

 had lost 7 and regained 3, and so on, the last being atoms 

 which had lost 4 and not regained any. Then if d has the 

 same meaning as before, the horizontal distances from the 

 vertical axis of the heads of the parabola would be 4x8c//8, 

 4 x Sd/7, 4 x Sd/6, 4 x 8d/5, 4 x 8d/±; there would, therefore, 

 he abrupt increases in intensity at 32<i/7, 32rf/6, 32^/5, 32c//4. 

 The photographs show, however, that the intensity is perfectly 

 continuous, and not one of these abrupt increases is to be 

 seen. We conclude, therefore, that there are no atoms 

 which begin with 7, 6, 5, 4, 3, 2 charges, and that in this 

 case there are two and only two types of ionization, in the one 

 type an atom loses a single corpuscle, in the other it loses 8. 



This result suggests that ionization takes place in the 

 discharge-tube in two ways. In the first method the ionizing 

 agents are the rapidly moving corpuscles which constitute the 

 cathode rays, these very small particles penetrate into the 

 atom and come into collision with the corpuscles inside it 

 individually, the collision in favourable cases causing the 

 corpuscle struck to escape from the atom; this type of ioni- 

 zation results in the atom losing a single charge. Jn the 

 other type of ionization we suppose that the mercury ate m 

 is struck by a rapidly moving atom and not by a corpuscle ; 

 after the collision the mercury atom starts off with a very 

 considerable velocity, which at first is not shared by the 

 corpuscles inside it. The tendency of the corpuscles to leave 

 the atom depends only upon the relative velocity of the atom 

 and the corpuscles inside it, so that the ionizing effect pro- 

 duced by the collision is the same as if the atom were at 

 rest, and all the corpuscles were moving with the velocity 

 acquired by the atom in the collision. Thus if there were 

 eight corpuscles in the mercury atom connected with about 

 the same firmness to the atom, the result of the atom 

 acquiring a high velocity in a collision might be the detach- 

 ment of the set of eight leaving the atom with a charge of 

 8 units of positive electricity. We see in this way how the 

 cathode particles might produce one type of ionization re- 

 sulting in singly charged atoms, while the atoms forming 

 the positive rays might produce another type of ionization 

 resulting in multiply-charged atoms. 



