594 Professor Sir J. J. Thomson [Jan. 17, 



normal distance ; this proves that the argon atom can have as many 

 as three charges of electricity. If now you examine the krypton line 

 you will find that it comes nearer to the vertical line than even the 

 argon ; its least distance is one-fourth of the normal distance, showing 

 that the krypton atom may have as many as four charges. The 

 mercury line comes so close to the vertical line that it is only on large 

 photographs that it can be seen that there is in reality an interval ; 

 this interval is only one-eighth of the normal interval, showing that 

 mercury may acquire eight positive charges, i.e. that it may lose eight 

 corpuscles. The mercury atom when it is on this line must have 

 only the normal charge, i.e. it must have regained all but one of the 

 corpuscles it previously lost ; if it had retained two positive charges 

 it would have been on the line corresponding to the atomic weight 

 200/2 or 100 ; if it had retained 3, or 4, 5, 6, 7, 8, on the lines 

 corresponding to the atomic weights, 200/3, 200/4, 200/5, 200/6, 

 200/7, 200/8 respectively. All these except the last have been 

 detected on the plate. The lines corresponding to the multiple 

 charges on krypton, argon, and neon have also been detected. It 

 appears, then, that in a vacuum tube a mercury atom, for example, 

 may be ionized in two ways ; in the one way the atom loses one 

 corpuscle, in the other it loses eight. I would suggest that these two 

 types of ionization may result from the two different types of collision 

 which the atom must experience. The first type is collision with a 

 corpuscle ; since the corpuscle is an exceedingly small body moving 

 with a very great velocity, it can pass freely through the atom, 

 and the collision it makes with the atom is really a collision with 

 a corpuscle inside the atom ; this may result in the corpuscle it 

 strikes acquiring such a great velocity that it is able to escape from 

 the atom ; this type of collision will result in the detachment of a 

 single corpuscle. ^ The second type of collision is when the atom 

 collides with another atom and not with another corpuscle ; the result 

 of this collision may be that the atom suffers a sudden change in 

 its velocity. This change is not at first shared by the corpuscles, 

 so that these just after the collision may have a very considerable 

 velocity relative to the atom. If there are several corpuscles which 

 are comparatively loosely attached to the atom, these may all be 

 detached from it and leave it with a positive charge corresponding 

 to the number shaken out. It is this type of collision which we regard 

 as giving the multiply-charged ions, and we see that the magnitude 

 of the charge is a measure of the number of corpuscles in an atom 

 which are readily detachable from it. We have seen that the greater 

 the atomic weight the greater the charge it can acquire, the maximum 

 charge being roughly proportioned to the square root of the atomic 

 weight, hence the'heavy elements have a larger number of detachable 

 corpuscles than the lighter ones. 



Another application of the method I should like to bring before 



