220 Sir J. J. Thomson : Farther 



The fact that the smallest electrostatic deflexion of the 

 prolongation is just half that of the corresponding deflexion 

 of the primary, shows that the swiftest of the particles in 

 the prolongation has twice the kinetic energy of the swiftest 

 in the primary ; and hence when in the electric field in the 

 discharge-tube they have acquired twice the kinetic energy of 

 the normal particles : they must therefore have had twice the 

 normal charge when in the discharge-tube, but after they get 

 into the deflecting fields the value of e/m must be normal. We 

 Infer from this that when in these fields the charge is normal ; 

 for though we should get the right value of e/m if both the 

 charges and the masses were doubled, the double charge 

 Would for the same kinetic energy produce double the 

 electrostatic deflexion, and therefore lor a particle with twice 

 the normal kinetic energy would give the normal deflexion : 

 the actual electrostatic deflexion in the prolongation is, how- 

 ever, only half the normal deflexion. We conclude therefore 

 that the prolongation is due to particles which had a double 

 charge when in the discharge-tube, but which have lost one 

 of their charges after having passed through the cathode. 



The prolongations We are considering only occur with 

 certain types of lines* Speaking generally, they are confined 

 to lines due to atoms as distinct from those due to molecules; 

 and moreover, when we find these prolongations we generally 

 find on the same plate lines having a value of e/m twice that 

 of the prolongations and beginning in the normal place ; 

 these are due to the particles wdrich have retained their 

 double charge after passing through the cathode. 



On the line due to mercury we find prolongations corre- 

 sponding to particles which had three charges before passing- 

 through the cathode, and which have lost two of these charges 

 after doing so ; the heads of these prolongations are only one- 

 third the distance from the vertical of the normal heads. 

 We find also on the plate lines due to mercury atoms with 

 three charges which have retained these charges after passing- 

 through the cathode. The ability of the mercury atom 

 to acquire multiple charges may be the reason why the 

 parabola due to the mercury atom comes up much closer to 

 the vertical than the parabolas due to other atoms. This is 

 often very conspicuous : for example, the mercury line shown 

 in PL IX. fig. 13 is parabolic, even when quite close to the 

 origin. 



Measurements of this curve show that some of the mercury 

 atoms must have four or five times the kinetic energy possessed 

 by the atoms of the other gases. It is possible that the heavy 



