Rays of Positive Electricity. 237 



Another gas in which the radiation is interesting is 

 mercury vapour. We get radiation corresponding to elec- 

 trical atomic weight 200, i. e. to the atom of mercury in both 

 the primary and secondary radiation. In the secondary 

 radiation we have, in addition, two other kinds, one with an 

 electrical atomic weight of 100, which is probably an atom 

 of mercury with a double charge. The liability of the atom 

 of mercury to take a double charge will explain a peculiar 

 appearance which the line corresponding to the mercury 

 atom in the primary radiation often shows. This appearance 

 is represented in fig. 17. In addition to the bright comma a, 

 whose head is in the same vertical line as the heads of the 

 other bright primaries, there is, on the same parabola as a, 

 another bright spot, /3, whose horizontal deflexion is only half 

 that of a. Since ft and a are on the same parabola, the 

 value of elm is the same for the particles in ft as for those 

 in a, and since the horizontal deflexion of ft is only half that 

 of a, the kinetic energy of the particles in ft is twice that of 

 the particles in a. This would be just what we should find 

 if the particles in ft had had a double charge when they were 

 in the discharge-tube in front of the cathode and exposed to 

 the action of the electric field in the dark space, and lost one 

 of their charges after passing through the cathode and before 

 reaching the electric and magnetic fields. 



On some plates there are two bright patches on the parabola 

 corresponding to the hydrogen atom, but in this case the 

 horizontal deflexion of the abnormal spot is twice that of the 

 normal one. The simplest explanation of this spot is that it 

 is due, not to an atom of hydrogen with one charge, but to a 

 molecule of hydrogen with two charges, and that one of these 

 charges has been acquired after the molecule has passed 

 through the cathode. The doubling of the charge, if it arose 

 in this way, would not affect the kinetic energy, but would 

 double the deflexion produced by the electrostatic field, and 

 would put the spot on the curve for which e/m has the value 

 appropriate to the hydrogen atom with one charge. Fig. 17 A 

 shows a spot of this kind. 



The other type of secondary radiation in mercury vapour 

 is one with an electrical atomic weight of 8)0 ; this would 

 correspond to four atoms of mercury with one electric charge 

 between them. The existence of particles of this kind in the 

 secondary radiation, and of ;5 and 6 with oxygen, and H 3 

 with hydrogen, is experimental evidence for the existence of 

 aggregates formed round a charged ion. In one theory of 

 the electrical discharge through gases the existence of such 

 aggregates is assumed in order to explain why the velocity 



