134 THE ROYAL SOCIETY OF CANADA 



From an examination of the diagram it will be seen that before 

 electrons are in a position to emit by their return to stable orbits 

 radiation corresponding to certain wave lengths, they must be lifted 

 out to definite orbits by the absorption of radiant energy or by colliding 

 electrons of proper velocity. The electron may now return to its 

 original orbit emitting radiation of wave length equivalent to the 

 energy absorbed. If the temporary orbit in which a displaced elec- 

 tron may be situated is more than one orbit removed from the stable 

 one, the return of the electron may possibly take place by intermediate 

 stages. Again, if the electron has been lifted from its stable position 

 to an outer orbit by the absorption of energy, it is then in a position 

 to absorb more energy, suitably quantized, so as to be lifted to a more 

 distant orbit. From this one it may be possible for it to return to 

 its original position by a variety of transitions. For example, where 

 an atom of mercury absorbs light of the wave length X= 1849.6 A.U. 

 the electron is lifted to the (2, P) orbit. If, when it is in the (2, P) 

 orbit, it absorbs energy of the wave length X== 10141 Â.U. it is still 

 further lifted to the (2.5, S) orbit. According to the diagram this 

 electron is now in a position to return to the stable orbit in at least 

 two ways. It may return along the same path emitting the wave 

 lengths X= 10141 Â.U. and X = 1849.6 Â.U. or it may pass from the 

 (2.5, S) orbit to the (2, p,) orbit emitting the wavelength X = 4078.05 

 A.U. and from the (2, p-i) orbit to the stable orbit (1.5, S) emitting 

 the wave length X = 2536.72 Â.U. 



On this basis it will be seen that when mercury atoms absorb 

 light of the wave length X = 2536.72 A.U. electrons are lifted to the 

 (2, pi) orbit. These atoms are then in a condition to absorb the light 

 of all wave lengths for which the orbit (2, p<i) is the initial orbit of 

 an absorption process, that is, they are able to absorb light of the 

 wave length X = 4358.66 k.\J.-[v={2, p2)-{1.5 s)]-or of the wave 

 length X = 4078.05Â.U.-[v=(2, p.^-{2.5, S)]. On the return to 

 the stable orbit (1.5, S) the electron may pass into one of the (2, p) 

 orbits giving rise to the emission of the wave lengths X = 5460.97 A.U. 



X = 4358.66 Â.U. or X = 4046.78 Â.U. On the other hand on the 

 absorption of the wave length X = 4078.05 A.U. the electron is lifted to 

 the (2.5, S) orbit. Now it may return to the (2, P) orbit giving rise 

 to the emission of X = 10141 Â.U.-U=(2, P)-(2.5 S)], etc. Fig. 3 

 is an alternative method of illustrating the same process. 



If the wave lengths corresponding to the return to the (1.5, S) 

 orbit from one of the (2, p) or the (2, P) orbits are not all known, it 

 may perhaps be explained by the fact that they have been too faint 

 to be recorded photographically. 



