CH. x.] RADIATION 109 



and presumably small hydrogen atoms ; and it is 

 owing to the comparatively easy migration of the 

 light or small hydrogen atom that acids are in 

 general such good conductors. 



The Hall magnetic bend, like Faraday's magnetic 

 rotation, is a differential effect, and would be zero 

 if positive and negative were equally acted upon. In 

 gases it is differential too, but there the negative 

 charges are liable to be so free as compared with 

 the positive, and to be so conspicuous, that the Hall 

 effect in gases, especially in rarefied gases, is very 

 great in comparison with the small residual effects 

 found in liquids and solids. Consequently the 

 effect of a magnet in curving the path of cathode 

 rays in a Crookes tube is readily demonstrated. 



Radiation. 



But it is not only the progressive motion or loco- 

 motion of the electric atomic appendages that we 

 have to consider ; we must assume also that they 

 are susceptible of motion in the atom itself, either 

 vibrating like the bead of a kaleidophone, or re- 

 volving in a minute orbit like an atomic satellite. 

 Indeed it is to the concerted vibrations or revolu- 

 tions of the system of electrons, in, or on, or round, 

 an atom, that its radiating power is due. Matter 

 alone has no perceptible connection with the ether, 

 a fact which is proved in my paper in the Philo- 

 sophical Transactions for 1893 and 1897;* it is 

 electric charge which gives it any connection, and 

 even then it has no viscous connection there is no 

 connection that depends upon odd powers of velocity, 

 so as to be of the nature of friction, t it is purely 



* Lodge, Phil. Trans., vol. 184, pp. 727-804, and vol. 189, pp. 149-166. 

 t See especially Phil. Trans., vol. 189, p. 164. 



