2U Sir J. J. Thomson on the 



by Ladenburg on the energy possessed by the corpuscles 

 which are emitted by bodies when exposed to ultra-violet 

 light. Ladenburg found that the maximum energy of these 

 corpuscles was independent of the intensity of the light, 

 that it varied but little with the nature of the body from 

 which they were emitted, and was proportional to n the fre- 

 quency of the light, being of the order Wnj'lir where h' is 

 Planck's constant. These results admit of very straightforward 

 interpretation on the unitary view of the structure of Jight, 

 each corpuscle being regarded as taking up one unit of 

 energy from the light which caused its ejection. There seems 

 to me, however, to be grave objections to the assumption 

 that units of light are incapable of alteration ; for example, 

 why should a unit of light when passing over a corpuscle be 

 obliged to communicate to it either the whole of its energy 

 or none at all ? 



If we suppose that doublets exist in the atom, then 

 experiments such as Ladenburg's admit of a different inter- 

 pretation from that just given. If AB is a doublet with the 

 positive end at B, and P a corpuscle, then it is possible to 

 have a state of steady motion when P describes a circle 

 round AB as axis, the plane of the orbit being at right 

 angles to AB and the centre of the orbit on the prolongation 

 of AB. 



The equations of motion of a particle moving under the 

 influence of the doublet are easily found. Let ?=OP the 

 distance of the corpuscle from the centre of the doublet, 

 6 the angle which OP makes with AB the axis o£ the 

 doublet, and <f> the angle which the plane POB makes with a 

 fixed plane. Then m being the mass and e the charge on a 

 corpuscle, M the moment of the doublet, we have 



/ d / 9^n 2 • a alA M^sin 



\ 7/ v'v)~ r " sln cos 04* )= r~ 



?»y (V 2 sin- 00) = 0. 

 tic 



In the state of steady motion both r and 6 are constant 

 and v the velocity of the particle =7* sin 6^ hence we have 



~"~~ ir ~\ (3) 



, „ M*sin0 ( 

 cot u mv = — — 7, — ) 



