1908-9.] Negative Attempt to detect Fluorescence Absorption. 413 
suppose that a negative electron is moving in an ellipse inside a sphere 
of positive electricity of uniform density p. Its period is then 
e being the charge on the electron and m its mass. Let us suppose that 
the electron executes forced vibrations under the action of the incident 
light, the amplitude increasing until it flies out of the sphere. It will then 
move in an ellipse under the inverse square law, the period being 
3i rm r 3 
pe a? 
where r is the mean diameter of the path and a the radius of the sphere. 
The period is now longer. We shall suppose that in this state the electron 
loses kinetic energy by radiation and finally falls back into the sphere, 
and that the process is again repeated. We should have in addition to 
assume the existence of irregular impacts on the sphere due to collision 
with other spheres, otherwise the electron would remain on its surface. 
This model has the advantage of explaining why the fluorescent light 
has a longer wave-length. Unfortunately it does not give it a definite 
period. 
The research described in this article was carried out in the Physical 
Laboratory of the University of Glasgow. The spectrophotometer employed 
was the property of the Carnegie Trust for the Universities of Scotland. 
(Issued separately July 8 , 1909 .) 
