310 Mr Campbell, Discontinuities in Light Emission. 



Discontinuities in Light Emission. By Norman Campbell, 

 M.A., Trinity College. 



[Bead 8 November 1909.] 



SUMMAEY. 



1. Introduction. 



2. The ideas underlying the experiments. 



3. 4. The theory of the method of experiment. 

 5. General nature of the experiments. 



6 — 10. Mathematical theory of the interpretation of the observations. 

 11 — 15. The apparatus : 



11. The source of light. 



12. The photo-electric cells. 



13. The measuring instruments. 



14. The high resistance. 



15. Measurement of the instrumental constants. 



16. Numerical calculations showing the possibility of the experiment. 



17. Combination of the observations. 



18 — 20. The experimental difficulties which have prevented the at- 

 tainment of results. 



§ 1. The following pages are the account of an experiment 

 which failed. The occasional publication of a description of such 

 failures may be justified by two reasons, both of which appear to 

 me sufficient in the present case. In the first place, the theory of 

 the experiment may be of interest : and, according to the view 

 which is taken of the causes of failure, others better equipped for 

 the task may be induced to repeat the attempt, or others, to whom 

 the same idea may occur, may be saved from wasting their time. 

 In the second place, the methods of experiment, if they are novel, 

 though unsuccessful in their immediate object, may have other 

 applications. 



§ 2. The ideas on which the experiment was based are not 

 easy to describe in a brief title : a little explanation is needed. 



According to all modern theories of radiation, the emission of 

 light is discontinuous in time. Whatever may be the nature of 

 the radiators from which the light proceeds, there is little doubt 

 that their vibration is not continuous. They are set into vibration 

 by some external disturbance, such as the impact of electrons, and 

 continue vibrating until the energy so acquired is dissipated by 

 the damping due to radiation : they are then quiescent until the 

 occurrence of a fresh disturbance. 



But there are at least two theories of radiation which suggest 

 that light emission is discontinuous in space as well as in time. 



