PROCEEDINGS 



or 



THE ROYAL IRISH ACADEMY 



PAPERS READ BEFORE THE ACADEMY 



I. 



PHOTO-ELECTEIC DISCHARGE FROM LEAVES. 



By PROFESSOR J. A. McCLELLAND, D.Sc, F.R.S., 



University College, Dublin, 



AND 



REV. E. FITZGERALD, M.Sc, Ph.D. 



[Read January 2. Published May 18, 1916.] 



The following paper contains an account of experiments dealing with the 

 photo-electric properties of leaves and flowers of various kinds, and of 

 substances extracted from the leaves. 



The source of ultra-violet light used was a spark between aluminium 

 terminals placed in the secondary of an induction coil, with suitable capacity 

 inserted in the circuit. We have not in any of the experiments described in 

 this paper used a source of definite wave-length, but in the further examina- 

 tion of some of the results we hope to do so. The original intention was to 

 see if photo-electric effects could be obtained from leaves, using sunlight as 

 the source ; but many interesting points arose in preliminary experiments 

 with the source described above, and the present paper is devoted to them. 

 The leaves or extracts under examination were placed on an insulated support 

 in a metal vessel, in the lid of which was a quartz window, with metal gauze 

 underneath, through which the light passed. 'J'he tray containing the leaves 

 or solution was joined to an electrometer, and the metal vessel, the lid of 

 which was parallel to the exposed photo-electric surface, was connected to 

 storage cells, and kept at a high positive potential, usually 240 volts. Care 

 was taken that the light after passing through the quartz and gauze fell only 

 on the surface under examination, the leaves or solution covering the surface 



R.I. A. PEOC, VOL. XX.YUI., SECT. A. [1] 



