1922] Proceedings of the Academy of Science 17 



these Ocoee slates are Post Carboniferous, and that some of the 

 larger granitic masses to the east of the Ocoee proper are probably 

 also of Post Carboniferous age. 



The Variation of the Photoelectric Current With Thickness of Metal. 



Otto Stuhlman, Jr. 



Silver and platinum deposited in the form of transparent and semi- 

 transparent wedges were examined for variation of the photoelectric 

 current as thickness of the metal was increased. The metal was 

 deposited on quartz by the evaporation method and examined when 

 monochromatic light fell on the metal side of the plate. 



The results are found to be consistent with the view that the prob- 

 ability of an electron going a given distance without losing its ability 

 to escape falls off exponentially with the distance, when this distance 

 is less than about 40 mm. Up to this thickness there is a parallelism 

 between optical absorption and photoelectric emission. For large 

 wave-lengths this parallelism is more pronounced than for short wave- 

 lengths. For greater wave-lengths optical absorption may increase 

 but photoelectric emission decreases terminating at the threshold 

 value of photoelectric sensitivity. 



The results seem to support the view that photoelectric emission 

 is probably not caused by the absorption of energy out of the inci- 

 dent light beam, the light only acting as the agent which sets the 

 electron free from its parent atom. 



Geology of the MuscU Shoals Area, Alahama. W. F. Prouty. 

 Appears in full in this issue. 



Chemistry in Its Eelation to the State Water Supplies. G. F. Catlett. 

 Appears in full in this issue. 



The following papers were presented but no abstracts have been 

 received : 



The Dipterous Galls of the Hickories. B. W. Wells. (Lantern). 

 Instincts in Social Life. (By title). C. C. Taylor. 

 The Effect on Tops of the Wilting of Succulent Vegetables. L. B. 



Rhodes. 



The Polymorphic Genus Clavaria. W. C. Coker. 



