TRANSACTIONS OF SECTION A. 539 



no true fatigue. Recent experiments by Millikan and Winchester show no 

 fatieue with clean unpolished metal surfaces in a very high vacuum lo explain 

 the "fatigue found by other investigators we must take into account the mode ot 

 preparation of the surface (Ladenburg's plates were polished with emery and 

 oil), the difficulty of removing air films from the surface, and the possibility ot 

 changes in the gas pressure. 



Various theories have been advanced as to the nature of the change accom- 

 panying photoelectric fatigue : — 



(1) A chemical change, such as oxidation of the surface. 



(2) A physical change of the metal itself, as, for example, a roughening 



of the surface. . . tl . 



(3) An electrical change in the formation of an electrical double layer 



(Lenard). , 



(4) A disintegration of the metal, due to the expulsion of electrons by light 



(Ramsay and Spencer). ,,-,.., . , 



(5) A change in the surface film of gas or in the gas occluded in the metal 



(Hallwachs). . 



Hallwachs has shown from the photoelectric behaviour of copper and its 

 oxides that oxidation cannot be the cause of fatigue, and the fact that fatigue 

 is less in a small vessel may be interpreted by attributing it to some substance 

 (e.g., ozone, water vapour) present in small quantities in the surrounding 

 atmosphere. The results recorded lead to the view that the main cause of 

 fatigue is to be found in the condition of the gaseous layer at the surface of 

 the plate. 



Bibliography of Photoelectric Fatigue. 



[Ordered by the General Committee to be printed in extenso.] 



1887. 



H. Hertz (' Wied. Ann.' 31, p. 983), ' Einfluss des ultravioletten Lichtes auf die 

 Funkenentladung. ' 



1888. 



W. Hallwachs (' Wied. Ann.' 33, p. 308), ' Einfluss des Lichtes auf elektrostatisch 

 geladene Korper.' 



M. Hoor (' Akad. Wiss. Wien. Ber.' 97, p. 719), ' Einfluss des Lichtes auf negativ 

 geladene Konduktoren.' 



W. Hallwachs (Phil. Mag. (5) 26, p. 78), ' On the electrification of metal plates by 

 irradiation with electrical light.' 



1889. 



M. Hoor (' Exner Rep.' 25, p. 91), ' Einfluss des Lichtes auf negativ geladene 

 Konduktoren.' 



A. Stoletow (' C. R.' 108, p. 1241), ' Sur les phenomenes actino-electriques.' 



P. Lenard and M. Wolf (' Wied. Ann.' 37, p. 443), ' Zerstauben der Korper dnrch 

 das ultraviolette Licht.' 



W. Hallwachs (' Wied. Ann.' 37, p. 667), ' Ueber den Zusammenhang des Electrici- 

 tatsverlustes durch Beleuchtung mit der Lichtabsorption.' 



J. Elster and H. Geitel (' Wied. Ann.' 38, p. 503), ' Ueber die Entladung negativ 

 electrischer Korper durch das Sonnen- und Tageslicht.' 



1891. 

 J. Elster and H. Geitel (' Wied. Ann.' 44, p. 722), ' Ueber die durch Sonnenlicht 

 bewirkte electrische Zerstreuung von mineralischen Oberflachen.' 



1893. 

 E. Branly (' Journ. de Physique,' (3) 2, p. 300), ' Deperdition de l'electrioite a la 

 lumi&:'e du jour.' 



1899. 

 O. Knoblauch (' Zeit. f. Phys. Chcm.' 29, p. 527), ' Ueber die Zerstreuung elektro- 

 statischer Ladungen durch Belichtung.' 



1900. 

 H. Buisson (' C. R.' 130, p. 1298) [Abstract in ' Photographic Journal,' June 30], 

 ' Sur une modification des surfaces nietalliques sous rirffiuence de la lumiere.' 



