Physics. — "Experimental hiquirj/ into the Xature of the Surface- 

 Layers in the Reflection by Mercury, and into the Difference 

 in the Optical Behaviour of Liquid and Solid Mercury". 

 By Dr. J. J. Haak and Prof. R. Sissingh. (Communicated by 

 Prof. H. A, LoRENTz). 



(Communicated in the meeting of September 29, 1918). 



1. Introduction. Since in 1850 L. fiORENZ ^) advanced the suppo- 

 sition, tliat the elliptical polarisation on reflection by transparent 

 bodies is the consequence of a gradual transition between the two 

 adjoining media and elaborated this view theoretically, the influence 

 of these surface layers has been more than once theoretically inves- 

 tigated, both in case of the reflection by transparent bodies and by 

 metals'). There have, however, been made only few experimental 

 investigations into the nature of these surface-layers and our know- 

 ledge of it is confined to more or less plausible suppositions. Great 

 influence is always assigned to the grinding and polishing and also 

 to the grinding and polishing material itself, with which these ope- 

 rations are made. An investigation by Rayleigh shows, however, that 

 it is not yet possible to state in what way this influence arises '). 



Besides, an influence of the condensed gas layers has often been 

 supposed and examined *). Up to now however, attempts to demon- 

 strate the influence of a condensed gas layer have not yet succeeded. 



2. Purpose of the research. In order to obtain the optical con- 

 stants of a metal, quite independent of the grinding and polishing 

 and the material used for this purpose, mercury was chosen for this 

 investigation. Both the liquid mercury and a mirror of solid mercury 

 can be examined. It becomes then also evident, whether at the transition 

 from liquid to solid mercury the optical constants are subjected to a 

 modification. In the investigation of liquid mercury the impression, 



1) L. LoRENZ, Pogg. Ann., Ill, 460, 1860; 114, 238, 1861. 



2) C. A. VAN Run van Alkemade, Thesis for the doctorate, Leiden, 1882; Wied. 

 Ann., 20, 22, 1883. P. Drude, Wied. Ann.. 43, 126, 1891; R. G. Mac Laurin, 

 Proc. Roy. Soc, (A), 76, 49, 1905. 



») Rayleigh, Proc. Roy. hist, 16, 568, 1901. 



•i) J. J. Seebeck, Pogg. Ann., 20, 35, 1830; P. Glan, Wied. Ann.. 11, 464, 1880; 

 R. Sissingh, Thesis for the doctorate, Leiden, 1885; Arch. Néerl., 20, 171,1886. 



