THE 



MERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. IX. — An Experimental Investigation on the Reflec- 

 tion of Light at Certain Metal-Liquid Surfaces / by Lynde 

 P. Wheelek, Assistant Professor of Physics, Sheffield Scien- 

 tific School of Yale University. 



Introduction. 



When light is incident on a transparent substance at an angle 

 whose tangent has the numerical value of the index of refrac- 

 tion of the material, theory, as embodied in the Presnel equa- 

 tions, demands that the reflected light should be plane polar- 

 ized in the plane of incidence. Experience teaches, however, 

 that but for a very few substances, solid or liquid, is this 

 true. Most substances show at this angle an elliptic polariza- 

 tion of small ellipticity. This ellipticity (denned as the ratio 

 of the amplitudes of the components of the vibration parallel 

 and perpendicular to the plane of incidence) is found to be 

 sometimes positive and sometimes negative. (Positive elliptic- 

 ity corresponds to a counter-clockwise description of the ellipse 

 when viewed from the side of the incident light.) 



That this well-nigh universal though small discrepancy 

 between theory and experiment cannot be entirely assigned to 

 contamination of the reflecting surface seems to have been 

 definitely settled by the experiments of Lord Rayleigh on 

 very clean water surfaces.* He found that as the surface was 

 made progressively cleaner, the negative ellipticity previously 

 observed became numerically smaller, passed through a zero 

 value, and for the cleanest surfaces obtainable, assumed a very 

 small positive value. On the other hand, Drude, working with 

 the fresh cleavage surfaces of transparent crystals where the 

 chance of surface contamination is very remote, found that 

 within the limits of error of observation the ellipticity van- 

 * Phil. Mag. (5), xxxiii, p. 1, 1892. 



Am. Jour. Sci.— Fourth Series, Vol. XXXII, No. 188.— August, 1911. 



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