168 



M. G. Quincke on the Optical Properties 



account the values of a for transmitted light differ slightly from 



those for reflected light. 









Table IV. 









a = 



=45°. a = 7 r -128. 



« = 45°. a = 7 r -603. 





Transmitted light. 





Reflected light. 



I. 



P« 



8. 



/V 



& 



P- 



S. 



0. 



o 



r 





O / 



O / 



r 





o / 















45 35 



45 35 













20 



0-522 



0-0732 46 49 



45 27 



0-374 



00492 



44 41 



30 



0-904 



0-1269 51 20 



46 15 



0-760 01 000 



43 46 



40 



11 78 



0-1653 56 27 



45 59 



1-094 [01439 



42 49 



50 



1-484 



0-2082 63 10 



49 25 



1-774 ' 2333 



39 51 



60 



2-086 



0-2927 69 59 



50 50 



2-892 ! 0-3804 



35 20 



70 



2-3S6 



0-3321 77 45 



51 40 



4-842 0-6368 



32 5 



75 



2-766 



0-3880 80 24 



54 50 



6444 0-8476 



28 17 



80 



3-728 



05230 83 2 



55 10 



8-782 1155 



27 29 



Observations made upon other transparent plates of platinum 

 furnished similar results. Here again, just as for silver, the 

 difference of phase and the azimuth (3 (under the same incidence) 

 were found to be the greater the less transparent the films. 



But it is impossible to form a just idea of the thickness of 

 the films from their degree of transparency ; for the same metal 

 presents various degrees of transparency, as has been shown by 

 Faraday. In the optical properties of the metals, and in the 

 influence which they exercise upon reflected or transmitted 

 light, there was observed the widest differences — and, indeed, not 

 alone as regards silver, which one might suppose to undergo 

 oxidation, but also with regard to gold and platinum, of which 

 this supposition is inadmissible. 



The optical constants of the metals may be calculated, accord- 

 ing to Cauchy's theory, from the principal angle of incidence 

 A, for which the difference of velocity of the components, polar- 

 ized parallel and perpendicular to the plane of incidence, becomes 



—. and from the azimuth H which belongs to it, and which 



4 ° ' 



represents the restored polarization when the incident light was 

 polarized in the azimuth a = 45°. 



Cauchy has given only the data and the results of his calcu- 

 lation. A more detailed development is to be found in the 

 papers of Beer* and Eisenlohrf, the; latter of whom gives for- 

 mulae which enable us to calculate with accuracy the refraction 

 and extinction-coefficients at perpendicular incidence. 



• Pogg. Arm. vol. xcii. p. 402. 



t Ibid. vol. civ. p. 374. 



