396 Prof. Stokes on the Metallic Reflexion 



not seem to have noticed in the case of chrysammate of potasb, 

 and which perhaps was not very evident in that salt. In a later 

 paper M. Haidinger had announced the complementary relation 

 of the reflected and transmitted tints*. There is nothing new in 

 employing the rings of calcareous spar as a means of detecting 

 elliptic polarization; and the property of producing elliptic 

 polarization in reflecting plane-polarized light had previously 

 been observed in substances even of vegetable origin f. I am 

 not aware, however, that the chromatic variations of the change 

 of phase had been experimentally connected with the chromatic 

 variations of an intense absorbing action on the part of the 

 medium. I have hitherto mentioned but one instance of this 

 connexion, but I shall presently have occasion to allude to 

 another. 



I think it but justice to myself to point out the error in Cosmos 

 (from whence M. Haidinger derived his information respecting 

 my observations), in consequence of which I would appear to 

 have been guilty of a grievous oversight in the examination of 

 Herapathite : but I would hardly have ventured to mention my 

 observations on carthamine, &c., were it not that, when different 

 persons arrive independently at a similar conclusion, it frequently 

 happens that views present themselves to the mind of one which 

 may not have occurred to another. In the present case, in sta- 

 ting in detail my own views as to the nature of the phenomenon, 



* In a paper of M. Haidinger' s, entitled " Uber den Zusammenhang der 

 Kbrperfarben, oder des farbig durchgelassenen, und der Oberflachenfarben, 

 oder des zuriickgeworfenen Lichtes gewisser Korper," from the January 

 Number of the Proceedings of the Mathematical and Physical Class of the 

 Academy of Sciences at Vienna for the year 1852, will be found a list of 

 M. Haidinger's previous papers on this subject. This paper contains a 

 methodized account of the properties, with reference to surface and sub- 

 stance colour, of the substances up to that time examined by the author, 

 amounting in number to thirty. For a copy of this, as well as several 

 others of his papers, I am indebted to the kindness of the author. 



t More than twenty years ago Sir David Brewster, in his well-known paper 

 * On the Phenomena and Laws of Elliptic Polarization, as exhibited in the 

 action of Metals upon Light," pointed out the modification produced on 

 the rings of calcareous spar as a character of polarized light after reflexion 

 from a metal. (Pnil. Trans, for 1830, p. 291.) In a communication to the 

 British Association at the meeting at Southampton in 1846, Mr. Dale 

 mentions indigo among a set of substances in which he had detected ellip- 

 tic polarization by means of the rings of calcareous spar. In this case, 

 however, he connects the property, not with the intense absorbing power 

 of the substance, but with its high refractive index. 



I do not here mention the minute degrees of ellipticity which have been 

 detected in polarized light reflected from transparent substances in general 

 by the delicate researches of M. Jamin, partly because they are so small as 

 to be widely separated from the ellipticity in the case of carthamine, &c. ; 

 partly because they seem to have no relation to the present subject. 



