THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JUL Y 1888. 



I. On the Indices of Refraction of the Metals. 

 By A. Kundt*. 



THE simplest, and at the same time the most reliable, 

 method of determining indices of refraction, i. e. the 

 relative velocities of light in transparent bodies, is that of 

 prismatic deviation. This method has proved available even 

 for strongly absorbent intensely-coloured substances which 

 show considerable irregularity of dispersion in particular 

 parts of the spectrum, if prisms of suitable form are employed. 

 No attempt has, however, yet been made to determine the 

 prismatic deviation of light in metals, since the metals, even 

 in very thin films, are completely opaque. Attempts have, 

 therefore, been made in other ways to draw conclusions as to 

 the velocity of light in the metals. In particular the index 

 of refraction for silver has been calculated by Quincke 

 from various interference phenomena, and by Wernicke 

 from the absorption of light. The indices found by Quincke 

 by various methods are partly smaller than unity, partly very 

 large ; Wernicke finds for silver values between 3 and 5. 

 On the other hand, Voigt calculates from Wernicke's obser- 

 vations the refractive index of silver at about 0'25f. 



Further, from observations on the reflexion of metals BeerJ 

 has deduced the velocity of light in metals according to 

 Cauchy's theory, and Voigtf according to his own theory. On 

 both theories the law of refraction of Snellius is certainly not 



* Translated from the Sitzunyxberichle der kon. Preuss. Akad. der 

 Wmemchaften, Feb. 16, 1888. 



t Compare Voigt on the observations of Quincke and Wernicke, Wied. 

 Ann. vol. xxiii. pp. 104-147, and vol. xxv. pp. 95-114. 



X Pogg. Ann. vol. xcii. pp. 402-419. 

 Phil. Mag. S. 5. Vol. 26. No. 158. July 1888. B 



