330 Prime Angle of Incidence o/Fraunhofer's Lines. 



to one another, the prime angle of incidence and prime azimuth 

 change very considerably in the same direction, only more than 

 with a layer of pure silver particles on glass. Moreover, with 

 a suitable pressure and reflection in air the prime azimuth may 

 be nearly the same for blue as for red. 



Whether the silver-collodion film be unpolished or polished, 

 the particles of silver have always a different distance from one 

 another, or a different distribution, in the vicinity of the glass- 

 surface and in the vicinity of the free surface bounded by air; 

 so that the reflections in air and in glass are not directly com- 

 " le. 



According to the distribution of the silver particles in the 

 interior of the collodion, which varies of course with the nature 

 of the exposure in its preparation, the prime angle of incidence 

 and prime azimuth vary for different colours, and the silver col- 

 lodion-film (photographic plate) exhibits various colours under 

 the incidence of natural white light, which may be different for 

 reflection in air and in glass. 



Precisely similar is the behaviour of substances with so-called 

 surface-colours, with which H and B increase and diminish with 

 increasing wave-length. 



Carthamin, dried in a red- coloured transparent layer on the 

 faces of the above-mentioned parallelepipeds, exhibited, with 

 reflection in the same substance, different reflection-constants in 

 different parts, according as the distance between the particles 

 was less or greater. The parallel-mirror method showed, for 

 light of the given wave-lengths X (in millionth parts of a milli- 

 metre), the following mean values of the prime angle of inci- 

 dence H and prime azimuth B : — 





Reflection in Air. 





A. 



H. 



B. 



656 



... 59 2 



4 52 



589 



... 64 30 



8 56 



555 



... 63 18 



14 24 



527 



... 60 27 



Reflection in Glass. 



21 58 



656 



... 55 12 



8 56 



589 



... 59 2 



7 24 



555 



... 57 39 



14 25 



527 



... 63 48 



10 32 



486 



... 61 46 



15 32 



460 



... 61 48 



24 2 



431 



... 61 14 



26 41 



