lilms of Sodium and Potassium, 



10 ( > 



exceedingly minute crystals separated by considerable dis- 

 tances, a faint light of a distinctly reddish colour is scattered, 

 when sun or arc light is concentrated on the outer surface of 

 the bulb. This deposit is too attenuated to affect the colour 

 of the regularly reflected or transmitted light to any marked 

 degree. If the deposition is continued, we obtain a film, 

 which is pale blue by transmission, and which reflects light 

 of a straw (pale yellow) colour, both for external and 

 internal incidence. The curves for this film are shown in 

 series 1, fig. 3. Light of a deep violet colour is scattered in 

 this case, though the total amount is very small. If the 

 thickness is still further increased, the external reflexion 

 becomes whiter, and the yellow colour of the internal 

 reflexion more marked. (Series 2 and 3.) 



The kinks in the absorption curves are of no significance, 

 in my opinion, resulting from errors resulting from the use of 

 ray filters for obtaining monochromatic light. 



Further increments in thickness give us films of different 

 shades of purple. (Series 4, 5, and 6.) These films with 



Fig. 4. 



80 

 70 



60 

 50 



40 

 30 

 20 

 10 







































































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46 48 50 52 54 56 58 60 62 64 66 68 70 72 



internal incidence scatter green light. The reflexion for ex- 

 ternal incidence is white. Curves for the golden and purple 

 films made with the Hilger spectroscope are reproduced in 

 4, and may be considered as representing with some 



fig- 



