Absorption of Light by the Goldberg Wedge. 



77!) 



The values in Table B are plotted in fig. 5. The circles 

 represent points determined with the metal filament lamp, 

 the crosses and solid circles those determined with the 

 mercury are, but with ratios of intensities incident on the 



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wedge of 8*1 : 1 and 23 : 1 respectively. It will be seen that 

 the density is very nearly constant throughout the visible 

 region of the spectrum, though there is a slight decrease 

 from the yellow-green towards the red. In the ultra-violet, 

 however, the density increases rapidly with decreasing wave- 

 lengths. It was thought that this might be due to the 

 presence of gelatine in the wedge, but no absorption by the 

 gelatine alone could be noticed above the accepted wave- 

 length 220 fifi. The values for the gradation in the visible 

 spectrum were verified by means of a Koenig-Martin 

 Spectrophotometer. 



It is evident from the results that while this particular 

 type of wedge is approximately neutral throughout the 

 visible spectrum, there is a very pronounced variation of 

 the extinction coefficient with the wave-length in the ultra- 

 violet part of the region which is normally used in photo- 

 graphic research. 



E 2 



