56 



Dr. K. S. Clay. On the Application of 



In the above table the column headed " Average aperture for 

 yellow ink " gives, for each spectrum colour, the aperture of the sector 

 which made the light reflected from the white patch equally bright 

 with that reflected from the patch printed with the yellow ink. The 

 next column, headed " White," gives the aperture of the sector which 

 made the two patches equal when both were white. This column 

 would have been constant but for the polarisation by reflection at the 

 surface of the refracting prism already referred to. From these two 

 columns the proportion of the light reflected by the ink as compared 

 with that reflected by white paper can be calculated. The result 

 appears in the column headed " Per cent." 



In the same way the percentage light reflected by the pink and the 

 red patches were found, and are entered in the fifth and seventh 

 columns. In the sixth column I have calculated the light which should 

 be reflected from a paper printed with both the yellow and the pink 

 inks. The agreement is very fair. The actual red reflects more in all 

 the darker parts than calculated. This may be due to the yellow not 

 being quite so heavily printed, but it is more probably because the 

 pink ink, which was uppermost, was not quite transparent, and some 

 light was reflected directly from it instead of from the white paper 

 beneath. Such light would not suffer by the absorption of the 

 yellow ink. 



The " red " resulting from these printings has a very orange hue, as 

 was to be expected. 



A yellow ink by Mander, No. 226 (Curve No. 25), was less heavily 

 printed than those previously examimed, and therefore seems better in 

 the green and blue green, but the absorption in the violet suffers in 

 consequence. 



A pink ink by Mander, No. 0227 (Curve No. 26), comes up fairly in 

 the violet, but is not opaque enough in the green. 



