Adjustment of colour in various pupse, etc. 431 



■ Z.— APPENDIX. 



THE QUALITY OF LIGHT FROM THE COL- 

 OURED AND OTHER LAOKGROUNDS 

 EMPLOYED IN THE EXPERIMENTS RE- 

 CORDED IN THE PRESENT MEM(JIR. (Sir 

 John Conroy and E. B. P.) 



My kind friend Sir John Conroy, F.R.S., ac^ain helperl 

 me to make a correct analysis of the light reflected from 

 the backgrounds employed in our experiments. The 

 papers, etc., were examined in the Laboratory of Balliol 

 College, Oxford, on July 24th, 1899. The beam from an 

 electric arc was passed through a bisulphide of carbon 

 prism, and the spectrum thrown on a white paper screen 

 in a darkened room. The coloured papers, etc., were held 

 so as partly to cover the spectrum, and sometimes two 

 were held in the spectrum .'^ide by side for purposes of 

 comparison. The method was thus the same as that 

 made use of on the previous occasion (Trans. Eut Soc. 

 1892, /. c. pp. 459 et seqq.), except that the lime-light 

 illumination was then employed, and our spectrum was 

 therefore weaker at the blue end than with the electric 

 arc. The results obtained are recorded below. 



I. Coloured backgrounds, etc., employed by F. Mcrrijield: — 



Black net and black tissue-paper (used as a plane surface 

 and also rolled round sticks). The reflected light from 

 both gave a feeble continuous spectrum. The trans- 

 mitted light was the same but still feebler. 



Dark sticks also gave a faint continuous spectrum : 

 cork carpet was similar except that the reflected red was 

 prominent. 



Orange tissue-paper (used as a plane surface and also 

 rolled round sticks). Some absorption of green and more 

 of blue and violet ; absorption more marked in the sticks 

 where ttiere was more than one thickness of the paper. 

 No appreciable difference between the reflected and trans- 

 mitted spectrum of the paper. The spectrum was far 

 more like that of a yellow paper than of the deep 

 orange used in my experiments, which removed everythino- 

 except the red, orange, and yellow. 



Orange leno gave a very similar spectrum, the blue and 

 violet being almost cut otf, and the green a little darkened. 



