§55 XX. XXI. COLOURED WRITING PAPER. 161 



has been tested. He has also extended them to different 

 coloured inks, each of two tones, dark and light, on papers 

 of separate tints. The object was chiefly to ascertain the 

 colours of inks a*id the tints of papers least fatiguing to 

 the eye. For this purpose, firstly, twenty-nine or thirty 

 volumes, each containing paper of a different colour, were 

 printed in black ink; and, secondly, twenty or twenty-one 

 volumes, each composed of one hundred and fifty sheets of 

 paper of different colours, or tones of colour, were printed in 

 an ink of a particular hue, which showed the effect of black, 

 blue, and other inks on those several papers. Of the twenty- 

 one volumes, two were in black ink ; two in dark, and two in 

 light, blue ; two in purple ; two in dark, and two in light, red ; 

 two in yellow; two in dark, and two in light, green; two in 

 olive; and one in metallic ink. The subjects printed were, 

 in all of them, tables of logarithms. Though it is not always 

 easy to limit the transition from one tone to another, the 

 sheets of paper may be said to be 



Purple ....... 14 



Blue 13 



Green 23 



Red-pinks, &c 18 



Yellows, orange, buff, &c 42 



Greys and neutral tints . . . .40 



150 



From an examination of these, it appears that while 

 black ink on white paper, being the greatest contrast, has 

 the strongest effect, there are other coloured papers which 

 fatigue the eye less than white ; and this is still more per- 

 ceptible by candlelight than in the daytime. First, as to 

 distinctness : — 



M 



