FRAGMENT XII. 



CONCERNING COLOURS 



ADDRESSED TO WILLIAM WILBERFORCE, ESQ, M. P 



SIR, 



Many years have elapsed since you first called 

 my attention to that Theory of Colours, which your learned 

 friend, Dr. Milner, permitted me to publish in his own words 

 in 1803. During this interval frequent opportunities have oc- 

 curred to confirm the truth of his remarks. 



Dr. Milner properly observes, that there are only three pri- 





mary colours, red, blue, and yellow; although Sir Isaac Newton 

 also mentions orange, green, indigo, and violet: but these are 

 compounds of the other three; and whether in the rainbow, or 

 the prism, they appear to melt gradually into each other; and I 

 ave always failed in every experiment to fix the precise limit > 

 of each tint; but in the course of some late investigations, I have 

 accidentally discovered certain appearances, from which I have 

 derived some facility in colouring Landscape. 



Having placed a piece of dark cloth on a wall opposite to the 

 light, I fastened a sheet of white paper in the middle of it; this 

 I looked at through a prism held across my eyes a little above 



H 







