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 occurred to confirm the truth of his remarks. Dr. Milner properly observes, that there are only three primary 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 have always failed in every experiment to fix the precise limits 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.
