The last method of recomposing white light was one more suited to vulgar apprehension. It consisted in attempting to compound a white by mixing the coloured powders used by painters. He was aware that such colours, from their very nature, could not compose a pure white; but even this imperfection in the experiment he removed by an ingenious device. He accordingly mixed one part of _red lead_, four parts of _blue bice_, and a proper proportion of _orpiment_ and _verdigris_. This mixture was _dun_, like wood newly cut, or like the human skin. He now took one-third of the mixture and rubbed it thickly on the floor of his room, where the sun shone upon it through the opened casement, and beside it, in the shadow, he laid a piece of white paper of the same size. “Then going from them to the distance of twelve or eighteen feet, so that he could not discern the unevenness of the surface of the powder nor the little shadows let fall from the gritty particles thereof; the powder appeared intensely white, so as to transcend even the paper itself in whiteness.” By adjusting the relative illumination of the powders and the paper, he was able to make them both appear of the very same degree of whiteness. “For,” says he, “when I was trying this, a friend coming to visit me, I stopped him at the door, and before I told him what the colours were, or what I was doing, I asked him which of the two whites were the best, and wherein they differed! And after he had at that distance viewed them well, he answered, that they were both good whites, and that he could not say which was best, nor wherein their colours differed.” Hence Newton inferred that perfect whiteness may be compounded of different colours. As all the various shades of colour which appear in the material world can be imitated by intercepting certain rays in the spectrum, and uniting all the rest, and as bodies always appear of the same colour as the light in which they are placed, he concluded, that the colours of natural bodies are not qualities inherent in the bodies themselves, but arise from the disposition of the particles of each body to stop or absorb certain rays, and thus to reflect more copiously the rays which are not thus absorbed.