"[W]ith a Perpendicular right Line drawn cross from one Side to the other, distinguished it into two equal Parts. One of these Parts I painted with a red Colour and the other with a blew. The Paper was very black, and the Colours intense and thickly laid on... This Paper I viewed through a Prism of solid Glass... Beyond the Prism was the Wall of the Chamber under the Window covered over with black Cloth, and the Cloth was involved in Darkness... These things being thus ordered, I found... the Light which comes from the blew half of the Paper through the Prism to the Eye, does... suffer a greater Refraction than the Light which comes from the red half, and by consequence is more refrangible."