A further experiment is to look through the prism at a black strip on a white surface. The light colours or the dark will appear at the top or bottom respectively according to the way in which the prism is held. If a pin is placed to mark the extremity of the colours and then the arrangement viewed with the or ordinary eye, it will be seen that the colours were projected on to a white space and a black space. This shows the refraction. The black is, so to speak, projected over the white, giving reds and yellows, and in the other instance white over black, giving the blues. The colours always appear near the edges of black and white.