Newton is thus immersed in a new scientific thought. One day a man came to his house and saw a prism (triangular glass) and asked how much it could cost. At this point Newton considered the scientific importance of the prism and said that it was beyond his power to determine its exact value. As a result, the man demanded a higher price. Newton bought the prism at that price. From this prism he later invented the theory of color.
from:fahim ajmal web page
