During the nineteenth century, scientist-writers such as Eugène Chevreul, Nicholas Ogden Rood, and David Sutter wrote treatises on color, optical effects, and perception. They were able to translate the scientific research of Helmholtz and Newton into a written form that was understandable by non-scientists. Chevreul was perhaps the most important influence on artists at the time; his great contribution was producing the color wheel of primary and intermediary hues.