Seurat took to heart the color theorists’ notion of a scientific approach to painting. Seurat believed that a painter could use color to create harmony and emotion in art in the same way that a musician uses counterpoint and variation to create harmony in music. Seurat theorized that the scientific application of color was like any other natural law, and he was driven to prove this conjecture. He thought that the knowledge of perception and optical laws could be used to create a new language of art based on its own set of heuristics and he set out to show this language using lines, color intensity and color schema. Seurat called this language Chromoluminarism.
His letter to Maurice Beaubourg in 1890 captures his feelings about the scientific approach to emotion and harmony. He says “Art is Harmony. Harmony is the analogy of the contrary and of similar elements of tone, of color and of line, considered according to their dominance and under the influence of light, in gay, calm or sad combinations”.
Seurat’s theories can be summarized as follows: The emotion of gaiety can be achieved by the domination of luminous hues, by the predominance of warm colors, and by the use of lines directed upward. Calm is achieved through an equivalence/balance of the use of the light and the dark, by the balance of warm and cold colors, and by lines that are horizontal. Sadness is achieved by using dark and cold colors and by lines pointing downward.
 A Sunday Afternoon on the Island of La Grande Jatte
A Sunday Afternoon on the Island of La Grande Jatte shows members of each of the social classes participating in various park activities. The tiny juxtaposed dots of multi-colored paint allow the viewer’s eye to blend colors optically, rather than having the colors blended on the canvas or pre-blended as a material pigment. It took Seurat two years to complete this 10-foot-wide (3.0 m) painting, much of which he spent in the park sketching in preparation for the work (there are about 60 studies). It is now in the permanent collection of the Art Institute of Chicago.
Seurat made several studies for the large painting including a smaller version Study for A Sunday Afternoon on the Island of La Grande Jatte,, 1884-1885, that is in the collection of the Metropolitan Museum of Art, in New York City.