
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.

Bathers at Asnières,
1884, National Gallery, London

The Circus,
1891, Musée d'Orsay, Paris