No man lives in the external truth among salts and acids, but in the warm, phantasmagoric chamber of his brain, with the painted windows and the storied wall.

Robert Louis Stevenson (1850-1894) Scottish essayist, novelist, poet

Essay (1888-02), “The Lantern-Bearers,” sec. 3 Scribner’s Magazine, Vol. 3, No. 2
    (Source)

Collected in Across the Plains, ch. 7 (1892).