The Most Beautiful Possible Line

Paul Valéry considered Victor Hugo’s alexandrine “L’ombre est noire toujours, même tombant des cygnes” the most beautiful possible line in all poetry. This article investigates the linguistic perceptions underwriting Valéry’s evaluation, suggesting how synesthetic perceptions of vowels might inform his versificatory ideal. I begin by showing how poetic aspects of language shape perceptions of vowel brightness and coloring in late-­nineteenth-­century psychology studies of audition colorée (Galton, Gruber, Flournoy), then proceed to bring out the surprising resemblance between the behavior of vocalic color in these scientific reports and in roughly contemporaneous poetic discourse (Hugo, Mallarmé, Banville). Attending particularly to Stéphane Mallarmé’s sonnet “Le vierge, le vivace et le bel aujourd’hui . . .” (1885) and Hugo’s own reflections on vowels’ colors and brightnesses (1836–­68?), I bring out the coherence of the nineteenth century’s scientific and poetic discourses, long obscured by the twentieth century’s establishment of consistency as synesthesia’s defining feature.