Soliloquy is the smoke exhaled by the inmost fires of the soul.

[Le monologue est la fumée des feux intérieurs de l’esprit.]

Victor Hugo (1802–1885) French writer, journalist, human rights activist, politician

The Man Who Laughs [L’Homme qui rit; The Laughing Man; By Order of the King], Part 1, Book 2, ch. 4 (1.2.4) (1869) [tr. Unknown (1869)]
    (Source)

The same wording was used in the Authorized translation (1871).

(Source (French)). Other translations:

Monologue is the smoke of the internal fires of the soul.
[tr. Hapgood (1888); Phillips (1894)]

The monologue is the smoke of the inner fires of the mind.
[tr. Lavelle (2003)]