Louis Bertrand Castel

Louis Bertrand Castel (5 November 1688[1][2] – 11 January 1757[3][4]) was a French mathematician born in Montpellier, who entered the order of the Jesuits in 1703.

[6] He wrote several scientific works, that which attracted most attention at the time being his Optique des couleurs (1740), or treatise on the melody of colours.

[4] Early on, Castel illustrated his optical theories with a proposal for a Clavecin pour les yeux (Ocular Harpsichord, 1725).

Pressing a key caused a small shaft to open, in turn allowing light to shine through a piece of stained glass.

[9][10] Castel thought of colour-music as akin to the lost language of paradise, where all men spoke alike, and he claimed that thanks to his instrument's capacity to paint sounds, even a deaf listener could enjoy music.

A caricature of Louis-Bertrand Castel's "ocular organ" by Charles Germain de Saint Aubin
Castel's 1740 comparison of Newton's spectral colour description with his explanation in terms of the interaction of light and dark, which Goethe later developed into his Theory of Colours .
Mathématique universelle abregée à l'usage et à la portée de tout le monde , 1728