How did Jean Le Rond d’Alembert contribute to the theory of music?

Jean Le Rond d’Alembert made several significant contributions to the theory of music through his writings and scientific research:

• Exposition of Harmonic Theory: In his 1752 work, Éléments de musique, d’Alembert sought to explain and popularize the harmonic system developed by the composer Jean-Philippe Rameau, which became the dominant framework for Western music until the 20th century.1
• Acoustics and Physics of Sound: D’Alembert applied his mathematical expertise to the study of sound. He published treatises on acoustics and the physics of sound within his mathematical opuscules. Notably, his development of partial differential equations in the 1740s allowed him to derive the general wave equation, which he famously applied to the problem of vibrating strings in his 1747 work, Recherches sur les cordes vibrantes.123
• Encyclopedic Contributions: He authored several articles on music for the Encyclopédie and published Réflexions sur la musique en général et sur la musique française en particulier (1754), which detailed his thoughts on music, specifically regarding the French tradition.1