Togni, A. “Helmholtz, Du Bois-Reymond, and the Transcendent Difficulty of Explaining the Relation Between Sensations and the Physical World”. Studia Philosophica Estonica, vol. 10, no. 1, Dec. 2017, pp. 83-98, https://ojs.utlib.ee/index.php/spe/article/view/14485.