Jelasin soal Johann Karl Friedrich Zöllner dong

Johann Karl Friedrich Zöllner () adalah seorang astrofisikawan Jerman yang mengkaji ilusi optik. Ia juga merupakan seorang investigator psikikal.

Transcendental Physics (English edition, translated by Charles Massey, 1880)

Eleanor Mildred Sidgwick. (1886–87) Results of a Personal Investigation into the 'Physical Phenomena' of Spiritualism. With Some Critical Remarks on the Evidence for the Genuineness of Such Phenomena. Proceedings of the Society for Psychical Research 4: 45-74.

Ulrici, Hermann. (1879). Der sogenannte Spititismus eine wissenschaftliche Frage. Zeitschrift für Philosophie und philosophische Kritik 74: 239-271.

Wundt, Wilhelm. (1879). Spiritualism as a Scientific Question: An Open Letter to Professor Hermann Ulrici, of Halle. Popular Science 15: 577-593.