Henry Slade

According to Readers Guide to The Mahatma Letters to A. P. Sinnett:

Slade, Dr. Henry, an American medium of exceptional talents. He was thoroughly tested by HPB and HSO and was picked by HSO and others to go to Russia for scientific tests of his phenomena. At one time he gave special courses to professors of Leipzig University in Gemany, and as a result Prof. Zollner published a book Transcendental Physics in which he challenged the world to account for Slade's phenomena save by a "spiritual" hypothesis. The book was translated into English by C. C. Massey ... See bibliography HPB I: 525; ML index; ODL I: 201; SH, pp. 13, 18, 74, 166.

Additional resources

• "Huxley and Slade." The Banner of Light (October 28, 1876). Available at Blavatsky.net and reprinted in A Modern Panarion by H. P. Blavatsky.
• Milner, Richard. "Charles Darwin and Associates, Ghostbusters." Scientific American (October 1996). Available at Scientific American. Reposted with commentaries at Spiritualismlink.com.
• Milner, Richard. "Charles Darwin: Ghostbuster, Muse and Magistrate." Survival of the Fittest: Celebrating the 150th Anniversary of the Darwin-Wallace Theory of Evolution Issue 9 (2008). Journal of the Linnaean Society in London. Available at Darwinlive.com.
• Wikipedia has useful links, as well.