Philip D. Henderson

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

Henderson, Major Philip D., British Chief of Police who was a member of the party ("Mr. X") at the picnic at Simla at which HPB produced the cup and saucer phenomenon. He joined the Theosophical Society that day and his membership certificate was produced phenomenally on the spot. The next day he became suspicious and resigned. He may have been the person referred to by KH in ML 3-C, p. 11. SH, pp. 146, 148.

Col. Olcott wrote about the Major's change of mind as follows:

Two of the gentlemen—the Major and the one who last joined us—strolled away together, and, after a half-hour, returned in a very serious mood. They said that, at the time when the cup and saucer were exhumed, they thought the circumstances perfectly convincing, and were prepared to uphold that view against all comers. They had now, however, revisited the spot, and made, up their minds that by tunnelling in, from the brow of the hillock, the articles might have been put where they were found. This being so, they regretted that they could not accept the phenomenon as perfectly satisfactory, and offered H. P. B. the ultimatum of doing another phenomenon under conditions to be dictated by themselves. I leave anyone who was acquainted with H.P.B., her family pride and volcanic temperament, to picture to himself the explosion of wrath that followed this speech. She seemed about to take leave of her senses, and poured out upon the two unfortunate sceptics the thunder of her wrath. And so, our pleasant party ended in an angry tempest.

Major Henderson thereafter joined H.P.B.’s critics.