Harris admitted he had only seen the plates with his spiritual eyes (meaning he did not see any physical plates):
“While praying I passed into a state of entrancement, and in that state I saw the angel and the plates.” – EMD 2:346-47
“I never saw the gold plates, only in a visionary or entranced state.” – EMD 2:346-47
“He only saw the plates with a spiritual eye” – Joseph Smith Begins His Work, Vol. 1, 1958 “As shown in the vision” – Zenas H. Gurley, Jr., Interview with David Whitmer on January 14, 1885
“Never saw the plates with his natural eyes but only in vision or imagination” – Letter from Stephen Burnett to "Br. Johnson," April 15, 1838, in Joseph Smith Letter Book, p. 2
“They were shown to me by a supernatural power” – History of the Church Vol. 3, Ch. 21, p. 307-308
“...when I came to hear Martin Harris state in public that he never saw the plates with his natural eyes only in vision or imagination, neither Oliver nor David & also that the eight witnesses never saw them & hesitated to sign that instrument for that reason, but were persuaded to do it, the last pedestal gave way, in my view our foundation was sapped & the entire superstructure fell in heap of ruins, I therefore three week since in the Stone Chapel...renounced the Book of Mormon...after we were done speaking M Harris arose & said he was sorry for any man who rejected the Book of Mormon for he knew it was true, he said he had hefted the plates 56 repeatedly in a box with only a tablecloth or a handkerchief over them, but he never saw them only as he saw a city throught [sic] a mountain. And said that he never should have told that the testimony of the eight was false, if it had not been picked out of—–—[him/me?] but should have let it passed as it was..." – Letter from Stephen Burnett to "Br. Johnson," April 15, 1838, in Joseph Smith Letter Book, p. 2
The foreman in the Palmyra printing office that produced the first Book of Mormon said that Harris “used to practice a good deal of his characteristic jargon and ‘seeing with the spiritual eye,’ and the like.” – Mormonism: Its Origin, Rise, and Progress, p.71 Two other Palmyra residents said that Harris told them that he had seen the plates with “the eye of faith” or “spiritual eyes” – EMD 2:270 and 3:22
John H. Gilbert, the typesetter for most of the Book of Mormon, said that he had asked Harris, “Martin, did you see those plates with your naked eyes?” According to Gilbert, Harris “looked down for an instant, raised his eyes up, and said, ‘No, I saw them with a spiritual eye.” – EMD 2:548