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Capping the deck is used on the gaming tables, so it might have been a cheating technique before coming to use in conjuring. It was published with cards hiding underneath a book, and then dropping that book on a tabled packet to secretly add the cards in Ellis Stanyon's Magic, Vol. 13 No. 2, Nov. 1912, p. 12. Walter B. Gibson later introduced a more natural built-in context by using a prediction in an envelope (with the force card hidden beneath the envelope) in his “A Spirit Card Trick” from Two Dozen Effective Practical Card Tricks, 1927, p. 30.