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The pocket card—used to add a double Louis d'or secretly to a bet after it had proven successful—appeared in an anonymous book, Les misters du phraraon dévoilés…, 1810. Daniel Rhod mentions this in Notes on the History of Cardsharping in France, 2011, p. 23. John Kennedy later reinvented this coin-holdout idea in his marketed “Impossible Matrix”, 1978.
J. N. Hofzinser used a pocket card for a different purpose: to receive a borrowed finger ring, after which the open end of the card was sealed with diachylon, and later the ring was produced from inside the card. See “The Insoluble Impromptu” in J. N. Hofzinser: Non Plus Ultra, Vol. II, by Magic Christian, 2013, p. 290.
Ellis Stanyon described a pocket card to secretly hold more cards in Magic, Vol. 14 No. 2, Nov. 1913, p. 17.