The Half Pass originated as a technique to bring cards from the top of the deck around to the bottom, reversed. It appeared in this form in Henri Decremps’s Le Testament de Jérôme Sharp, 1785, p. 161 of the Hugard translation (unpublished), in the context of a Card at Any Number effect. Johann Hofzinser briefly disclosed the modern-day variant of reversing the bottom cards in situ within a letter to friend, Carl von Pospischil on Oct. 27, 1847. This letter can be found in Magic Christian's Non Plus Ultra Vol. 1, 1998, p. 265 of the Pieper translation, with a full description of the technique following in Non Plus Ultra Vol. 2, 2004, p. 36 of the Pieper translation. Six years after Hofzinser's letter, the method hit the printed page in Jean-Nicholas Ponsin's Nouvelle Magie Blanche Devoilee, 1853, p. 49, with no credit to Hofzinser, or anyone else.
This approach doesn't seem to appear in the published record again until the late 1920s and early 1930s: A Half Pass in which only the bottom portion is turned over in a routine by Jack McMillen is described in the posthumously published Page Wright's Manuscript, 1991 (written ca. 1929), p. 171. See also Bob Fisher's trick, “Something With Double Backed Cards,” in The Sphinx, Vol. 32 No. 12, Feb. 1934, p. 372, in which Mr. Fisher defines which of the two Half Passes (top-to-bottom or in situ) he is referring to.
Also see Half Pass Covered by a Stripout Action.