This article draws upon a range of nineteenth- and early twentieth-century accounts of magic performance to argue that the success of an illusion was dependent upon the spectator's engagement with the trick as a conscious application of mechanical effects. The stated aims of the magicians' art, as evidenced by their published statements, but also by the nature of their applied techniques, was that audience response was not to be a simple form of stupefaction, but a lively interaction with the performance as both a meticulously composed spectacular sight and as a contribution to a broader fascination with technology and illusionism. Spectators were encouraged, directly or indirectly, to make comparative assessments of the illusions with which they were presented, based on their knowledge of earlier instances of the same tricks or on their awareness of published exposs of popular effects. This kind of collusive illusionism is carried into the filmic realm, as demonstrated significantly by the work of the French film-maker Georges Mlis. In adapting his popular stage illusions for incorporation into the new film medium, Mlis prompted comparisons between the different versions of the same tricks, thus highlighting the distinct and defining characteristics of each medium.