I have some questions for magic historians in the group. In 1939, Columbia Pictures released a serial entitled "Mandrake the Magician." Warren Hull played Madrake. Hull performs several largely self-working illusions throughout the chapterplay including a dice box trick and a much simplified (and occasionally editor aided) miser's dream. In the first episode, Hull puts on a "program" including several effects that, like the miser's dream, were clearly chosen by someone with some knowledge of magic.
During this show, someone performs a very good cups and balls routine (though, some amazingly dim light at Columbia cut the final revelation from the routine---the last thing we see are two hands setting up a final load). All we see throughout the cups and balls routine are the performer's hands. These hands are supposed to be Hull's. However, it is quite clear that they belong to a practicing professional and that Hull is simply doing voice-over patter.
I'm assuming it's fairly likely that the person who performed the cups and balls is the same person who provided Hull with instruction in performing the other routines/tricks.
I'd like to know if anyone in the magic community has any idea who might have been technical advisor on this film and who might have performed and taught Hull these tricks. Being a serial, the film never identifies any technical support. So, unless someone can help with information, the magician's credit may be as lost as most nitrate film stock.